Link 3-Colour 90

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INTRODUCTION

 

Interest in colour is part of the nature of man. Pliny (Como 23 A.D.- Stabia 79 A.D.) thought that atoms were coloured. Leonardo Da Vinci (Vinci 1452 - Amboise 1519) wondered why the sky is blue. Lord Rayleigh (Langford Grove 1842 - Witham 1919) was struck by the colours of the flowers. Chevreul (Angers 1786 - Paris 1889) loved the harmony and composition of colours. Shakespeare (Stratford on Avon 1564 - 1616) used coloured images in his powerful poetry. Boyle (Lismore Castle 1627 - London 1691) had the intuition that colour was a sensation provoked by light. Padre Grimaldi (Bologna 1618 - 1663) was convinced that colour depended on radiation. Young (Milverton 1773 - London 1829) gave great importance to the colours red, yellow and blue. Newton (Woolsthorpe 1642 - London 1727) wanted to understand how to generate the colours. Goethe (Frankfurt 1749 - Weimar 1832) was fascinated by shades of colour and by grey. Dalton (Eaglesfield 1766 - Manchester 1844) was quite surprised when he noted that his perception of some colours was different to the perception of his friends. Helmholtz (Potsdam 1821 - Charlottenberg 1894) saw the colours as a function of wavelength. Armstrong (in 1969) was immediately attracted by coloured reflections of some lunar rocks ...

 

Colour and art

For artists the effect of colours, rather than their chemical and physical structures, is essential. Even though the chromatic effects can be controlled and measured, either by visual perception or by physical apparatus, the fact remains that there is a secret chromatic which lies in the soul alone and which eludes every concept. Although painters are often dedicated to the study of chromatic laws, the teaching and the theories serve in periods of decadence while in periods of greatness, which is the case for any art or science, intuition prevails in an irrational untutored rapture. A comparison with music is quite revealing: a musician who knows composition well but is without inspiration will always be boring. Similarly a painter without inspiration will always have a limited expressive power.

Leonardo, Dürer (Nurinberg 1471-1528), Grünwald (Wurzburg 1740- Halle 1528), el Greco (Crete 1541- Toledo 1614), and other great painters were not ashamed to investigate conceptually the artistic possibilities of the formal elements with the scope of demonstrating fundamental laws and principles in the world of colours. Knowledge of the laws of composition is useful for making the painter more confident in himself or at least it should be so. On the other hand the so-called laws of colour are only partially valid given that the effect of colour is complex and irrational.

Colour is life.

The colours are creatures of light and light is the mother of the colours. Light, the first phenomenon of the Universe reveals, in the colours, the vital spirit and the soul of our world.

The summer passing of a falling star, the phantasmagoria of a fireworks display, the rainbow, provoke our admiration and, in some cases, our sentiments. Our spirit is quieted in contemplation. Colour, gives forms an intense and spiritual vibration. J. Itten (Berne 1888 - Zurich 1967) says "... the primordial essence of colour is an oneiric harmony, is music become light. In the moment that one starts to think about colour, to formulate laws and concepts, to place principles, their perfumes vanish and nothing but bare material remains in our hands ...".

Therefore, we do not know the meaning of colour, its laws and its analysis in a scientific way. Colour, beauty, sentiments belong to the eyes and the heart and to the intimacy and subjectivity of human beings. They are not accessible to measurement nor to any association, or collectivity, be it of scientists or laymen. It is very important, however, to think of colour not only in physical terms, that is, it is not only received from a single object but from light and from the colours of the environment, from the shades which the surrounding objects produce, from the lights and the interactions which exist. The sentiment of the Chemist, the Biologist or the Biochemist in contact with colours or rather with coloured molecules is completely different.

 

History of colours in art

Colour has always played an important role in ancient civilizations and is a tangible testimony of the art and the psycology of those peoples. Initially the colours used were red and yellow ochres, and white and black.

Lively colours and intense polychromatics frequently appear among the Egyptians and Greeks. In China painting developed from the Han period (80 B.C.). Intense colours are seen in mural paintings and on wood in the Tang period (618-907 A.D.) along with blue, red,and green ceramic glazes. Almost contemporaneously painting on silk and on paper developed. In this period black ink was much used with all its touches. In the Sung period (960-1280 A.D.) sensibility to colour became refined in an extraordinay way, especially in ceramics, with the introduction of very beautiful colours like the tender green or the "claire de lune" blue.

Passing to the same period in Europe, (1000 B.C.), strong polychromics are found in Roman and Bizantine mosaics.

The high-medieval Icelandic miniatures of the 8th and 9th centuries posess lively and varied chromatics. Great luminosity and hot and cold tones, as are found much later in the impressionists and in Van Gogh, appear in several pages .

For artists of the Romanic and Gothic periods colours had a symbolic value and therefore pure expressive colours without shade differentiations or tonalities were used.

Giotto and the Sienese school were the first to characterise the figure in forms and in colours, thereby starting the process which would, after 1400, bring about that extraordinary multiplication of personal styles which distinguishes European art in the 15th, 16th and 17th centuries.

In the first half of the 15th century the brothers Hubert (1370-1426) and Jan (1390-1441) van Eyck, initiators of modern painting, would examine the real world with extreme technical perfection and precious touches of colour. And it was thus that colours became a means for characterising natural things.

Piero della Francesca (Borgo S. Sepolcro 1410-1492) painted figures with clear borders making use of pure and intensely balanced colours, balanced by their complements; the tints are not very varied but have a very original timbre.

Leonardo da Vinci avoided every chromatic vivacity and composed paintings with extraordinarily subtle tonal modulations, like the sepia chiaroscuro of S. Girolamo and the Adoration of the Magi.

In his first works Titian (Pieve di Cadore 1490- Venice 1576) isolated and opposed large areas of uniform colours, then decomposed these areas into hot and cold, light and dark, opaque and bright pictoric touches while in his old age his paintings are dominated by single colours rich in chiaroscuri.

With his disciple, el Greco, the coloured areas no longer have any descriptive value but are organised in relation to the pure agreements of form and colour. A strong counterposition of colour to colour is found in Grünewald.

In Rembrandt (Leiden 1606 - Amsterdam 1669) chiaroscuro painting reaches its highest point. In this great painter, especially in the Amsterdam period, blacks, reds, golds and whites prevail while the painting expresses more and more internal emotion.

From the Empire to Neoclassicism occasionally brightened by some colours we pass to the romantic palette. This had its origins in England with Turner (London 1775 - 1851)) and Constable (East Bergholt 1775 - London 1837) and in Germany with Friedrich (Grifswald 1774 - Dresden 1840) and Runge Wolgast 1777 - Hamburg 1810). Turner, (author among other things of a Gulf of Baia, near Naples) and the other romantics, used colour as a psycho-expressive means for giving spirituality to the countryside and at times extend to the dissolution of the object to such an extent that they appear to be the precursors of abstractism.

Now we arrive at the beginning of the 19th century where interest in physics, in chemistry, in the theory of colours and the meaning of colours is greatly increased. In this context the chromatic revolution of the impressionist painters came about, with the careful observation of natural phenomenology, solar light and the study of the atmospheric effects on the landscape, arriving at painting a single subject in different ecological conditions. New pictoric forms were achieved.

The neo-impressionists went further and dissolved the chromatic marks into points of colour, sustaining, influenced by the theory of colours of Chevreul, one could only have an ideal mixing of the colours in the eye of the observer.

With the picture of van Gogh (Zundert 1853 - Auavers sur Oise 1890) entitled "Caffè nocturne" one wishes to close the chapter, given the essentially conservative spirit, without adding or subtracting anything. One refuses, that is to discourse on the contemporary painting. The representations, the criticism, the interpretations are of J. Itten. But the criticism, the sensation, the internal emotions are also those of the reader and escape any personal examination or any scientific law.

The painting reproduced here shows a street café, illuminated in a street immersed in the darkness of the night, the terrace engulfed by the hot light is yellow-orange, without any other descriptive tonalities; and its clear tint contrasts with the dark houses and with the blue-viola nocturnal sky spattered by stars. All the tonalities of yellow are represented here.

The orange marks on the black-blue facades of the houses represent the illuminated windows. In the depth of the dark street some figures dissolve. At the end of the terrace of the café there are some last customers. The small illuminated windows give and impression of solitude and squalor.

Here one finds the relation of the night sky with the smallness of man. The artificial light contrasts the external light of the stars.

The dominating yellow creates, together with the orange of the terrace, a simultaneous contrast with the blue-viola which highlights both the yellow and the orange.

Also the yellow-green of the walls and the dark green of the tree, contrasting with the red marks and lines scattered here and there, produce simultaneous contrasts. The chromatic force of the painting is also increased by the asymmetric composition.

 

Physics

A ray of light which crosses a triangular prism decomposes into various colours. In the rainbow small drops of water provoke the same effect as the prism. The colours are seen because the light is decomposed into radiations of different wavelengths. The radiations or rays at low wavelength (475 mm) produce the sensation of a violet colour, those of a high wavelength (645 mm) that of the colour red, while the intermediate wavelengths produce blue, green, yellow and orange.

Almost all objects do not emit their own light, they are "seen" because the re-emit a part of the light which stikes them. In common language, always a little coarse and little scientific, one says that the light is transmitted or reflected, without taking into account, (it could not be different given the socio-cultural preparation of the mass-media or as one once said, of the borgeois), of the atomic and molecular mechanism which comes into play as soon as a light source irradiates a body.

White light, for example that which comes from the sun, is a mixture of electromagnetic radiations of wavelengths between 400 and 700 mm and with a distribution of intensity characteristic of the radiation emitted by a body at 6000°C. When such light strikes an object the following events may occur:

a) the light is re-emitted without variations of frequency;

b) light is absorbed and its energy is transformed into thermic energy;

c) the light is re-emitted under the form of visible light of a lower frequency: That is, the phenomenon of flourescence occurs;

d) the light reflects on very thin layers or films giving rise to the phenomenon of interference.

Now let us imagine a single atom of molecule exposed to light. Quantum theory, currently, tells us that light propogates in the form of packets of discrete quantities called photons. The higher the frequency of the light the more energy contained in the photon.

Quantum theory also tells us that the energy of an atom or a molecule can take certain well-defined values, characteristic of every atomic or molecular type, which are in general indicated as characteristic spectrum of the atom or the molecule. Usually an atom is found in the fundamental state, that of minimum energy, but when it is exposed to light of a frequency such that the energy of the photon equals one of the differences of energy between one excited state and the fundamental state the atom absorbs a photon and passes to the corresponding excited state. We "see" the colour. In a small time the atom falls into a lower energy state and emits the difference of energy under the form of a photon. This simple scheme must be known by the painter and must be taught in schools.

Two colourations can be defined simply and are easy enough to understand for the mass media: black and white. A body which reflects all the rays of white light, that is, without,absorbing any is perfectly white. A body which absorbs all the rays of white light without reflecting any is black.

The interaction of light with material includes reflections (interference is a type of reflection which happens on very thin films or layers), refraction, diffusion, absorption, re-emission of the radiation with different wavelength or fluorescence.All the effects of these interactions depend or may depend on the wavelength of the radiations and also in this case we have colours. The painter must have, as seems more and more clear, a knowledge and understanding of these phenomena and their scientific meaning. We reassume, mainly for the painter or for the artist, the various relations which are known between colours and the physical state.

Electronic excitation (laser, discharges in gas, lightning, flames, sparks) vibrations (green and blue colours of water) composites of transition metals (pigments, torquoise, rubies, emeralds, amethyts) charge transfer (magnetite, saphire blue) conjugated links (animal and vegetable) metalic conductors (copper, iron, gold) pure semiconductors (cinnabar, diamond, silicon) doped semiconductors (blue diamonds, yellow diamonds, luminous diodes, amorphous natural semiconductors (melanins, ), refraction with dispersion (rainbow), diffusion (blue of the sky, red of sunset, Tyndall effect), interference (film of petrol on water, colours of some insects), diffraction grills (opals, liquid crystals, some colours of insects and fish). Definitively speaking colour, starting from the case of vibrations of the atoms in a molecule, starts from the change in of state of electrons (excitation of electrons) of matter.

Schemochromes and pigments

The colours and shades of animals are due to the phenomenon of selective absorbtion of light by chemical compounds called pigments or to physical phenomena or to both phenomena. The pigments are also called biochromes and the colours of physical origin are called schemochromes. It is easy to distinguish a biochrome from a schemochrome: the former can be extracted by a solvent the latter cannot. All animal pigments can be isolated and often obtained in the form of crystals. There are not blue,green crystallisable pigments in the animal kingdom.Naturally at equal concentrations there is no difference between the colour of the pigments seen in the animals and those isolated in the laboratory. The fact of being able to study the pigments independent of the biological sources is a great advantage for who proposes to establish the formula of the structue of a molecule. The formulae of the structure are one of the most pursued discoveries of Science. Besides indicating to us how the various atoms are linked together among themselves and distributed in space they give us precious information on the biogenesis, the function, the evolution of the organisms, genetics, and on how to construct models of molecules useful to man.

 

Schemochromes or pigments which do not exist

The glass prism or droplets of water produce the colours because of a physical phenomenon. Several colourations of animals are due to the phenomena of dispersion, of interference and of the diffraction of light. The optical objects responsible for the physical phenomenon, which nature builds with incredible perfection, can be made of particles, microscopic prisms, grates, stripes, thin layers and cavities; a complete engineering applied to colour.

One of the most beautiful colours of a physical origin which is met in the animal world is blue. One has this manifestation with particles, honeycomb cells and other optical constructions when the diameter of the particles (0.6 mm) is of the same order of size as the wavelength of blue light and when there is a difference between the refractive index of a particle and that of the material which surrounds it. The presence of a dark screen makes the blue visible.

This type of blue is seen only by reflection, while with transmitted light reddish, brown and grey colours appear. The size of the particles determines the intensity and the tones of the blue; the blue of the sky increases in industrial zones where smokes composed of very fine particles are present, while if there are larger particles present they make the blue faded. After a storm the sky is bluer because the rain makes a selection of the particles taking down the larger ones.

The beautiful blue eyes of a blonde girl, the blue of the plumage of birds, of some reptiles, fish and invertibrates are all due to this physical phenomenon, that is, to schemochromes.

It is easy to demonstrate by a simple experiment that the blue colour of the animals, which we call Tyndall effect, is not due to a pigment. Blue eyes are too precious to be wasted and so for this we shall use the blue feather of a bird; finely ground in a moarter until its cellular architecture which produces the blue is destroyed, the colour disappears while the resulting powder has a greyish colouration.

The numerous green colours in animals are of a singular origin. The green has its origins in a blue schemochrome provided with a yellow pigment which acts as a filter. The green eyes in man which we consider of rare beauty and those of other mammals are due to the combined action of a blue schemochrome with a yellow pigment. The yellow pigment is almost always soluble in some solvent and can be therefore extracted. The experiment by which one can change a green of an animal into blue can appear almost magical. Vice versa the addition of a yellow pigment to the blue produces a green. This is a new cosmetic for ladies with blue eyes. In 1979 , on the invitation of our friend the superintendent Raffaello Causa, we worked in the chemical laboratory of restoration work of the Musem of Capodimonte. In that period, of which one has a happy memory, we had the chance to observe that in several canvasses, coming from the 1600s, the green had been obtained overlaying a transpaent yellow film on a blue pigment; the painter, that is, had used a schemochrome. With the passing of the years the thin yellow film had been destroyed and that which was green had become blue. The restoration which follows strong laws all turned to conservation alone found itself in front of an difficult question: restore the green of the hill or leave a blue hill.

White originates in a different way. The surfaces and the colloidal phases are constituted by materials which do not absorb light and which have a state of subdivision such as to not interfere with the wavelengths of visible light. They reflect white light without altering it and for this reason they appear white. Tissues made of interwoven keratin interspersed by spaces of air are responsible for the fur of the polar bear and other mammals. However the animal schemochrome remains for the "uninstructed man" a mysterious fact.

Schemochromes also continue to produce their beautiful colours after the death of the animal. It is enough to think of the scarabs found in Egyptian tombs still conserve their splendid colours. The fact that these marvelous colours of a physical origin, unlike the pigments, have not yet found a practical use is a great surprise. Timid attempts are found in some cloth or tissue obtained by weaving thread of different colours, and adorning clothes with pieces of glass or by the inclusion of sand can obtain walls and sheets with different coloured effects according to whether they are seen with reflected light or transmitted light, as happens for the colours produced by the animal schemochromes.

Where positive results seem to have been obtained seems to be in the field of mosaics and in coloured glass. In the mortuary chapel dedicated to San Lorenzo at Ravenna, vulgarly called the Mausoleum of Galla Placidia, there is a suggestive bright light provoked by the fact that the blue mosaic of the walls is illuminated by orange light which penetrates into the chamber, like a fine paintbrush, through the thin alabaster windows. Observing from different points, reflections alternate, now blue now orange, and as with some animals, one has the sensation of a coloured spray isolated in the atmosphere.

A simple but surprising effect is that produced by coloured windows. In this case the colourant is contained in the glass and when the light strikes the coloured glass it is partially reflected by the surface as happens for normal glass. This effect though is not usually very pronounced, since the most conspicuous reflection is produced by oscilators with resonances in ultraviolet as in common glass. The fraction of light which penetrates inside the glass, the refracted wave, is subjected to the absorbing effect of the colourant and as a consequence only the light of the non-absorbed frequency can cross the glass, it is for this reason that one obtains certain marvelous chromatic effects when white light crosses coloured glass. The colour of the glass appears less intense when one observes the illuminated side. In fact, the reflection on the surface is practically without colour and the main visible colour is produced by the light which, penetrating inside the glass, is then reflected by the second surface.

The stained glass windows of the cathedral of Chatres at the time of sunset enter in "resonance" with the sun producing a chromatism of great effect and which produces in the observer a beatitude, similar to the celestial tones of Thaïs from the violin of Fabrizio von Arx.

To reproduce the complex architectures which produce the physical colours of the animals certainly constitutes a problem, perhaps also of an economic nature. If this could be resolved the palette of the painter would pulse in new multicoloured world, their paintings would be given of a new strong and decisive expressive force like that which was given by the different ecological situations of the impressionists. This, in the future. Certainly it is not the corrupt and disturbed fantasy to which the student movement inspired, in the 1970s, in the fine (horrible) arts. To all this we should like to add the scientific and biochemical inspiration which the chemist A.M.Liquori has indicated many times in the artistic field.

Cities also have their colours: Naples is blue, Lecce is yellow, Bologna red-brown, Turin black. Many of their colours have disappeared, externally eaten away by a cloud of pollutants but they survive in interiors. The longer the old remains the longer the colour is conserved. A city which is conserved and exhibits a strong colour is San Francisco determined to survive despite the adversities of nature. Certainly everything contributes; the coloured and bright magic during the daytime in the Gulf of Naples produces a mystical sense in the soul, at the same time a physical exaltation of beauty. The houses of San Francisco brighten with the passing of the hours and the changes of weather in shades of vermillion red, blue green, yellow of straw and yellow of ochre. This city subjects you to its painted houses; and is perhaps, externally, the most coloured city in the world. Many people believe that the relation with colour here is an exorcistic relation with the unknown future of the Earth which shakes.

Pigments

If for a moment we think about the colours of a bird, to those of the butterfly or of tropical fish and compare them with the mammals we are really disappointed. In mammals there are not very pure colours which go from yellowish to reddish, to red-brown, grey and black, with a monotony which is only broken by the alternation of shades as occurs in spotted, dappled or speckled animals. In a parallel with the arts we can recall the sober and realistic black, white and grey painting of the Empire and of Neoclacissism.

The pigments called melanin and pheomelanin contribute to the various colourations of the mammals. They generate starting from several precursors like DOPA (Torquati 1913), cysteinyldopa (Nicolaus 1964), tryptophan (Hopkins 1901). A combined action of these precursors can contributes to the variety and shades of the "colours".

These three compounds, after having suffered a series of chemical transformations which, in the mammals, lead to a series of black, brown, red-brown pigments with a large variety of tones The pigments deriving from tryptophan seem to be isolated in the skin and the fur of marsupials and therefore constitute a characteristic of aplacental mammals.

Dopa and cysteinildopa undergo several transformations before forming pigments. An attempt to connect the various transformations together is shown in the scheme on the next page. One is dealing with a true soup, worthy of appearing in the pre-enzymatic age.

And what can be said of melanogenesis? Writing in 1962 on the biogenesis and the structure of the melanins;

 

"From all these data it would seem to be reasonable to conclude that Raper's Scheme, which requires melanin to be polymers of 5,6-indolequinone, grossly simplifies the problems of melanogenesis; such a scheme should be understood, assuming that a number of different intermediates may take part in the formation of the macromolecue (particles). The extent to which the different intermediates take part in the construction of the pigment varies with variations in the biological or chemical conditions leading to products which may be different even though they start from the same substrate.The scheme is perhaps still too simplified since, when free radicals are formed, phenolic intermediates could contribute to the formation of the macromolecule, and in the end, its irregularity is increased by the formation of pyrrole units from the breakage of indole units. The final results is a complex particle built from heterogeneous and easily tautomerizing units, which are linked together by bonds (more than one type) that are not easily broken by hydrolysis. This situation makes it difficult to establish the sequence of the units and to obtain good yields of breakdown products of the "macromolecule". Sepiomelanin is a highly disordered natural "macromolecule" which cannot be broken by hydrolysis; it is the first example of its kind from an animal source. The method of enquiry into this surprising structure requires an altogether new approach in organic chemistry".

 See now Link14,20.21,22.

Melanins: biological and chemical chaos

Many intellects have been immolated to the moloch or melanin. Some researchers change in time turning to more fruitful fields of research. I remember A. Angeli, A. Quilico, L. Panizzi, M. Piattelli, E. Fattorusso, L. Minale, D. Sica, C. Santacroce, S. Magno, S. de Stefano, G. Sodano, G. Cimino, G. Scherillo, E. Novellino, G. Allegri, H. Wyler, J. Bu'Lock, J. Harley-Mason, G.A. Swan, M.S. Blois, H.G. Khorana, S. Bouchilloux, R. Robertson, R.J.S. Beer. An example of attachment to melanin is seen in G. Prota.

 

 

 

Melanogenesis and Phaeomelanogenesis

 

* isolated

Phaeophenol = stage of 5,5-Dihydroxyndole

Phaeoquinone = stage of 5,6-Indolequinone

 

The most important success consigned is the understanding that the chemical physical and biological study starts from erroneous theoretical presuppositions, uses erroneous investigation methods, reaches erroneous conclusions and is always controversial. In 1968 it was still repeated that it was the incapacity of the instruments available to bring a contribution to our knowledge of the structure of melanin. This does not mean to say that the study of pigmentary cells is useless but rather that this could be of great importance for man.

The first work which was done in the past was the demolition study of the pigment, that is the use of one of the classical methods for establishing or contributing to establishing the structure of the substance and which had had so much success in the study of natural substances. Effectively if one excepts oxalic acid, which is abundant in oxidative demolition, no fragment is worth interest. Study turned towards identifying the intermediaries of melanogenesis does not produce the desired effects for structuristic ends either, and is at most limited to identifying some precursor beyond which there is a dense darkness.

Eumelanins: derived from dopa and tyrosine. These compounds copolymerise with several other chemical molecules for which the classification or the assignment to this class is a difficult problem. In fact the discovery for example of nitrogen or sulphur in an allomelanin (Link 5) could make one think of a eumelanin or a pheomelanin while instead one is dealing only with a substance in which both nitrogen and sulphur molecules have been copolymerised or result from the high binding property of melanin.

Pheomelanins: derived from various cysteinyldopas. Also these can copolymerise for which reason the assignment to this class is even more difficult; for example to define substances containing only nitrogen and sulphur in the proportions required by the theory. In this field we meet the pigments called trichromes (pheochrome) for which a well defined structure is known. They can also crystalize but there is no proof that they are natural pigments, that is that they contribute to the colours of animals.

Allomelanins: form from non-nitrogenated or non-sulphurated precursors common in the vegetable kingdom, for example: pyrocatechol, 1,5-dioxynaphthalene. Sometimes for these pigments the classification on an analytic basis is difficult if not impossible in that in the course of their formation, that is in that complex radical cocktail, nitrogenated, sulphurated and heterogeneous substances are incorporated in the pigment.

All these substances cannot be described according to the rules of molecules structure. This is strange and should at least make the modern scientist curious. What are the mysteries which lie behind these substances?

Many works use the old investigation schemes and apparatus which, are normally used for studying the chemical structure and the biogenesis of crystalline and ordered compounds. We must conclude, unfortunately, that it has not been possible to make any progress, compared to our first research, regarding the chemistry and the biochemistry of these substances.

Despite this a false chemistry, a false biology and a false physiology have developed, and the investigations carried out to date have been equally false and meaningless for the structures of the natural pigments. Even the simplest data like the evolution of CO2 during melanogenesis, the change in pH, the production of H2O2 or the recognition of the sequence of free radicals which are generated starting from tyrosine remain without interpretations.

The crystalline substances are common in nature: everything, even vulcanic lava, tends to a crystalline state and molecular order. Only a few substances are amorphous in the natural state: melanins, pheomelanins, lignins, carbons. These are all very common substances in nature. They do not have a molecular weight, they are like a man without a soul, and this assumption would be enough to impede every structure investigation and to impede biological investigation as well. Without the crystal the powerful tool of the investigation which had so many successes in the field of natural substances did not work. Some information comes from X-rays which tell us that in the pigments there are many superimposed layers as happens in graphite and that the colour should be due to the dispersion of light more than to highly conjugated systems of electrons. More recently colour was attributed to the gap of band model semiconductors.

Current science has at its disposition powerful chemical and physical weapons for investigating the structure of crystalline compounds and their biological functions while it is completely disarmed in front of the amorphous state. Neither is this study followed and encouraged; for example the Nobel prize has been assigned only to researchers of ordered crystalline substances with a molecular weight.

If for a moment we leave the mammals and descend along the philogenetic scale we find very beautiful colours both for their variety and their tonality. It is interesting at least for the biologist and the taxonomist, to note that to all these colours and colourations correspond a number of pigments, that is to a limited number of chemical structures, as can be seen in the following table:

 

 

YELLOW (carotinoids, pterins, flavins, uranidines, zooxantines)

ORANGE (carotinoids, pterins, ommocromes)

RED (carotinoids, pterins, ommocromes, porphirins, naftoquinones, anthraquinone)

GREEN (schemochromes, bile pigments, carotenoproteins, clorocruorins, pheophorbides)

BLUE (schemochromes, bile pigments, carotenoproteins)

VIOLET (carotenoproteins, ommocromes, naphtoquinones)

RED-BROWN (pheomelanine, melanin, copolymers)

BROWN (pheomelanine, melanin, copolymers)

BLACK (melanin)

GREY (melanin, mixture of black and white)

WHITE (schemochromes, refraxtion and reflection of light)

 

The intensity of the colour of the skin depends mainly on the colour and the form of the granules of pigment, on their number and on the way in which they are distributed in the keratinocytes. For example the difference in colour between negroes and mongols is due to the fact that the granules in the first are isolated and spread in the second they are found in localised groups in some vescicles of the keratinocytes.

The synthesis of the melanin pigment is made by an enzyme called tyrosinase by many, but which would be better named poliphenoloxydase poikilopolymerases.

The absence or the inactivity of the enzyme is the cause of that disease in man and in other animals known as albinism. This metabolic error, which is congenital, discolours the skin and the hair and makes the eyes sensible to light and generally shortens life. It is distressing to think that the light which produces life and makes all the beauty of nature stand out joyfully can for some beings constitute a hostile element and a source of pain. Albinism is also known in other mammals besides man but it is rather rare in those which live in the wild because they are eliminated by natural selection.

A hyperactivity of the enzyme can, vice versa, produce large areas of highly pigmetnted skin and be associated with those tumours called melanomas which are seen on the skin of a large number of animals from fish to man.

The pigment of the skin, like all the black bodies, reflects only a small part of the incident light which is, therefore, mainly transformed into heat. Strongly pigmented skins "are hotter", maintaining the absorbed heat for longer and have a more difficult hydric exchange than white skins. The quantity of melanin can influence the production of vitamin D which causes ricketts when it is missing, Vitamin D is formed in man by the action of ultraviolet rays of solar light on some sterols. Electrical and sound conductivity are more pronounced in black skin.

These biological differences between white skins and black skins can be the base of serious and dramatic social problems.

 

Changes of colour

For man the change of colour can often be a dramatic fact. Modifications in the colour of the skin indicate serious illnesses. The sudden darkening of a mole can be the sign or the presence of cancer. Whitening of hair, a phenomenon in which the activity of tyrosinase decreases slowly until it ceases altogether, is the sign of decline. In alcaptonuria, a metabolic illness of a genetic nature, the sweat, the nails and the skin can appear coloured. Some parts of the skin take on a more or less blue shade after the ingestion of some pharmaceuticals. Less worrying and rather rare is the phenomenon which makes human sweat appear red, yellow, green and even black because of a dysfunction of the cellular membrane together with an excessive ingestion of certain foods and coloured products. As an aside and for curiosity one can recall that the hippopotamus normally sweats red because of a not yet well studied pigment.

The only change of colour which can be considered a frequent and normal occurrence is that which under the term suntan and is clearly visible in the skin of the white races.

When the radiation hits the skin a part of it reflects, a part is absorbed or dispersed and a part penetrates beyond the horny layer. Here the radiation transforms many molecules into free radicals which, as is known, finding themselves in an anomalous state of valence, are extraordinarily reactive and combine with every other type of molecule inducing processes which no longer obey the cellular laws.

While man is completely unaware, taken by a sudden melaninic raptus lying flat out on the burning sands, the ultraviolet rays penetrate in the most vital parts of the skin upsetting the ordered processes of the metabolic production line.

Contemperaneously the action of the sun sets off, fortunately, the antiradical operation. The enzyme tyrosinase comes out of hibernation, produces a large number of granules of pigment which are transferred to the higher layers. In this stage the free radicals polymerise, or are copolymerized together with substances toxic for the cells. Also the horny layer gets thicker, the urocanic acid absorbs energy and is transformed from the trans form to the cis form. The entirety of these biological operations ends up with providing the skin with a protective shield against the radiating action.

The pigment of the skin, because of its capacity to link or copolymerize a large number of substances in the course of its genesis provides the organism with a means for the elimination of substances which are toxic for the cell; almost like the action which happens in the liquid phase via the kidney. We can say that melanocity is a cellular detoxifier which exercises its action in the solid phase. For this reason this pigment must have been very important in the preenzymatic era when it was important to purify the environment of substances (eg: free radicals) toxic for biological systems which were starting to become organised. Thus the radical soup was transformed into an inert product (melanin) which, was also using as a matrix or molecular lattice.

A more refined and physiological way of increasing the pigmentation would be the use of injections of hormones which are normally indicated by the initials MSH (Melanocyte Stimulating Hormone).

The meaning of changes in colour in other mammals is completely different. The ermine has a darker coat in summer and is white in the winter. This is due to temperature. Ermine bred in hot environments produce dark fur in the winter period. In weasels the colour of the fur depends on the light, that is, on the different length of summer’s and winter's days. It is probable that, for other animals, the colour of the hair is influenced both by the temperature and by the light for example dopachrome produce DHI by heating. The Himalayan domestic rabbit is born with all white fur but then the points of the nose, the ears the tail and the paws become black. One may note that the extremities are found more exposed to the cold winter. The alpine hare presents different mutations in relation to the variations of temperature, in the light and the hormonal influence, the white fur becomes progressively substituted by grey and brown hair: this change of colour allows the animal to adapt to the colour of the environment and constitutes a system of defense against enemies.

Red hair

Most of the reddish and brownish colouration of the hair of mammals are due to pheomelanins (Link 14). Also freckles on human skin owe their colour to this pigment. According to the concentration and the form of the granules of the pigment they can also have tonalities of colour which go towards yellow and pink. The colours are never pure as those imparted by other pigments like for example the carotenoids. One thinks for example of the red of a mature tomato from a carotenoid.

There are various colourations of human hair: carrot-red, orange, Titian-red, red-brown. This variety of tints can be explained with the quantity and the type of pheomelanin and pheochromes present in the hair. Another tonality of colour can derive from a chemical process which involves both melanogenesis and pheomelanogenesis and from a process of copolymerization. Individuals with red hair find themselves in a biologically disadvantaged situation compared to those with black hair because the red pigment does not offer an adequate protection from solar radiation. The irritable character which is aften associated to men with red hair can be today explained in molecular terms thinking of photosensibility which some metabolites of pheomelanin possess. What are the environmental and biological conditions which determined, among our ancestors, the synthesis of a red pigment and what functional role did this pigment play in the past?

Haemoglobin

Haemoglobin which colours the blood of animals red and which has the vital function of carrying oxygen from the lungs plays a modest role as a visual pigment or in exhibition in mammals.

The red colour of the cheeks, especially evident in children of the North, is due to very thin skin which allows the haemoglobin to be seen.

The pink and red colours which can be seen on the tongue and on the point of the nose, in the ears and on the buttocks of many mammals, that is, in all those zones where the fur or the mucous is very thin. The African mandrill and other apes present red areas of the body because of high vascularisation of the cute and their red-blueish parts because of a combination of the red of haemoglobin and black of the melanin of the skin. Other zones especially the buttocks may be blue because of a decidedly schemochromic effect.

One class of pigments which are affine, from a structural and biogenetic point of view, to the chromophore system of the haemoglobin are the porphyrins. These pigments contribute very little to the colours of mammals but we know one interesting case represented by the teeth and bones of the Americal squirrel Sciurus niger which are the reddish brown colour from a porphyrin. The pigment can be shown up irradiating the bone tissue with ultraviolet light, in that the porphyrin is fluorescent.

Because of a metabolic disturbance, in general hereditary, the teeth and bones of man can also be coloured by the porphyrin. It is unfortunately a serious illness which, besides having several symptoms and serious sufferance, makes the patients strongly photosensible because of the porphyrin.

 

The eye of the Galago

The lemurs have grey, brown or rust coloured fur because of the presence of melanin and pheomelanin. These mammals have large yellow-reddish eyes and a very acute vision even at night. Their eyes, struck by a swathe of light, shine in the dark like two headlamps. The yellow pigment of the Galago crassicaudatus constituting the tapetum lucidum behind the retina consists of crystallised riboflavin. Riboflavin is known as vitamin B2 and it is a real surprise to find it accumulated in the eye of the galago.

 


Artificial colourations

The African bat Lavia frons covers its skin with a yellow dust, produced by glands which are found in the lower part of the body as if it were a cosmetic. It is difficult to say though whether such behaviour is intentional as it is in man.

The history of colours as ornament is ancient and full of meaning. Colours and coloured patterns had great importance, especially in times of war, among primitive and ancient races. Julius Caesar was impressed when he met the first Britans with blue and viola skin and thought that they painted themselves to scare the enemy.

The art of colouring oneself, quite common one time still now survives, also if its primitive meanings are being lost, among the Maori, Papuans, Japanese, and some African tribes. Australian aboriginies paint their faces with strips of yellow or red ochre, charcoal, soot, white chalk, for the ritual which signals the end of puberty. Very extensive tattooing is carried out in the Marshall Islands where all the body is covered with black and red colouration. The skin is perforated with needles or with special sharpened apparatus which are applied and hammered while they are hot, all in a deafening noise of drumming and singing which covers the cries of the unfortunate. The Eskimos operate in a different way passing a thread covered with soot under the skin. After being taken out this leaves black lines. The Australians practice scarification: cutting the skin and filling the wound with coloured clay and adding ashes to aid scar forming. The meaning of tattooing is quite different according to the place and the time in which it has been practised: esthetic, erotic, a sign of power, a sign of vengeance, or memory of an oath or as recognition. More rationally, it was practised in the Second World War in the American army to indicate the blood group of soldiers.

With coloured cloth one almost has the impression that man wants to rival the splendid liveries of the birds and insects. The great variety of colourants available today, given the great development in synthetic organic chemistry and the low production costs, allow human fantasy full play.

In the past the colourants used to dye cloth were of natural origins, very expensive , and used with a secret art passed down from father to son. Famous among the colourants of antiquity is the precious porpora (purple) which can be extracted from a mollusc of the Mediterraneaan coasts, and which can dye, according to the procedure used, fiery red, viola or red-black. Used to dye the Greek papyruses, the tissue of the Phonecians, Egyptians, Romans and still in the early Medieval to dye the clothes, from which the Italian name porporati of cardinals and priests. Recalled by Homer, Aristotle and Virgil for its beauty and its high cost, it was the colourant of kings and of dignitaries.

The porpora of the ancients, porpora of Tyre, royal porpora are synonyms for the colourant

 

The beautiful Tyrian purple  see on Federico da Montefeltro

 

 obtained from the working of the glands of molluscs of a type, common in the Mediterranean, Murex. The production represented in antiquity a considerable industry for several Mediterranean, Asiatic and African countries. According to some, originally the centre of production was not in Tyre (ancient Phonecian city today a small village in Libanon called es-Sur) but at Leuke a small island south east of Crete. In the glands of the molluscs there are halogenated and sulphurated precursors (SCH3, SO2CH3) of indole which because of the double hydrolisis and oxidative processes provide the precious pigment. The dying was made directly on the cloth. The cost of this colourant was very high, about 200 denari, at the time of Caesar Augustus, per kilogram; about 6,500,000 lire in 1987.

 

The message of colour and the expressionist theory of colours

Colour provokes many thoughts. Many of these must be linked to a memory which has prehistoric roots, where colour played an important role in the life of man.Colour still serves us today in the choice of food and the environment in which to live.The evolution of life is connected to these gigantic molecules which, organising into complex three dimensional structures, have used smaller molecules, rich in functional groups able to interact with light and to trap energy.The oldest biological structures, grown in the saline womb of the sea, have dilated their surfaces to light and, in a thousand year march which has seen chlorophyll as a protagonist, abandoned the muddy depths and covered the Earth with primordial tones.In the aerobic area new macromolecules formed around the primaty chromatic nucleus adapting it to a new function, the transportation of oxygen. The evolution of life is a startling coloured event recalled by the "memory" impressed in the Blue Algae and in the myth which has given a divine message to the rainbow.Slowly the biological material found new forms of expression and colour spread everywhere becoming a characterising element of living material.Although science is currently able to explain the physical and chemical nature of the phenomenon "colour" completely, the same cannot be said about its biological meaning and, for most of the coloured substances present in nature, the biochemical logic which induces the genesis and the accumulation of specific pigments inside the cells and in the specialised cellular ultrastructures, eludes us. These synthetic processes, presided over by complex and differing enzymatic systems, but ubiquitous in nature, are certainly the expression of precise and necessary biological work in which the appearance of coloured products is, if nothing else, the index of a significant biochemical modification in the cellular field.

The polychrome liberation 1945,August Andrè Bauchant pinxit, Musee d’Art Modern, Paris.

 

 Functional interpretations of the pigments, attempted by naturalists and evolutionists through an anthropocentric vision, has attributed the colours with functions correlated to the life of relations: that is the colours of the flowers function as a call, even if the "individuals" to whom the message is turned are particularly sensitive to different wavelengths, thus also the melanin of the octopus has been assigned the function of defense, while it seems by now verified that such a function is not linked to the black cloud as much as to the presence of a toxic quinone secreted with the black and destined to hit specific receptors in the olefactive cells of the aggressor, and in conclusion, even the melanin of the human skin does not appear as the most indicated substance for protecting new skin from the lesive effects of ultraviolet radiation. Electrical and sound conductivity are peculiar properties. In any case, the polychrome of nature so much loved and observed, although still offering stimulating problems, does not evoke the interest it deserves perhaps because, while it remains fascinating, we have, for years, unconsciuosly found the justification for its exitence in its own beauty.What was and what still is the delusion of Man to discover himelf nude not only of fur but also of colours is amply demonstrated by the lively activity which he has always used for modifying his own colour. Coloured substances, depigmenting substances, dyes for the skin, dyes for the hair. The use of the colours was, perhaps, one of the oldest discoveries born from the need to express and to exorcise fear, to externalise the Io, desiderous of leaving its own print. Man soon learnt to become patron of the colours of plants and animals using them to extend to infinity the colourability of his body and of objects, he has surrounded himself with colours, he has coated everything. Colours have entered his mind, his memory and in psyche, becoming symbols of a code, words of an instinctive and universal language, testimony of an intimate and innate tendency to expressionthrough colour evoking, perhaps, an ancestral link with the processes which marked the origins of life.The history of man is impregnated by colours and they interweave with him in an irriducible array of symbols, of allegory and of messages.Green: fecundity, hope, nature, springRed: blood, passion, power, sensualityYellow: sanctity, knowledge, wisdom; but also according to the tone, falsity, serenity, wealth.Naturally, the "coloured" message is elaborated in a different way according to the specialisation of the person. The expert values its fertility from the colour of the countryside and what to cultivate from the colour of the soil. Some plant diseases are identified by the colour. The colour of the patient helps the doctor in his diagnosis. The chemist takes information on the nature of the substances, from the colour of his test tubes, classifies them and establishes if a reaction has happened, or is going well.There is a vast literature on the reactions of man to colour. The entire organism appears to be influenced by colour. Different types of emotion and levels of activity may be linked to the intensity and the wavelength of light. The colour purple is majestic and therefore ends up by becoming unbearable, yellow is lively, green relaxing, blue partially diminishes activity and makes us lazy. Colours can often replace words with meanings which are just as precise: among the Zulus (South Africa) the beloved is offered a red and white box and, accepts the lover offering a red, white and blue necklace.

 

Dominique Peyronnet (1878-1943) The Ocean

In pre-Colombian Mexico, if a painter inserted a figure dressed in red in his representation, the faithful referred that figure to the god of the Earth Xipe Totec, and therefore to the direction of East, meaning dawn, birth, youth, spring. That is, the figure was not painted red on the basis of optical esthetics or on psychic-expressive values, but its colour had the semantic value of a letter of the alphabet or of a heiroglyphic.

In the historical style called naïve the past and the present do not exist. The naïve painter do not follow traditional scheme but operate as a free man. The art is expression of joy.The nature and the sea are represented with a typical steadiness

 

 

 

Andrè Duranton,  “ Cat ”, 1973

Berry-Lardy Gallery, Paris

 

 

 

 

In the Catholic Church the heirarchy of priests is indicated by symbolic colours which reach up to the porpora of the cardinals and the white of the Pope. To characterise the ecclesiastcal cerimonies the priests have to wear robes of a rigourously prescribed colour. It is clear that every sacred art of a high level uses the colours in a symbolic way. It is interesting to note that like in pre-Colombian Peru, in the Tiahuanaco style, the colours were used in a symbolic sense, in the Paracas style in an expressive sense and in the Chimu style in a sense which we would call impressionist.

 

 

The red and yellow of the  peruvian desert, the blue of the ocean, the grey of the sky in the Paracas painter of Patrizia Badinotti - Nicolaus  (Lima 2000).   Patty_ art@hotmail.com     

Looking at the historical styles we find peoples which used the colours only as symbolic elements, to indicate emblematically the different social classes, levels or castes, or mythological or religious ideas. An even deeper interaction between man and colour is clearly seen when one examines the effect which some colours exercise on the metabolism influencing the psyche and the behaviour of individuals.

Itten recounts: one day I had given to a painting class the theme of a still life with a free choice on the production, from the extremes of realistic representation to abstract geometric nexus. Four days later I saw a student destroy with an orgasm his own realistic still life. On the canvas, after an hour of hard work, there remained only a bloody mess, similar to a disgregated tissue. Later the student suddenly left the school withour giving any further news of himself. I made investigations on the state of the student's health and had this reply from his companions: the doctor has sent him to Davos, in a sanatorium. Eight days later news of his death arrived. In his last picture his febrile and corroded pulmonary tissue was reflected".

Without doubt colours have a deep and upsetting influence which acts irrespectivly, whether the consequences are recognised or are ignored.

Men prefer blondes. This is a commonplace. The triangle man-woman-blonde has at least one lightly erotic side. Recent statistics establish that the children of blondes are healthier than those of brunettes; which makes the preference for blondes increase.

Red light brings about an increase in blood pressure and in respiratory rhythm? One says "seeing red" to indicate a feeling in which one presumes that the presssure is high. The increase in blood pressure can explain the aggressivity of the bull at the sight of the famous red cloth. The discontinuous and nervous throb of the motors waiting at the red traffic-light almost seems the result of the high blood pressure of the car-drivers.

It is very difficult to reach a scientific evaluation of the influence of the colours on man from these natural experiences.

But if we consider our dreams we find that sometimes they are more or less intensely coloured because active molecules are spontaneously liberated in the organism or are volontarily put in the circulation (drugs) and hit receptors of the membrane of the specific neurons. This interaction between the colours and the behaviour states must particularly interest people who work professionally with colours and with their use.

In this category we may include shop-fitters and in general all the places destined for public use, advertising designers who must choose appropriately between the colours which are most suitable to make a product inviting. We may add all the operators in the field of the formation of pharmaceuticals and of food additives who, for a long time, have not excluded the use of toxic colourants so as to better lure the world of infants. Substances which impart lively colours, even if highly toxic, to wrappings of foodstuffs, with still obscure scientific scopes, are liberally used in the so-called developed countries.

To be able to evaluate the single colours in their specific psychological and spiritual expressions one needs to examine them comparitively. We limit ourselves to an example one on the psychological and expressive value of yellow: because we love yellow in all its hues, in all its most intimate meanings.

In China yellow, the most luminous colour, was reserved for the emperor, Son of the Sky. Apart from him nobody could wear a yellow clothes. Yellow is the symbol of the highest wisdom and illumination. During mourning the Chinese wear white to indicate that they are accompanying the deceased into the celestial reign of purity. They do not express, therefore, their personal pain in mourning, but wearing white clothes help the deceased to reach the reign of perfection.

Yellow is the most luminous colour but it immediately loses its brightness when darkened by grey, black or viola. Yellow is like a denser and more substantial white. The more profoundly this light, becomes yellow, penetrates in the depth of the mixture, the more it transforms, passing from orange-yellow to orange and to orange-red. Red signals the limit point for yellow and does not remain contaminated in a noticible way. Orange is at the centre of the progression yellow-red and represents the most powerful and vigorous synthesis of light and material. Golden yellow represents the highest sublimation of material by the work of light, irradiating a diffuse luminosity, without transparance, like a pure vibration. Gold was largely used by primitives. It meant luminousity, irridescence. The gilt mosaics on the bizantine cupolas and the golden backgrounds of the old masters are symbols of the world beyond death, of miracles, of the reign of the Sun and of the Moon. The golden halo of the Saints is a sign of their spiritual light. That celestial light could only be indicated visually by yellow. Yellow is often associated with intelligence, knowledge and transcendence. Thus synagogues are rationally represented by yellow. Just as there is only one truth there is only one yellow. If the truth is camouflaged, obscured or altered the result is something which is the contrary of the truth. Thus camouflaged, obscured or altered yellow evokes falsity, diffidence and dementia.

Judas has often been painted with darkened yellow. The grey yellow generally evokes a sensation of disquiet, while if accompanied by dark tones there is a more serene atmosphere. Yellow on a clear or white background does not have a great expressive influence, while inverting the factors, yellow in the place of white, the expressive value changes completely. If we place a rose on yellow this takes on a greenish shadow and its original meaning is lost The purity of a love (the rose) cancels every meaning (knowledge, rationality) of yellow. Yellow and orange exalt together in the great canvasses of van Gogh. Yellow in a green field inceases its luminosity and it exalts even more in red and in viola while mixing with red-viola it loses its vigour. Yellow and blue can irradiate a cold light, while yellow on red is luminous, powerful, wise.

In general yellow gives us the sensation of sanctity and of deep religiosity: a desire to confession and purification. Yellow on black is, instead, lucid, abstract, inexorable, punitive.

The great stage erected in the San Paolo stadium of Naples for the visit of Pope John Paul II, a giant yellow screen with a sun of thin black rays expressed sanctity, but also a hidden sentiment of criticism for the work done up to then in the South of Italy. John Paul II, symbol of purity and love, assertor of religiousty as the only way to salvation, a new Savonarola for this corrupt country?

 

The chromatic pyramid

If for a moment we stop and consider the chemical structures which contribute to the pigmentation of tissues (skin, hair, feathers, tegumento) of the Vertebrates we notice that their number is limited to a few fundamental types: the black melanins, the dark red or brown pheomelanins, the yellow, red and blue carotenoids, the yellow flavines, the green or blue bile pigments, the white, yellow or red pterines and the white guanin.

Distributing the various pigments in the classes of animals one can built a pyramid which would indicate that with the evolution of the animals from fish to mammals the number of the chemical species of the pigmented cells is ever diminishing. Naturally, wishing to attribute a particular evolutionary role to the pigments the localisation of a flavine in the eye of the galago appears all the more extraordinary, and we ask ourselves how a porphyrin could finish up in the feathers of the turaco.

In men with red hair the skin is no longer protected from solar radiation, in that it is not able to synthesise melanin, and it is presumible, also taking into account the genetic pressure of the much more numerous races having melanocytes, that in man in the distant future the pheomelanins will no longer be present.

Also in the field of the biochromes man can be distinguished from the other animals and be placed alone at the apex of the pyramid.

 

 

BIBLIOGRAPHY

R.A. Nicolaus, Melanine, Quaderno dell’Accademia Pontaniana, N°.4, Ed. Giannini, Naples, 1984.

J. Itten, Arte del Colore, Il Saggiatore, Milan, 1965.

R.A. Nicolaus, Biogenesis of Melanins, Rassegna Medicina Sperimentale, Supp. 1, Idelson, Naples, 1962.

G. Misuraca, R.A. Nicolaus, G. Prota, G. Ghiara, Cytochemical Study of Phaeomelanins in Feather Papilae of New Hampshire Chick Embryo, Expermentia vol. 25, 290 (1969).

G. Prota, Progress in the Chemistry of Melanins and Related Metabolites, Medicinal Research Review, vol. VIII, 525-556, 1988.

J.P. Ortonne, Melanogenese 1989, INSERM vol. 201, 143 (1989).

R.A.Nicolaus, G.Misuraca ‘’  Colore 90  ‘’  Atti Accademia Pontaniana, XL, 83-107, 1991

R.A.Nicolaus, E.Novellino. G.Prota    Origine e significato del colore negli animali    Rend.Acc.Sci.Fis.Mat., XLII, 1-82, 1975.

R.A.Nicolaus, G.Scherillo,   ‘’  La melanina.Un riesame su struttura, proprietà e sintesi  ‘’  Atti Accademia Pontaniana XLIV, 265-287, 1995.

R.A.Nicolaus, A.Bolognese, B.Nicolaus,  ‘’ The pigment Cell and its Biogenesis ‘’  Atti Accademia Pontaniana, L, 225-243, 2002.

B.J.R.Nicolaus, R.A.Nicolaus,  ‘’  Speculating on the band colours in Nature  ‘’ Atti Accademia Pontaniana XLV, 367-385, 1997

G.Nicolaus, R.A.Nicolaus    Melanins, Cosmoids, Fullerens  ‘’  Rend.Acc.Sci.Fis.Mat., LXVI, 131-158, 2000. 

 

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Revised October 2003