Painting Materials

A Short Encyclopedia

R. J. Gettens, G. L. Stout

• Publisher: Dover Publications
• Year: 2012
• ISBN:
  9780486142425
• Topic: Art
• Subtopic: Art Techniques

The combined training and experience of the authors of this classic in the varied activities of painting conservation, cultural research, chemistry, physics, and paint technology ideally suited them to the task they attempted. Their book, written when they were both affiliated with the Department of Conservation at Harvard's Fogg Art Museum, is not a handbook of instruction. It is, instead, an encyclopedic collection of specialized data on every aspect of painting and painting research.
The book is divided into five sections: Mediums, Adhesives, and Film Substances (amber, beeswax, casein, cellulose, nitrate, dragon's blood, egg tempera, paraffin, lacquer, gum Arabic, Strasbourg turpentine, water glass, etc.); Pigments and Inert Materials (over 100 entries from alizarin to zinnober green); Solvents, Diluents, and Detergents (acetone, ammonia, carbon tetrachloride, soap, water, etc.); Supports (academy board, dozens of different woods, esparto grass, gesso, glass, leather, plaster, silk, vellum, etc.); and Tools and Equipment.
Coverage within each section is exhaustive. Thirteen pages are devoted to items related to linseed oil; eleven to the history and physical and chemical properties of pigments; two to artificial ultramarine blue; eleven to wood; and so on with hundreds of entries. Much of the information — physical behavior, earliest known use, chemical composition, history of synthesis, refractive index, etc. — is difficult to find elsewhere. The rest was drawn from such a wide range of fields and from such a long span of time that the book was immediately hailed as the best organized, most accessible work of its kind.
That reputation hasn't changed. The author's new preface lists some recent discoveries regarding pigments and other materials and the pigment composition chart has been revised, but the text remains essentially unchanged. It is still invaluable not only for museum curators and conservators for whom it was designed, but for painters themselves and for teachers and students as well.

PIGMENTS AND INERT MATERIALS

Alizarin (alizarin crimson) (see also Madder) is the coloring principle of the madder root and it was first isolated from that source in 1826 by Colin and Robiquet (‘Recherches sur la Matière colorante de la Garance,’ Annales de Chimie et de Physique, 2d series, XXXIV [1827], pp. 225–253). It is 1,2 dihydroxyanthraquinone, and was first synthesized by two German chemists, C. Graebe and C. Lieberman, who reported their discovery in 1868 (‘Ueber Alizarin und Anthracen,’ Berichte der Deutschen Chemischen Gesellschaft, I [1868], pp. 49–51; see also English patent 3850, December, 1868). This is important in the history of organic chemistry, for alizarin was the first of the natural dyestuffs to be made synthetically. Its discovery caused the rapid decline and the almost complete disappearance of the large madder-growing industry in France. The ‘alizarin crimson’ lake used so extensively in artists’ paints is nearly all from this source. It is made with aluminum hydrate which gives a transparent lake; different shades of red can be made with different bases. It is more light-fast than natural madder lake because it contains none of the fugitive purpurin associated with alizarin from that source (see Eibner, Malmaterialienkunde, p. 202), and is among the most light-fast of the organic red pigments. Some painters have said, however, that synthetic alizarin does not give the pleasing, saturated, and fiery tone that madder alizarin gives. In ultra-violet light, synthetic alizarin does not give any of the strong fluorescence that is characteristic of madder lake. It may not be permanent when mixed with earth colors like ochre, sienna, and umber (see Toch, Paints, Painting, and Restoration, p. 97). Microscopically, alizarin lake is not readily distinguished. Merwin says (p. 517) that the isotropic base with the coloring matter has a variable low refractive index, about 1.70 for red. The color by transmitted light is purplish red. It is soluble and turns purple in dilute sodium hydroxide, but this behavior is hardly characteristic.

Alizarin Crimson (see Alizarin).

Aluminum Hydrate (transparent white), or aluminum hydroxide, Al(OH)₃, is a light, white material which is prepared by treating a solution of aluminum sulphate with an alkali such as soda ash or potash. The gelatinous aluminum hydroxide, because it adsorbs dyestuffs easily, may be used directly in pulp form as a base in the preparation of transparent lake pigments or it can be dried to a very light, white powder. This is used in paint manufacture, largely as a filler. It is the most common cheapening agent for artists’ oil colors and many of them now on the market contain it. Because of its low density and low refractive index, it lacks covering power and lends transparency to colors. It has high oil absorption and, for this reason, tends to increase yellowing in paints. Excess of it sometimes causes a rubbery consistency in prepared paste paints. Aluminum hydrate is difficult to detect in paint films by microscopic methods because of its lack of form and its lack of characteristic optical properties. It appears simply in clots of fine grains showing no birefringence. The hydrate is soluble in acids and alkalis, but is otherwise a stable material. When heated to a high temperature, it loses its combined water and is changed to aluminum oxide, Al₂O₃, which is of no value for pigment purposes. Alum and similar substances were used as early as classical times as a source of substrates for dye colors (see Bailey II, 233–238).

Aluminum Leaf and Aluminum Bronze Powder are made from sheet aluminum by a beating and a stamping process, respectively. The name, ‘bronze,’ is still retained, no doubt from its association with metal powders made from copper alloys (see Bronze Powders). Although aluminum powder was probably available as early as the middle XIX century, it was not until a decade or so after 1886, when aluminum began to be produced in large commercial quantities by the Hall process (see Aluminum, section on supports, pp. 221 and 222) that the powder became readily available. It was first used for coating picture frames and radiators. Aluminum powder did not become important as a pigment for commercial paints until after 1920 (see J. D. Edwards, Aluminum Bronze Powder and Aluminum Paint [New York: The Chemical Catalogue Co., 1927], pp. 26–29). Its development for outside and for protective painting followed experiments and field tests carried on in the Forest Products Laboratory, Madison, Wisconsin, and by the H. A. Gardner Laboratory in Washington.

When aluminum bronze powder is stirred into a suitable vehicle like oil or varnish, the flakes swirl and some come quickly to the surface layer where they spread out to form an almost continuous film of flat particles. This phenomenon, which is called ‘leafing,’ is caused by surface tension and is shown only to a marked degree by the polished powder and not by the unpolished powder (see J. D. Edwards, F. C. Frary, and Z. Jeffries, The Aluminum Industry, II [New York: McGraw-Hill Book Co., 1930], p. 803). No grinding of the powder and vehicle is necessary. In pyroxylin medium (nitrocellulose) aluminum powder has no leafing properties and does not form a durable film. Because of its leafing properties, it is now finding wide use for moisture- and waterproof paints. For exterior use, long oil spar varnishes are the best vehicle. Experiments at the Forest Products Laboratory show that this coating has outstanding moisture resistance and maintains its moisture-proofing efficiency over relatively long periods of time.

Aluminum bronze leaf in a vehicle has a reflectivity of 60 to 75 per cent for light, but it has low emissivity or radiating power for heat. At 40° C. the emissivity of aluminum paint is only about 20 per cent of that of a ‘black body,’ which is the theoretically perfect radiating surface (see Edwards, op. cit., pp. 47 and 51).

Microscopically, the particles of aluminum bronze powder are irregular in shape; in reflected light the individual flakes are lined with irregular, dark markings which are the result of having been stamped in contact with other flakes. Although the flakes are very thin (in the order of 1 micron), they are opaque to strong transmitted light.

Aluminum Stearate, Al(C₁₈H₃₅O₂)₃, is a soap made by the saponification of tallow and treatment with alum. It is a white powder which forms colloidal solutions or gels with linseed or other oils, turpentine, or mineral spirits. For this reason, it is often used in artists’ oil pastes and prepared paints to prevent separation of the oil from the pigment. Small quantities only are desirable because too much of it hinders drying and develops a ‘cheesy’ film. It is used also as a flatting agent in varnishes and lacquers (Gardner, p. 788). Because of its colloid-forming properties, aluminum stearate is not easily recognized in paints; it has no outstanding optical properties.

Anhydrite is the mineralogical name for native anhydrous calcium sulphate, CaSO₄, which is often associated in nature with calcium sulphate dihydrate or gypsum (see Gypsum). Although it has no useful setting properties, it occurs occasionally as an impurity in gypsum and plaster of Paris. Sometimes it is observed as a component of the gesso in Italian paintings. Anhydrite is a colorless inert like gypsum, but it differs from that material in the nature of its crystallinity and in its optical properties. It crystallizes in the orthorhombic system, has higher refractive index (β = 1.575) than gypsum, and is strongly birefracting. Particles of it appear as small, square tablets in gypsum gesso; it is characterized by cleavage in three rectangular directions (Dana, p. 630). The chemical properties are about the same as those of gypsum.

Aniline Pigments (see Coal-Tar Colors).

Antimony Oxide, Sb₂O₃, was introduced to the paint trade as a pigment under the trade name, ‘Timonox,’ in 1920 by the Cookson Lead and Antimony Co., Ltd, of England. It has good hiding power; the refractive index is about 2.20, nearly that of a reduced titanium oxide. Some commercial samples that have been examined (Merwin) were found to contain crystals which correspond to the two known mineral forms of antimony oxide: senarmonite, which is isotropic, and valenitinite, which is orthorhombic. They also contain some octahedral arsenic oxide as impurity. Antimony oxide is an inert substance to vehicles and its oil absorption is low (11.2 grams oil to 100 grams pigment [Gardner-Coleman]). Since it is darkened by hydrogen sulphide, it is usually mixed with zinc oxide, which has preferential absorption for that gas. Antimony oxide has not been mentioned specifically as an artist’s pigment, and it has no advantage over other white pigments.

Antimony Vermilion is antimony sulphide, Sb₂S₃; it may be prepared by precipitating antimony chloride with sodium thiosulphate or with hydrogen sulphide, and it may be had in hues varying from orange to deep red. It precipitates in minute isotropic red globules. It was first made by C. Himly in Kiel in 1842 (see Rose, p. 15). Although antimony sulphide figures as a pigment in the rubber industry, it is little used in paint because it is fugitive and not very stable chemically. It is said (Weber, p. 120) to have been used as an adulterant for real mercury vermilion. It is soluble in alkalis and in strong acids, and turns black on heating (Rose, p. 16).

Antimony Yellow (see Naples Yellow).

Antwerp Blue (see Prussian Blue).

Armenian Bole (see Bole).

Artificial Pigments (see Synthetic Pigments).

Arzica (see Weld).

Asphaltum (bitumen) is a brownish black, native mixture of hydrocarbons with oxygen, sulphur, and nitrogen, and often occurs as an amorphous, solid or semi-solid liquid in regions of natural oil deposits. It is thought to be formed from the evaporation of the lighter components of the petroleum and from polymerization and partial oxidation of the residue. It is found widely, but that used in European paintings came, perhaps, from the region of the Caucasus or the borders of the Dead Sea. In Mesopotamia and Egypt in very early times it was known and used for various purposes (see Partington, index). Asphaltum has little use now, but is still listed by artists’ supply dealers. Not much is known about its preparation, but Church says (p. 235) that the crude asphaltum is usually heated to a fairly high temperature to drive off moisture and volatile materials before it is ground in oil or other mediums. The pigment is partially soluble in oil, like a stain, and gives a semi-transparent, reddish brown film. In the film, it may be occasionally observed microscopically as tiny brown flakes without structure. Only thin grains are transparent brown. It is soluble in turpentine, naphtha, and other organic solvents.

Asphaltum and other similar tarry compounds are among the least desirable pigments known because they never become permanently dry. In thick oil films, they have a tendency to run and to crawl, but, if they are properly prepared, such difficulties may be partially overcome (see Church, p. 236). Doerner says (p. 189) that Rembrandt used asphaltum as a glaze with no harmful effect. It is unaffected by acids and is unsaponifiable; it requires about 150 per cent of oil to grind. Under ordinary circumstances, it is unaffected by light but is faded by strong exposure. It was much favored by the XVIII century English school, with unfortunate consequences; those paintings which contained it have become disfigured because of shrinkage of the paint films and ‘alligatoring.’ Harder paint films put over it sometimes crack and curl. Neuhaus says (see footnote in his translation of Doerner’s The Materials of the Artist, p. 89): ‘Under high summer temperatures in museums without thermostatic control whole areas of the picture surface have moved and become permanently dislocated. Thus in several warm climatic belts of America it has caused the destruction of many paintings of the Munich school which at one time was passionately fond of asphaltum as a frottie.’

Asphaltum is also sold to the artists’ trade under the name ‘bitumen.’ Both mummy (see Mummy) and bistre (see Bistre) are similar in color and composition to asphaltum in that they are tarry, organic substances, but their origin is quite different.

Aureolin (see Cobalt Yellow).

Azurite (mountain blue) is a natural blue pigment which is derived from the mineral, azurite, a basic copper carbonate, 2CuCO₃.Cu(OH)₂. The mineral occurs in various parts of the world in secondary copper ore deposits where it is frequently associated with malachite, a green basic carbonate of copper (see Malachite ). Like other mineral pigments, this has been prepared from carefully selected material by grinding, washing, levigation, and flotation (see Thompson, The Materials of Medieval Painting, pp. 131–132). It has long since ceased to be of importance in Western painting, and is rarely used today, except perhaps to a limited extent in the East.

Azurite is crystalline and is fairly highly refracting and birefracting. For use as a pigment, it is ground rather coarsely because fine grinding causes it to become pale and weak in tinting strength. Ninety-mesh azurite, however, is deep violet-blue in color. Areas of dark azurite on paintings can often be recognized by their sandy texture and by their thickness. Traditionally, it appears to have been most used in a tempera medium because in oil it would be dark and muddy and would not have the sparkle that it has in tempera. The characteristics of azurite blues in old paintings are well described by Thompson (loc. cit., pp. 132–135). The penetration into azurite paint in European panel paintings of successive layers of oil and varnish films has often caused such areas to become nearly black. If cleaned, the particles are usually revealed unchanged. Although there may be instances where the pigment has turned green (to malachite) by hydration, the more usual cause of the change in color is the optical effect of superimposed layers of discolored varnish. Azurite is blackened by heat and by warm alkalis, and it is soluble in acids, even in acetic acid; but, under ordinary conditions, it appears to be a remarkably stable pigment.

This natural copper carbonate was no doubt the most important blue pigment in European painting from the XV to the middle of the XVII century and in paintings of that period it is found more frequently than ultramarine. De Wild (p. 23) lists nineteen early Dutch and Flemish paintings on which he identified azurite. Europe had various sources of the mineral. There is evidence (see Laurie, New Light on Old Masters, p. 42) that Hungary was the principal source in the XVI century, but the pigment disappeared from the painter’s palette in the middle XVII century when Hungary was overrun by the Turks. One of the early names for azurite was azure d’Alemagna, indicating that it came from Germany. It is the azurro della magna of Cennino Cennini, and was known by numerous other names in mediaeval times (see Thompson, ’Trial Index for Mediaeval Craftsmanship,’ p. 415, f.n. 4 and 5).

Azurite was the most important blue pigment in the wall paintings of the East. It was employed in the cave temples at Tun Huang in Western China and was used lavishly in wall paintings of the Sung and Ming dynasties in Central China. With difference in the fineness of grinding, different shades were produced (see Gettens, ‘Pigments in a Wall Painting from Central China’). The source of azurite in China is not known, but there are extensive copper deposits in the provinces of Kwei-chou and

lists azurite...