GLUES - GELATINS
N.B. In English language glue and adhesive are not interchangeable; glue refers to the natural product (aqueous) while adhesive usually refers to a synthetic product (i.e. n on aqueous).
Glue is an organic colloidal substance of varying appearance, chemical constitution and physical properties. Prepared from animal products: sinews, bones, skin, cartilage, tendons, hoofs; most contain collagen (gelatin and chondrin). Collagen (or ossein) under the influence of boiling changes into gelatin. Overcooking, however will destroy ability to gel upon cooling. Chondrin is obtained from skin, tendons and bones.
Short historical overview
Egypt: glue was found in the tomb of Queen Hatshepsut XVIII B.C. Pliny refers to glue as one of the vehicles for painting of ancient Egyptians, even the Bible mentions glue in Ecclesiastes: He that teachet a fool is like one that glueth a potsherd together. During the Middle Ages glue is used extensively, in addition to other media (glair and egg tempera) for manuscript illumination. During the Early Renaissance (especially Flanders and Germany) glue is used for the execution of a so-called "Tuschelein" paintings. The medium was a type of distemper: a mixture of dry pigment and size (glue) as a binder.
Manufacturing: . The earliest practical manufacturing of glue occurred in Holland in the 17th century (during the reign of William III). . Shortly afterwards it was introduced in England (1700) and in France (Lyon) which were the major factories of this kind in Europe.
Desirable properties: viscosity, jelly strength and adhesion. A glue to be acceptable as artist’s material should be pale in colour, free of fats, pH neutral (around 7, but never under 5.5 or above 8, good glue is pH 6.7-7), foam as little as possible and not have unpleasant odour.
Problems: glue is hygroscopic and it will swell and shrink according to the RH. It is also susceptible to mould growth and insect attack. Some additives will alter the glue’s behavior. Alum (potassium alum sulfate KAl(SO4)2•12 H20) will increase viscosity and the presence of common salts will ensure that glue remains liquid when cold. In old workshops urine was added with the same results. Glue is an ideal nutrient for bacteria and will putrefy rapidly. Fetid glue liquefies by its own acid decomposition products. Fetid glue is of no use as a binder, or for gesso, but is often used by gilders as a gilder’s liquor.
Gelatin is a pure form of glue formed by heating collagen (80°-90°C), which is the major ingredient of bones, cartilage, tendons and skin. It is a nearly colourless, transparent, amorphous substance. In its normal dry state (c. 15-18% H20) is flexible and horny. Precipitated from alcohol or salts it is white and water free. Gelatin is typical colloid and it swells to many times its normal volume when immersed in water. Starts to dissolve at 40°C , above 70°C it starts to decompose and its adhesive qualities are greatly reduced.
Rabbit Skin Glue (RSG) is made from skins of rabbits or hares. It shows great flexibility, although it has a slightly poorer adhesive properties than bone glue. Originally made in France from skin clippings - a by-product of felt industry.
The most widely known manufacturers are TOTIN FRERES-PARIS, whose seal is impressed in each of their glue tablets.
Parchment glue is made from parchment clippings, also glove cuttings. And is considered as a finer type of glue.
Isinglass glue is a gelatinous semitransparent substance obtained by cleaning and drying the swimming bladders of sturgeon, cod, hake, and other fishes. Isinglass is obtained mainly from Russia, but also from the United States, Canada, Brazil, Indonesia, the West Indies, and the Philippines. It is rather costly and mostly used when gilding directly on glass. It is the most flexible of all types of glue and was valued by ancient icon painters.
Casein, an organic compound belonging to the class of proteins. It is a valuable medium used by painters for centuries. Like most proteins it is amphoteric - it functions as acid and as base. Casein is prepared from skimmed milk which is heated to c. 30°C and to which hydrochloric acid is added which precipitates calcium caseinate. Mixing milk curds with alkali such as lime yields one of the strongest glues used since Antiquity. Casein powder: only finely ground lactic acid casein is suitable for painting. Used in wall painting as fresco secco and as casein tempera it becomes non-soluble upon drying. Sometimes it is added to egg tempera to increase the insolubility.
GUMS
Term: “gums” is applied to a number of non-crystalline, structurless substances, of vegetable origin (exudations of trees and shrubs). They consist essentially of hydrates of carbon and are either soluble in cold water, or swell in water if left for some time (resins neither dissolve, nor swell in water, hence the designation such as "gum mastic" is a misnomer and confusing). Gums are insoluble in alcohols and do not melt (like resins) upon heating, but char. Historically gums were most likely used for a very long time. Theophilus Presbyter (approx. 1070-1125) gives an account of usage of gum instead of sun-dried oil in his treatises Schedula (Hawthorne, J.G. and C.S. Smith, Theophilus: On Divers Arts, University of Chicago Press, 1963; reprinted New York: Dover Publications 1979).
Gum arabic
Gum produced by several species of acacia growing in North America, Sudan and Senegal. The best grade for artists' use is from Senegal: Acacia Senegal (grows to 20ft in height). A better grade is obtained from cultivated trees, than from the natural which exhibits better density and adhesiveness and contains a smaller amount of mineral impurities. Chemical composition: arabin; a mixture of arabic acid salts and free arabic acid (C12H22O11). Gum arabic is marketed in form of “tears”, which are colourless or slightly yellow/reddish lumps and break with vitreous fracture. Resin does not and therefore this too is a way to distinguish one from another. Gum arabic dissolved in cold water should not leave any residue.
Common recipe: 1 part/volume of gum to 2 p/vol of water, left to dissolve overnight. This is a stock solution, which may be diluted as needed. Gum solutions tend to turn sour, and commercial made gum arabic contains preservatives.
A. H. Church (The Chemistry of Paints and Painting, London, 1915, p.93)recipe: 28 gr of gum dissolved by slowly adding to 54 mil of boiling water. When all is dissolved the liquid is left to stand for a day and decanted. (A small amount of antiseptic/fungicide may be added).
Strasbourg MSS 14/15th cent. recipe: Powder 1/2 oz (14 gr) of gum arabic. Pour water over it (one finger deep) and leave overnight to soften. Mix, add white myrrh* (one setit). The medium should be as thick as oil. (V.& R. Borradaile, The Strasburg manuscript, a medieval painters handbook, Verlag Georg D.W. Callwey, Munchen, n.d.
* Myrh is obtained from species of Commiphora type of bush, native to North Africa, which yields a reddish-brown oleo-gum-resin that has antiseptic properties.
Gum tragacanth comes from thorny shrubs of genus Astraghalus that grow mostly in Greece, Crete, Iran and Asia Minor. Unlike gum arabic it must be wetted by alcohol before it can be dissolved in water. Chemical composition: carbon, hydrogen & oxygen of complex constitution called bassorin. The gum consists of: starch, cellulose and a large portion of mucilage, which swells in cold water, but does not dissolve, thus must be strained through a cloth. Only 2-3% of gum makes a fairly thick solution. Gum tragacanth has unique properties: it does not contain a great binding strength on its own, but it can bind 8-10X as much pigment as gum arabic therefore is sought after as a major binder for pastels and crayons. It is quite more expensive than gum arabic.
MODERN BINDER: Methyl Cellulose
If cellulose is changed to methylcellulose a water soluble adhesive is formed. Cellulose methyl ether is produced by treating cellulose from wood or cotton with an alkali, such as sodium hydroxide, followed by methyl chloride. The resulting product is a white granular solid, soluble in cold water but insoluble in hot water. It is used as a thickening agent for aqueous preparations and as a substitute for natural gums, and particularly as a stabilizer in emulsions. But because it is very easy to achieve a smooth, even paste it has become very popular.
Recipe/preparation: place powder to swell in cold water (methyl cellulose will NOT dissolve in hot water), for 1-15 min, shake vigorously in the jar. The result is translucent, viscous "paste" that may be thinned with water. It is a major modern binder for pastels for which solutions of different strength/concentration are prepared. The choice of solution will depend upon the type of pigment/inert filler used.
M-1 (stock) solution: 350 ml cold water + 7 gr methyl-cellulose. Let stand overnight!
M - 2 solution: 175 ml of M-1 solution + 350 ml of water
M - 3 solution: 175 ml of M-2 solution + 350 ml of water
M - 4 solution: 175 ml of M-3 solution + 350 ml of water
M - 5 solution: 175 ml of M-4 solution + 350 ml of water
RECIPES – PASTELS: Mix dry ingredients first. Add gradually the liquid until stiff paste is achieved. Roll into shape between absorbent paper and leave to dry.
Recipes for certain pigments are given in: Watrous, The Craft of the Old Masters, Madison, Wisc., 1957
Raw Sienna or Yellow ochre: 1 measure dry pigment, 1 measure ball clay, water
Burnt Sienna: 1 measure dry pigment, 1 measure kaolin/ball clay, M-2 solution
Burnt Umber: 1 measure dry pigment, 1 measure calcium carbonate (whiting), water
Titanium White:1 measure dry pigment, 1 measure ball clay, water
Black I: 1 measure Mars black pigment, 1/4 measure ball clay, water
Black II: carbon black dry pigment, gum arabic solution (1 oz gum arabic: 8 fl. oz. water)
Black III: carbon black dry pigment, starch solution (1/4 oz starch: 8 fl oz water)
Venetian red: 3 measures dry pigment ("Light Red"), 1/8 measure kaolin, water
CRAYONS
A great ambiguity exists in the use of the term “crayon’ as it is applied to a variety of materials and implements. (see Blog on: Chalks: red, black and white) Ideally the term “crayon” should refer to a colour stick made either with oily, waxy or greasy binding medium. It is the “fattiness” that distinguishes crayons from pastels. Historically it is difficult to establish the beginning of crayon production. The earliest reference can be found in Leonardo’s manuscript, but since Leonardo experimented with many different techniques and materials this does not necessarily suggest a wider usage.
Basic recipes: RED CRAYONS (will resemble the modern conté)
I. 1/ Mix the following ingredients while in dry state (ratios are given in “volume”):
2 measures burnt sienna dry pigment, 1/2 measure cadmium red, 1/4 measure Venetian red, 3 measures ball clay (or kaolin)
2/ Grate 7 grams of a good dry soap (Ivory). Dissolve it in 30 mill. of warm water to obtain a creamy consistency (All flakes must be dissolved completely).
3/ Mix dry materials and soap solution into a paste and roll into cylinders.
II.
1/ Soak 1 gr. of powdered gum arabic in 1 tsp of water.
2/ Soak 71/2 grams of grated soap (IVORY) in a 1 tsp. of water.
3/ Mix the liquid ingredients together and add 28 gr. of Venetian red dry pigment to form a paste.
FOR FATTY CRAYONS:
BLACK
Melt together over a low heat 28 gr of tallow (beef fat), 14 gr of pure beeswax
Take 14 gr of tallow/beeswax mixture and add 1 to 2 tsp of turpentine. Warm it over a low fire until it has melted and the turpentine is thoroughly incorporated. Add 28 gr of ivory black dry pigment> Mix it well and pour it into a metal or porcelain mould to harden.
RED: as above, but replace the black pigment with “Venetian red” (red earth)
Thursday, November 26, 2009
Rubeniste vs. Poussiniste controversy
To answer the proverbial question: What was first, the drawing or the painting? one has to search within the human's earliest pictorial expressions. The Paleolithic caves of Altamira, Lescaux and others are profusely decorated with images of animals as well as "abstract" pictograms. The images of animals are presented as a simple outline, most likely done with a piece of carbonized twig, or are coloured in with various shades of naturally available clays (i.e. earth pigments). If these example can be applied to answer the posed question than one has to concede that both modes of expression existed side by side commanding equal importance.
The schism between drawing and painting regarding their importance was more apparent during the Medieval times when drawings seldom existed as an independent artistic work, satisfying mostly a utilitarian character. They illustrated various daily implements or simple contraptions, or were used as a starting point for a more ambitious painting or sculptural projects. Preliminary drawings were often submitted to a patron before contracts were signed for larger commissions. During the Renaissance the status of the drawing dramatically changed; it slowly evolved from the subordination to the other forms of art and took on a more elevated and independent character.
The other question equally debated and equally difficult to answer was: What is more important design or colour?
Giorgio Vasari (1511 –1574) divides his Lives of the Most Excellent Painters, Sculptors, and Architects into disegno and colore and the excellence in disegno was considered a goal… to which every artist should aspire to. This was further expounded by the rivalry between the School of Venice to which colore was ascribed as a major force, and the school of Tuscany for which drawing was the underlying force. Vasari didn’t completely disregard artists that were colorists, but still considered the drawing as more intellectually challenging and requiring more skill. His views will inadvertently shape the opinions of art critics throughout the history of art, practically to the time of the Impressionists.
Rubénistes vs Poussinistes
The two factions Rubénistes and Poussinist took their names after painters Peter Paul Rubens(1577-1640) and Nicolas Poussin (1594-1665). Rubenistes advocated that colour is the essence of life and nature and at least of equal importance to the design. The Poussinistes considered that the intellectual appeal of a painting was afforded by the presence of clarity, logic, and order, inspired by the classical art from Greek and Roman antiquities. The great controversy developed in France in 1670's and culminated during the mid-1800s. The establishment, the Academy, sided with the Poussinistes and promoted the supremacy of draughtsmanship and design over the painting. However the Rubenistes triumphed with the acceptance in 1712 of Watteau, a supreme colourist, as a full member of the Academy. Moreover his special style was recognized by giving it a particular term: fêtes galantes.
An overall acceptance of colour by artists and public alike didn’t also include a scientific understanding how it actually stimulates our senses, nor how different colours interact one upon another. Until practically nineteenth century it was considered that every object has a 'true' colour and little attention has been paid to other influences, such as different illumination, interaction of colour, physical distance of objects etc.
In 1839 a very important work was published: The principles of Colour Contrasts, by Michel Eugène Chevreul (1786-1889), Professor of Chemistry at the tapestry makers Manufacture des Gobelins. (see: Birren, Faber, History of Colour in Painting, Van Nostrand Reinhold, N.Y. 1965). This seminal work basically expressed, what painters knew intuitively: the greatest colourists have always obtained the maximum brilliance with a minimum of colour. John Ruskin (1819-1900) further postulated that in a painting one can change a certain colour by altering its surround rather than actually modifying it.
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