A technical dictionary of printmaking, André Béguin.
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gums and resins

Gums are viscous substances which are secreted by the bark of certain trees. Usually transparent (but sometimes slightly tinted) they contain a mucilage which when dissolved in water makes the latter become viscous. When this mucilage is dissolved in water it can be made to precipitate with alcohol.
Resins, on the other hand, are gluey and viscous substances which may be whiteish, brownish, or red and are secreted by certain trees when they are incised. Resins contain an essence and are usually not water soluble.
Gum resins are mixtures of the above, balms or balsams are pasty resins, and pitch is made up of a mixture of resins.
All of the abovementioned substances are similar to the various waxes even though they are often harder than waxes. These substances are all natural. Artificial resins, on the other hand, are synthesized in a variety of ways. Artificial resins are used in the making of inks, paints, etching grounds, and plastics. They are derived from colophony, bakelite, urea, glycerine, silicon, and vynil.

1. GUMS.
A. GUM ARABIC. Gum arabic is the most commonly used gum in printmaking. This gum is exuded by certain exotic trees. The best gum arabic is gum senegal, which is taken from the Vereck acacias. Gum can be bought in hard blocks that are light yellow in colour and are translucent (at times they are almost colourless). It also comes as a powder or in a water solution (gum arabic glue). Under the same name of gum arabic goes a darker substance that is harder and more breakable than real gum arabic. This other type of gum should not be used in preparing lithographic work and above all not on gum bichromate copies. This second type of gum arabic can be recognized from its very intense viscosity.
Gum arabic is a potassium and calcium salt of arabic acid ( arabine) which is easily dissolved in water since it will absorb its own weight of water. However, as it is difficult to dissolve it entirely when it is in pieces, it is better to buy it powdered. If it is not in powdered form and it contains some impurities it must be put in a bag of cheese-cloth and suspended in the water. Only the bottom part of the bag must be in the water and it must not touch the bottom of the container. The bag should be kept in the water overnight. The solution must usually be corrected until it reaches 14B as measured with an hydrometer, in which case its consistency will be "creamy". This concentration (14B) can be had directly by putting 400g of gum arabic in 1 liter of water (4 parts gum arabic to 10 parts water, by weight), but often some water must still be added after the gum has dissolved. Wait some 12 hours before measuring the concentration. It may be necessary to filter the solution through several layers of cheese-cloth.
Solutions of gum arabic and water can ferment, form moulds, and become acid, thus making them unsuitable for use. This is especially true if the solution is to be used for lithographic preparing since it will attack the lithographic surface rather than protect it. In order to avoid these problems one must add an antiseptic, one of the best being salicilic benzyle (1 g per liter - 0.035 ounces per 1.75 pints), which should be dissolved in a bit of methylated spirit before being mixed into the gum arabic solution. One can also add 1 cm3 of formaline or phenol.
Insofar as concerns the uses of gums arabic in preparing the lithographic surface, in metallography, and in preparing the light sensitive surface in photography, turn to the articles on lithography and on photographic processes.

B. RUBBER, LATEX, or INDIA RUBBER. The coagulated sap of various tropical trees. It can be dissolved in heavy benzine to obtain a thick plate which is then thinned with cristallizing benzine. Rubber is used to reinforce collodion light-sensitive surfaces [photographic processes], to make moulds in galvanic processes , as a support of photographic copies in one of the galvanic processes, and as a blanket cylinder. Rubber ink is used in silkscreen work when drawing an image directly onto the screen [ink, guttapercha]

2. RESINS.
A. COPAL. This type of resin is produced by tropical trees which are mostly found in Madagascar. Real copal is hard. There are other types of copal which come from Brazil and from the USA but these types of copal are softer (they are made from a type of sumac) and are of lesser quality. Copal is used in graining in aquatint, in various galvanic processes, and, in particular, in making hard grade lithographic crayons.

B. COLOPHONY. Colophony is made by distilling pine tree resin. It is a by-product of turpentine oil. The latter being more fluid flows downward leaving behing the resin. There are three commercial grades of colophony: colourless (WW), very pale (N), and brownish (K). The brownish grade is made from resin tar or from the pasty residues of the distilling process and is often used even though it is of bad quality and "cooks" very quickly. "K" quality colophony is perfect when used on zinc plates as they need not be heated very much. However, it is not advisable to use it on aquatint plates. Colophony is also used to protect the biting ink in gillotype work. The graining of aquatint plates in a dust box must be done with colophony since the resin clumps at the slightest humidity. Various types of colophony are used in manufacturing varnishes, grounds, and to make transfer ink used in lithography. Colophony is soluble in alcohol, acetone, and oil of turpentine.

C. LAQUER. This resin is produced by Japanese lacquer trees and by sumac trees in the Far East when they are punctured by certain parasitic insects. Lacquer is reddish brown when On the tree. Commercially it is available in sticks, its usual shape, and in drops (when it falls spontaneously from the tree), but also in flakes or in plates which is called shellac (in both cases the lacquer has been melted down. Lacquer may also come in a more or less refined form of yellow or white lacquer. It is soluble in alcohol and methanol. Lacquer is used to make beautiful varnishes and, when bichromated to make copies on metal plates.
When lacquer is used for photographic purposes such as the one just mentioned best results will be obtained with a wax-free lacquer. Dissolve lOOg of lacquer in 250ml of dehydrated methylated spirit.
This is done either cold or heated slightly in a double-boiler. After cooling pour the solution into a glass container (capable of containing more than 2 liters) in which has already been prepared a solution of 16g of caustic soda in 800 ml of water [photographic processes ]. Lacquer is also used in making both lithographic and autographic ink.

D. SANDARAC or GUM JUNIPER. An odorous resin produced by certain species of thuya. It is usually sold in the form of white powder. Sandarac is used in drawing where it can replace the finish of paper to forestall an excessive absorption of ink. The sheet of paper is dusted with this resin and then rubbed softly.
Although sandarac is more expensive than colophony it is usually preferred over the latter when using dust boxes for graining aquatint plates and for manual photogravure plates because. it is less sensitive to humidity. Sandarac is also used in the making of etching grounds.

F. DRAGON'S BLOOD or GUM DRAGON or TRAGACANTH. "The fruit (of the calamus draco palm tree) looks so much like a dragon that a painter might have drawn it." This is what Laurens Catalan wrote in 1634 when discussing the legend related by Pliny whereby a dragon sucked the blood of an elephant in order to cool the fire burning in its entrails.
Actually dragon's blood is a resin made up of various red resins coming from Central and South America, from the Azores, and from the Far East which are soluble in alcohol, benzine, and turpentine oil. Dragon's blood is an expensive resin used to colour fine varnishes. It is also used for reinforcing the protective ink which prepares photo-engraving plates for etching [ photo-engraving] or for successive etchings.
Dragon's blood is also used in making autographic ink.

F. GUM MASTIC or MASTIC is a resin which exudes from the levantine turpentine-tree. In drop form mastic is pale yellow in colour whereas in pieces it is rather brownish. Both are soluble in turpentine oil, in benzene , and in carbon tetrachloride. Mastic is used in many etching grounds and in lithographic ink where it is always used in drop form.

3. VENICE TURPENTINE.
A syrupy, translucid, and greenish or yellowish liquid obtained from larch trees. This kind of turpentine can be considered a kind of resin. It is soluble in alcohol, ether, and chloroform and is used in the making of lithographic ink. [solvents].

4. PITCHES.
Pitches are often used in making etching grounds. Some of the more commonly used pitches are black pitch, Greek pitch and, above all, Burgundy pitch. Burgundy pitch is a yellowish and gluey mass obtained from spruce firs. It is softened with ceresine which is a mineral product resembling paraffin. Black Swedish pitch is used in making ink that resists biting (as was Burgundy pitch in the past). Syrian asphalt has also been called "pitch" at times.
[oils, etching_grounds, solvents].


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