THE PREPARATION OF OX-GALL AND ITS USES.
The preparation of ox-gall to be used in marbling is simple. Take a quart of fresh bile (ox-gall or fish-gall), place in a bottle which contains when filled from 1-1/2 to 2 quarts, add 1/2 pint of absolute alcohol, shake well and leave stand for from 14 days to 3 weeks. Within this time all particles of gum and all fatty substances which are present in some galls in comparatively large quantities, will fall to the bottom and the gall will be thin-fluid, pure and diaphanous, brownish, yellow or greenish according to the nourishment of the animal from which it was taken.
Cow-gall contains more gum and fatty substances, than ox-gall; fish-gall, on the other hand, is thinner than ox-gall and would be the most useful of them all, if it could be obtained in sufficient quantities. If the gall is thin and pure it is filtered through paper which is easily and quickly done as it runs like water. If by filtering the dregs of the gall the filter should become clogged, a new one must be used.
The addition of alcohol causes the precipitation of glutinous and fatty substances and preserves the gall from decomposition. If prepared in such a way it can be preserved for years without spoiling.
All colors which we intend to use for marbling must be bound to bodies absolutely insoluble in water; it is therefore a mistake to say, that the colors dissolve in water. You may grind the color on a marble slab or in a machine as long as you please, but you will only obtain a great degree of fineness of the bodies but never a dissolution of the same.
Each body possesses its limit of divisibility; in amorphous bodies the high divisibility is but natural, but in crystalline bodies this division must be produced by grinding or washing.
The gall does not combine with these bodies, nor does it penetrate them, but only clings to them loosely. It can be readily removed in case the colors should be rendered useless by the addition of too much gall. The color is allowed to precipitate in the bottle and the water standing above is poured off, fresh water is added and this manipulation is repeated several times.
The gall which surrounds every particle of color forms, as it were, the support of it and adapts it to float upon the size.
Bodiless colors, which give a complete solution with water will run into each other on being thrown on the size and will flow from the paper when it is lifted off. The insolubility of the color bodies therefore prevents them from running although they are disarranged on the size in drawing and although one color may be compressed or expanded by a second, yet they all remain separate without mixing, except, perhaps, that the shade of the first color becomes more intense, because its color particles are pushed together by the more violent expansion of the second color.
From this it will be seen that the colors, to be useful for our purposes, must be thoroughly insoluble. The gall is added during the process of grinding the color, so that the particles of colors are fully surrounded by the gall. The gall has an excellent effect on the colors but it also can act very injuriously if the necessary precautions are not taken. Carelessness is mostly the reason that the edges do not possess the demanded lustre of color and why they appear pale, as the marbler often uses the gall too soon when he notices the smallest obstacle, (due in most cases to the size.) It is therefore not astonishing that brilliant comb or peacock-edges are so rarely seen.
It is an obstacle to marbling, that the gall mixes so easily with the size. It often happens that the gall spoils the size before an edge was ever produced on it. This happens especially when the size on which the colors are prepared according to the old method, is too thick. The size is frequently soiled and spoiled when the colors are prepared, because the colors can not be perfectly drawn off on thick size. There will always remain some particles which will not only soil the size but impregnate it with gall, and which will cause the entire uselessness of size and color.
A very consistent size will make the preparation of colors extremely difficult, as they need a double quantity of gall for the purpose of spreading out. If there is but one color used, the preparation on such a size would be possible without spoiling it, but with four colors this is entirely impossible because the repeated drawing off of the colors, which always leaves particles behind, will, by and by, impregnate the size so that when the fourth color is prepared the first will not spread out any further.
The more the impregnation of the gall and size increases, the power of expansion of the colors decreases and this continues until both materials are useless.
It is therefore advisable, as I have already stated, in the chapter upon the varieties of sizes that the colors should be prepared separately on a small part of size to determine the correct consistency of the latter and to prohibit the whole size being soiled.
The gall should be kept in a small bottle containing about 1/10 quart with a perforated stopper from which a small tube protrudes and from which the gall can be added to the colors in drops.
Although the preparation of the color in this way takes more time, this trouble is amply repaid by the result.
Fatty bodies are injurious to the size, therefore they must be carefully avoided because they have the same effect as the gall, they form, although not insoluble in water, a combination with the size and prohibit the colors from spreading out. Fatty bodies can be transferred by glutinous fluids into a state of the most minute division and they then form emulsions.
Natural emulsions are milk, the yolk of egg, and the milky saps of plants. For this reason, in many establishments raw milk is used as a propelling medium for hair-veined edges.
There are also fatty bodies which, in an artificial way, form an emulsion even with water; for instance, almond, poppy and hemp, if they are ground to a pulp with a little water yield a milky mixture. All these emulsions artificial as well as natural, can be employed as expanding mediums and give better results for marbling than petroleum or naptha.
Substances Acting Similarly to Gall.
SUBSTANCES ACTING SIMILARLY TO
GALL.
There are rosins which are soluble in ammonia or borax. These solutions possess properties similar to gall and either can be used as an expanding medium or as an addition to colors. Different experiments with these solutions gave very good results.
To produce them pour a quart of water into a vessel, warm, add 2/5 of an ounce of shellac or rosin and a 1/100 part of a quart of ammonia or 2/5 of an ounce of borax so that the rosin becomes dissolved, and then bring the mixture to a boiling temperature.
Ammonia dissolves the rosins much more quickly and thoroughly than borax, but the solution in ammonia has the property of gelatinizing the colors after they have remained standing a short time. They therefore can only be used in a greatly diluted condition. The borax solution, on the other hand, has no such effect; not even the concentrated solution. I mention these two solutions especially, to instigate further investigations.