(5) When shellac is part of the mixture, it is vital to burn the mass well, as only thus will shellac dissolve properly.
Shellac, which is made in China and East India from an insect belonging to the bee family, will melt under moderate heat, but will not dissolve in any animal fat or oil unless it has previously lost its inherent acid, which occurs only under combustion. If shellac is melted with oil or fat, it covers the bottom of the vessel in the beginning. With heat increased till it causes combustion, it begins to swell, rises to the surface, and at last covers the surface in the form of a spongy mass. If the heat still increases, it begins to dissolve into foam. Then it is time to remove the mass from the fire and to cover it with a tight lid, that the flame may be extinguished.
If shellac has been once melted and has hardened, it dissolves only slowly even under severe combustion. It is better, therefore, to bring the other substances to combustion first, and then to mix the shellac in small portions, which will dissolve much more readily because they will be attacked by the great heat in the moment of melting and will not have time to swell first and get hard.
As soon as the mass has cooled a little, the second part of soap is added, and the whole heated, without burning, merely enough to melt the soap.
(6) None of these mixtures can be kept well any length of time in fluid form, that is, dissolved in water, because it becomes slimy after a very few days, sometimes sooner. It can be liquefied again by mixing with water, but not without affecting its durability. Therefore the ink must be stored dry, in which form it lasts for years without change. When required, a small quantity, about the size of two peas, is rubbed down in a very clean small earthen or porcelain vessel, such as a saucer. Those mixtures that contain tallow rub the easiest. The others, containing harder substances, require more pressure. The ink should be spread evenly over the bottom of the vessel. Then a coffee-spoonful of rain or other soft water is poured in, and the mixture is rubbed with the finger till the solution is perfect. Then it is put into a small, very clean pot of glass or porcelain and is ready for use.
(7) A great deal depends on the proper quantity of water. A good ink must be completely dissolved, with no solid particles left. It should be about as fluid as a good, fat milk or vegetable oil. If it is too thick, it makes the work difficult. If it is too thin, it will not withstand the etching fluid. A few experiments will teach the proper proportions. Even a good ink will make poor lines if it is laid on too thinly and not firmly enough. This, however, is due to the artist's lack of skill or to defective pens, of which I will treat hereafter.
With this quantity of ink it is possible to work for a whole day. Thus each day fresh ink can be mixed; and it is to be noted that the vessels must be cleansed scrupulously that no trace of the previous day's ink be left in them. The ink will dry during the work, and as soon as this begins to interfere with its use, one or two drops of water will thin it again sufficiently.
This is about all that need be said about the chemical fatty or alkaline stone-ink in general. Particular remarks will be found in the description of its use for particular methods.
II
HARD BORAX INK
Besides the inks described, it is well to make the following and keep it in stock for uses whose great value will be explained later.