“Gelatine should never be judged by the eye alone.
“Its purity may be very easily tested thus: Soak it in cold water, then pour upon it a small quantity of boiling water. If pure, it will form a thickish, clear straw-coloured solution, free from smell; but if made of impure materials, it will give off a very offensive odour, and have a yellow, gluey consistency.”
WASHING
When there are stains or ink marks on books that cannot be removed by the use of hot size or hot water, stronger measures may sometimes have to be taken. Many stains will be found to yield readily to hot water with a little alum in it, and others can be got out by a judicious application of curd soap with a very soft brush and plenty of warm water. But some, and especially ink stains, require further treatment. There are many ways of washing paper, and most of those in common use are extremely dangerous, and have in many cases resulted in the absolute destruction of fine books. If it is thought to be absolutely necessary that the sheets of a book should be washed, the safest method is as follows:—Take an ounce of permanganate of potash dissolved in a quart of water, and warmed slightly. In this put the sheets to be washed, and leave them until they turn a dark brown. This will usually take about an hour, but may take longer for some papers. Then turn the sheets out and wash them in running water until all trace of purple stain disappears from the water as it comes away. Then transfer them to a bath of sulphurous (not sulphuric) acid and water in the proportion of one ounce of acid to one pint of water. The sheets in this solution will rapidly turn white, and if left for some time nearly all stains will be removed. In case any stains refuse to come out, the sheets should be put in clear water for a short time, and then placed in the permanganate of potash solution again, and left there for a longer time than before; then after washing in clear water, again transferred to the sulphurous acid. When sheets are removed from the sulphurous acid they should be well washed for an hour or two in running water, and then may be blotted or squeezed off and hung up on lines to dry. Any sheets treated in this way will require sizing afterwards. And if, as is often the case, only a few sheets at the beginning or end of the book have to be washed, it will be necessary to tone down the washed sheets to match the rest of the book by putting some stain in the size. For staining there are many things used. A weak solution of permanganate of potash gives a yellowish stain that will be found to match many papers. Other stains are used, such as coffee, chicory, tea, liquorice, &c. Whatever is used should be put in the size. To ascertain that the right depth of colour has been obtained, a piece of unsized paper, such as white blotting-paper, is dipped in the stained size and blotted off and dried before the fire. It is impossible to judge of the depth of colour in a stain unless the test piece is thoroughly dried. If the stain is not right, add more water or more stain as is needed. Experience will tell what stain to use to match the paper of any given book.
To remove grease or oil stains, ether may be used. Pour it freely in a circle round the spot, narrowing the circle gradually until the stain is covered. Then apply a warm iron through a piece of blotting-paper.
Ether should only be used in a draught in a well-ventilated room on account of its well-known inflammable and anæsthetical properties.
A very dilute (about one per cent.) solution of pure hydrochloric acid in cold water will be found to take out some stains if the paper is left in it for some hours. When the paper is removed from the solution, it must be thoroughly washed in running water. It is important that the hydrochloric acid used should be pure, as the commercial quality (spirits of salts) often contains sulphuric acid.
The following recipes are quoted from De l’organisation et de l’administration des Bibliothèques, par Jules Cusin:—
To remove stains from paper:—“Mud Stains.—To take away these kinds of stains, spread some soap jelly very evenly over the stained places, and leave it there for thirty or forty minutes, according to the depth of the stain. Then dip the sheet in clean water, and then having spread it on a perfectly clean table, remove the soap lightly with a hog’s hair brush or a fine sponge; all the mud will disappear at the same time. Put the sheet into the clear water again, to get rid of the last trace of soap. Let it drain a little, press it lightly between two sheets of blotting-paper, and finish by letting it dry slowly in a dry place in the shade.
“Stains of Tallow, Stearine, or Fat.—To take away these stains cover them with blotting-paper and pass over them a warm flat-iron. When the paper has soaked up the grease, change it and repeat the operation until the stains have been sufficiently removed. After that, touch both sides of the sheets where they have been stained with a brush dipped in essence of turpentine heated to boiling-point. Then to restore the whiteness of the paper, touch the places which were stained with a piece of fine linen soaked in purified spirits of wine warmed in the water-bath. This method may also be employed to get rid of sealing-wax stains.