Perhaps it is hardly necessary to say that your first experiments should be made upon books of no value whatever, preferably volumes that have been picked out of the penny tub for this purpose. You will also have procured (if indeed you do not already possess) a copy of Mr. Douglas Cockerell's invaluable little book which I have already mentioned, and have studied it as has been suggested above. Mr. Zaehnsdorf's work also contains a chapter on this subject.
The paraphernalia required are not numerous or expensive, for they consist merely of three or four wide-mouthed glass-stoppered bottles in which to store your chemicals, and a few photographer's developing dishes (the deep ones, of white porcelain) of a suitable size for octavo, quarto, or folio leaves.
Obviously the first thing to do is to remove from the book the leaf or leaves that require cleaning. Unless, like Gerard de Leew, the Antwerp printer, you are 'a man of grete wysedom in all maner of kunnyng,' you will not attempt to clean the leaves of a book in situ. In fact he would be a very brave (or foolish) man who, without great experience, tried to remove any sort of stain from a page without removing the leaf first of all. Our own experience is that it is better to pull the whole book to pieces—or rather take it to pieces, for the word 'pull' in this connection makes one shudder. Carefully cut the threads that hold the quires to the bands, and little by little remove each quire. If the book is in an old leather binding, with a solid back, your task will be no easy one, for it is necessary to scrape away the glue from the back after it has been damped. A cloth dipped in very hot water and wrung out tightly is sometimes of use here, but you must use the greatest caution.
Having removed the leaf, or rather sheet of four pages (we will suppose that the volume has been 'cut') that requires cleaning, you have now to diagnose its complaint and prescribe the correct remedy, which you will have learnt from the text-books we have mentioned. But if the leaf is not merely stained in part, but altogether brown and discoloured, the following treatment probably will prove efficacious. Put half an ounce of permanganate of potash in a jug that holds about a pint and a half, and fill it up with hot water. Stir with a piece of wood until the permanganate is dissolved. Then lay your sheet in a developing dish and pour the hot solution in gently, taking care that there are no bubbles and that the leaf is completely covered. At the end of five minutes (or ten if the paper is thick and heavily sized) pour back the liquid into the jug, and, holding the dish over a sink, let cold water run across it in a gentle stream until all the permanganate is washed away.
The leaf will now be stained a deep brown. Stand the dish on end (the leaf of course sticks to the bottom of the dish) to drain while you prepare the bleaching part of the operation. Now take a similar jug, put half an ounce of oxalic acid into it, and again fill up with hot water. Pour this (hot but not boiling) over the leaf as before. When the leaf is as white as the dish itself, which will take from five minutes to a quarter of an hour, pour off the solution and wash the surplus fluid away. Then let the leaf wash in gently running water for one hour. Our book-hunter always uses the bath for this purpose, but a tin foot-bath under a tap does excellently. The best way to dry the leaf is to press it gently between two sheets of unused blotting-paper, then remove the upper sheet and allow the leaf to dry naturally. Remember, however, that after any washing or bleaching, leaves must always be 'sized' to give back to the paper that substance which the washing has taken out. You will find full instructions for doing this in the text-books I have mentioned. It is quite a simple matter.
Mr. Cockerell recommends that the permanganate bath be only 'warmed slightly,' and that the leaf be left in it for 'about an hour.' Our book-hunter has found (fortunately not to his cost, for the volumes which he used for experimental purposes were valueless) that this sometimes rots the paper, and on one occasion the leaves at the end of an hour came to pieces when the solution was poured off. If used hot and quickly it does not seem to injure the paper, but the water must never be so hot that you cannot bear your finger in it, and you must take care never to use a stronger solution. A strong solution of permanganate will reduce paper to pulp in a few minutes. For similar reasons our bookman prefers oxalic to sulphurous acid, but this too must never be used stronger than I have indicated. I hasten to add, however, in deference to such an excellent authority, that our book-hunter does not recommend, but merely states the methods with which he personally has been successful.
The most difficult stains to remove that the writer has yet come across are those made by a child's paint-box. Some colours are easily removed, but seventeenth-century gamboge is a perfect beast. The only successful way to deal with these 'stains' is by studying the chemistry of the 'colours,' and the re-actions of the chemicals of which they are made. With a little experimenting there is no reason why any of these pigments should not be removed successfully, and at some future period of leisure our book-hunter hopes to record his own experiences in this matter.
Here a word of warning. Do not handle permanganate of potash in the room where your bleached leaves are drying. If you do probably you will be annoyed to find small purple specks on the leaves where the fine permanganate dust has settled. It is unpleasant stuff to use, and stains everything with which it comes into contact. Undoubtedly it is at its best in a closely stoppered bottle. Rubber gloves would be useful, if they did not make one 'all thumbs.' Remember that oxalic acid will remove the stains from your hands just as well as from paper—also that it bleaches carpets. (Item, don't conduct your operations in the dining-room.) The best thing with which to handle the leaves when wet is a broad flat bone paper-knife with smooth edges. On various occasions when our bookman has not had time to complete the bleaching process, he has dried the leaves in their brown state and put them aside for a week before bleaching. So far he has not found this to have any ill effect on the paper, though possibly if kept for a longer period—especially if they got damp—the permanganate might rot them.
A very hot and strong solution of alum I have used with success for leaves that are more dirty than stained, and do not really require bleaching. Ether is excellent for stains of a greasy nature, though some may prefer the stains to the vapour which it gives off. With hydrochloric acid, so strongly recommended by some, I have never had any success. If used strong it destroys the paper, and if used weak the leaf has to be left in it for so long as to reduce the paper almost to a pulp. Remember that as a general rule, the shorter the process of washing the better. Long immersion tends to rot the fibres of the paper. With regard to staining the leaf so as to match the rest of the book, our book-hunter generally uses a solution of cigarettes (Virginians are quite the best). Possibly this is a very bad practice, but at least it is effective, the stain diffuses easily, and it can be regulated to any shade. Coffee is recommended by some.
Thumb-marks and the stains of dirty fingers are best removed by rubbing them lightly (and very carefully) with one of those disc-shaped erasers used by typists. These erasers remove the surface of the paper, so they must be used with extreme caution.[50]