If very dry the non-cohesive clay will turn to a white powder. Moreover, this clay-laden paper will not hold binding threads, so again it has to be preserved. A book printed on such material has to be treated in the same way as I have described in the case of wood pulp paper.
There is, however, a plan of preserving prints on clay, and this is to fasten down the printed portion on a piece of sound paper from the beginning. This is already done to some extent, and it should be universal in the case of isolated plates, but when a book is all printed on clay paper, as many fine and valuable books unfortunately are, it is difficult to say what is best to be done. The only real remedy seems to be a refusal on the part of purchasers to buy such books. But purchasers do not always know when they are buying clay instead of paper. It is, however, not difficult to tell, as the clay-laden paper feels very smooth and soft to the touch of a dry finger. This peculiarity can be easily detected in one or other of the American magazines, Harper’s or Scribner’s, and the difference between the feel of a page holding an impression from a fine half-tone block, and that having only text, will at once be evident.
If a mark may be made on a suspected sheet, a drop of water should be put upon one corner, left a second or two, and then dried off with blotting-paper. Now a light scrape with a knife over the damped place will remove a layer of white clay if it is there.
There is no doubt that the large majority of our modern books will not be in readable condition in about a hundred years’ time from the date of their publishing.
BOOKS TO CONSULT.
Paper.
Arts, Society of.—Report on the Deterioration of Paper. London, 1898.
Blades, W.—(Athenæum, March 30th, 1889, p. 409. Paper on Watermarks).
Blanchet, A.—Essai sur l’histoire des Papier. Paris, 1890.