In the chapter upon gall I have mentioned in a general way the action of alum water upon the edges, it remains only therefore to explain the preparation and application of the same.

To achieve beautiful results from the colors it is indispensable to wet the book edges or the paper, to be marbled, with concentrated alum water, so that no spot is left free from moisture, because at that spot the color would not take.

Concentrated alum water is prepared in the following way; put 2 quarts of water and 13 ounces of alum into a pot and heat until the alum is entirely dissolved. This concentrated solution is permitted to cool and is bottled tightly.

A solution of alum in cold water is much too weak for the above purpose as alum is but sparingly soluble in cold water.

The book edge or paper, which is to be marbled, is wet with a sponge dipped into this cold concentrated alum solution and must be allowed to dry for from 5 to 8 minutes, after which the produced edge may be lifted from the size. Generally this point finds but too little consideration in our book-binding establishments.

Edges which have not been treated with this alum water show as a consequence poor and blotted results, although such little trouble is necessary to wet the edges with alum water.

With hair-veined edges, where colors are thrown on the size only in very small quantities, this wetting may be omitted; but with comb, peacock and bouquet edges, for which four to six colors are used, it is unavoidably necessary to prepare the edges with alum water because the glycocholate aluminium formed by the color while in connection with the alum water is essential to fix the color in such quantities.

Therefore, if it is desired to produce clean and lustrous edges in which the white lines appear without a trace of color, then this advice is to be followed, the small trouble being amply repaid by the beauty of the edges.

Ordinary earth and several of the lake-colors take without wetting of edges with alum water, but these colors leave much to be desired in their divisibility and fineness and always appear rugged.

A much finer fixing medium is the acetate of aluminium which can be easily produced.

Dissolve 1 pound of alum in 3 quarts of warm water, prepare another solution with the same quantity of soda, mix these two, whereupon the hydrate of aluminium is precipitated. Allow the latter to settle, pour the water above carefully off, and filter; the white body which remains consists of hydrate of aluminium which is readily dissolved by a little acetic acid, into a clear fluid and can be diluted with the same volume of water. Then heat the whole liquid, when the excess of acetic acid is evaporated, we have the desired acetate of aluminium which can be used in the same way as alum water.

Edges and paper which are to be marbled should only be moistened with alum water or aluminium acetate shortly before the marbling and should stand not longer than a half-hour after the sizing of the edges, because later on, an insoluble layer is formed which only takes color with great difficulty. It is therefore best to prepare the colors before commencing the sizing of the edges. If there are a large number of books, it is better to divide them into two or three lots.