Fig. 27b.
Some knowledge of their respective disadvantage should be acquired, however, in order to avoid, or at least minimise, them.
Take, for instance, a course of eight printings, each one absolutely necessary to the design, and each one to be dried by stoving. It is only reasonable to suppose that the first and second printings will be seriously affected by the subsequent stovings. They will undoubtedly harden to such an extent as to render the super-position of other colours a difficult matter, and their purity of tone will most probably be affected. According to the same line of reasoning, some sheets would be more affected by the heat than others, owing to their position in the racks, the heat of stoves being greatest near the top.
Air-drying can only be accomplished by adding to the printing ink a proportion of some suitable drier. (See Transfer Printing, [p. 71].) Naturally, it requires a much longer time, but it is equally effective, much less troublesome, and generally more satisfactory.
Fig. 28.—Convenient method of stacking decorated metal plates to distribute their weights and prevent injury.