Double-leaved books originated in China and were also used in regions influenced by the Chinese, such as North Vietnam and Singapore. The technique was also commonly used in Japan even into the modern machine printing era. The soft, lightly sized paper used for these structures tends to be quite porous and translucent, thus inks tend to migrate through the paper and text and graphics are applied only to one side of the sheet. The sheet is then folded in the middle with the plain surfaces together to make an apparent leaf with the text on both sides.
Wood block printing was the most common method of rendering both texts and graphics. The group of folded leaves was then assembled and stitched at the back through the unfolded edge. A simple paper (and sometimes paperboard) cover was attached at the front and back of the book and the text block fastened together by means of paper twists pushed through holes piercing the entire text block at the back and by thread stitches. The light structure and small size of these books tends to reduce the incidence of binding structure damage to broken thread and abraded covers. However, in many cases there is considerable insect damage to the leaves, no doubt because of the rice starch used to size the paper, and repair treatment is complicated by the need to retain the paper's soft and pliable nature. If the insect damage is extensive, the book must be disbound in order to carry out the repairs.
If the conservator is not familiar with the language of the text, the leaves should be consecutively numbered in an inconspicuous place with a soft pencil to ensure that the book can be collated accurately after treatment. The sewing pattern should also be documented so that it can be reproduced.
Repairing insect damage
Each of the insect holes may be repaired with thin tissue patches or a pulp made from paste and macerated tissue. Even though the back of the text is blank, the leaf should not be simply wet laminated, as this stiffens the leaves. The small patches are applied with starch paste from the back of the leaf, which should be placed face down on a polyester film surface, preferably on a light table. Repairing the insect holes in this way is extremely time consuming, and if there are a large number of insect damaged books, the leaf caster is the best way to perform the repairs. When repairs are dry, the book should be reassembled with new twisted paper slips and the replicated sewing pattern.
Over the years, damage to individual double-leaved books or for small groups of books was minimized by light-protective enclosures. Replicating these enclosures is quite simple, although if new cases are needed, some consideration might be given to the use of MM cases.
