Japanese tissue is a thin, strong paper made from vegetable fibers. Japanese tissue may be made from one of three plants, the kozo plant (Paper Mulberry tree), the mitsumata shrub and the gampi tree. The long, strong fibers of the kozo plant produce very strong, dimensionally stable papers, and are the most commonly used fibers in the making of Japanese paper (washi). Tissue made from kozo, or kozogami (楮紙), comes in varying thicknesses and colors, and is an ideal paper to use in the mending of books. The majority of mending tissues are made from kozo fibers, though mitsumata and gampi papers also are used.
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The kozo plant is used in the manufacture of the following papers:
| Paper | Composition | Description and use |
|---|---|---|
| Goyu | 90% kozo | This paper is used mainly for printing and for the hinges of mounting paper materials. |
| Hosokawa ohban | 100% kozo | This is heavier than other Japanese papers and is used as a backing for documents and maps. |
| Kaji | 100% kozo | This lightweight paper is used for conservation processes. |
| Kizukushi | 100% kozo | This paper is used for mending. |
| Misu | 100% kozo | This paper is used in conservation processes. |
| Okawara | 100% kozo | This paper is also used in conservation. |
| Sekishu | 80% kozo | This paper is used for printing and in conservation. |
| Sekishu kozogami mare | 100% kozo | Used in mending. |
| Sekishu kozogami turu | 100% kozo | Used for all types of mending. |
| Udagami | 100% kozo | This opaque paper is used for mending artworks on paper. |
The gampi plant is used in the manufacture of the following papers:
| Paper | Composition | Description and use |
|---|---|---|
| Sekishu Torinoko Gampi | 100% gampi | This soft, silky paper looks as if it is glazed and is used for mending and conservation of artworks on paper. |
The mitsumata plant is used in the manufacture of the following papers:
| Paper | Composition | Description and use |
|---|---|---|
| Kitakata | Mitsumata and sulfite pulp | This silky paper is buff in color and is used for mending older books and documents. |
Japanese tissue paper is a hand-made paper. The inner bark of the kozo plant is harvested in the fall and spring, with material from the fall harvest being considered better quality. Bundles of kozo sticks are steamed in a cauldron, then stripped of their bark and hung in the sun to dry. At this stage in the process, it is known as kuro-kawa, or black bark.
To make paper, the black bark must be converted into white bark. The stored black bark is soaked and then scraped by hand with a knife to remove the black outer coat. It is then washed in water and again placed in the sun to dry.
White bark is boiled with lye for about an hour, then left to steam for several more hours. At this point, it is rinsed with clear water to remove the lye. Then, it is stream bleached (kawa-zarashi). The fibers are placed in a stream bed around which a dam is built. Clean water is let in periodically to wash the fibers. Alternatively, the fibers may be bleached using a process called small bleaching (ko-arai). In this case, it is first placed on boards and beaten with rods before being placed in a cloth bag and rinsed in clear running water.
Impurities are removed after bleaching though a process known as chiri-tori. Any remaining pieces of bark, hard fibers or other impurities are picked out by hand or, in the case of very small pieces, by the use of pins. The remaining material is rolled into little balls and the balls are then beaten to crush the fibers.
After being beaten, it is common for the kozo fibers to be mixed with neri, which is a mucilaginous material made from the roots of the tororo plant. The neri makes the fibers float uniformly on water and also helps to "...slow the speed of drainage so that a better-formed sheet of paper will result." (Narita, p.45)
A solution of 30 percent pulp and 70 percent water is then mixed together in a vat. Neri may also be added to the vat. Nagashi-zuki, the most common technique for making sheets of paper, is then employed. The mixture is scooped on a screen and allowed to flow back and forth across the screen to interlock the fibers. This process is ideal for forming thin sheets of paper. The other technique for making paper, tame-zuki, does not use neri and forms thicker sheets of paper.
The sheet of paper is placed on a wooden board and dried overnight, then pressed the next day to remove water. After pressing, the sheets are put on a drying board and brushed to smooth them. They are dried in the sun, then removed from the drying board and trimmed.
Japanese tissue is used in the conservation of books and manuscripts. The tissue comes in varying thicknesses and colors, and is used for a variety of mending tasks, including repairing tears, mending book hinges, and reinforcing the folds of signatures (the groups of pages gathered and folded together at the spine) or for reinforcement of an entire sheet through backing. The mender will select a piece of Japanese tissue that closely matches the color of the paper being mended, and chooses a thickness (weight) suitable to the job at hand.
First, Japanese tissue in a color close to that of the paper to be mended is chosen. The tear is aligned and paste may be used on any overlapping surfaces in the tear to help hold it together during the mending process.
A strip of tissue is torn away from the main sheet using a water tear. This is done by wetting the paper along the area to be torn and then pulling sideways with the fingers to separate the strip from the rest of the sheet of tissue, so that it will have feathered edges. The fibers in these feathered edges will allow the tissue to have a firmer hold on the mended paper and also to blend in with it once dried.
Paste is applied to one side of the tissue strip, from the center outward. The tissue is then placed, paste side down, on the tear, leaving a little bit of the mending tissue hanging over the edge. This bit will be trimmed off after the mend dries. A dry brush is used to smooth the tissue over the tear, again, from the center outward. The mended page is placed between layers of PET film or glass board, blotting paper, and reemay (to keep the paste from sticking to the blotting paper), then weighted and left to dry.
This is another task in which Japanese tissue is often used. In some cases, the first step may be to tip in (that is, add with a thin strip of adhesive) a flyleaf to become the base for the attachment of the hinge mend, if the original flyleaf is not well attached. A small support the height of the spine should be placed to eliminate stress on the hinge.
Japanese tissue should be water torn in the same process as described above, in a width and length sufficient to cover the hinge of the book with about 3/8 inch extension over the sides. Paste should be brushed on to the tissue, from the center outward, transferred to the hinge and then brushed down with a dry brush.
A sheet of PET film is placed to prevent the hinge from sticking together and it is weighted until it dries.
In the case where an entire signature (a folded sheet of paper forming several pages, or leaves, of a book) has come out, it may be reinserted by being sewn first onto a strip of Japanese paper, and then by pasting into the book along the newly-formed hinge between the Japanese paper and original signature.
The E. Lingle Craig Preservation Laboratory Repair and Enclosure Treatment Manual