Happy Materials Monday! Today we are going to talk about the history, processing and use of Japanese tissue in paper conservation.
One of the most common materials found in book and paper conservation is Japanese tissue or Washi; from Wa- meaning Japanese and shi- paper.
What is it?
Japanese tissue is a traditional paper made up of plant fibers. It can be made of the following plants; Broussonetia papyrifera, Diplomorpha sikokiana, Edgeworthia chrysantha or kozo, gampi or Mitsumata. Kozo tissue is the most widley used and will be the focus of our post today. The Mulberry tree from which kozo tissue is made is found all throughout Asia; in China, Cambodia, Japan, India and Laos. The tree is small and quick growing which allows for large sustainable harvests in short periods of time.
The tissue made from these trees are particularly useful in conservation because unlike western papers there is no grain direction that creates "pull". The fibers of the paper crisscross while maintaining tissue paper thinness and can even exceed the strength of western papers. Thus allowing the conservator to not only create a strong mend but also blend the new material in with the old, creating a seamless transition.
Washi has been made in Japan for over a thousand years. It was first introduced in the 7th century by the Chinese and since then the Japanese have excelled at it. Washi has become an important part of Japanese culture. The Japanese have and continue to use washi in the making of traditional crafts; bowls, utensils, wood block prints, lamps, screens and in wedding rituals. Traditional washi making has been added to UNESCO's representative List of the Intangible Cultural Heritage of Humanity.
How is it made?
The tissue is made up of the mulberry tree's inner bark. The processing steps are harvesting, steaming, bark extraction, boiling, separating barks, drying, bleaching, removal of impurities (by hand) and then finally the floating of the fibers in water to create the paper sheets. At that point we move to drying once again. This short video lays everything it wonderfully.
As you can see the process is time consuming, however, the quality that is achieved is unmatched. This level of quality is important to conservation because we are focused on the long term preservation of cultural heritage items. If the tissue had impurities in it or was weaker in one part that would affect our quality of work and ultimately the object itself.
How do we use it?
When mending paper, a conservator at first looks at the weight, texture and color of the paper they are working with. This information will inform what type of tissue will be used in the mend. Let us take a book page as an example. If the tear runs through the words then an extremely thin piece of tissue (Berlin tissue) would be the likely choice. The tissue is chosen, torn with either a sharp instrument or water torn (watercolor pen) and then applied with wheat starch paste. For particularly tricky mends where there is media on both sides of a paper; long fibers can be removed from a tissue, dipped in wheat starch paste and used almost like stitches across the tear.
For the librarian or collections care worker there is a quicker variety that is called heat set tissue. This tissue has a special adhesive applied to it and is sold in rolls. A heated spatula is used to warm the adhesive and with the added pressure the mend is complete. This type is chosen for either speed or because support material (paper) cannot stand added moisture from the wheat starch paste.
This material is so ubiquitous to conservation that it spans many different disciplines throughout the field. Objects conservators use it in repairing mummy wraps, violins and ceramics. Paintings conservators use it to temporarily consolidate paint while working. Paper and book conservators use it to mend paper of course and can also be used to recreate leather or cloth losses on a binding. We frequently line the spine of a book as a protection layer between different added adhesives and layers of cloth or paper. We use it for so many different applications that I cannot imagine one other material that is more important to our work.
1. Royal Botanic Gardens at Kew, http://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:850861-1#source-KSP
3. Pauline Webber, 'The use of Asian paper conservation techniques in Western collections' in Adapt & Evolve 2015: East Asian Materials and Techniques in Western Conservation. Proceedings from the International Conference of the Icon Book & Paper Group, London 8-10 April 2015 (London, The Institute of Conservation: 2017), 12-27 https://icon.org.uk/system/files/public/Publications/AandE15/2-ae15_webber-12-27.pdf
1. Take a look at a conservation materials supplier for a broad ranch of tissues that can be used in our work; https://www.talasonline.com/paper-and-board/japanese-korean/sheets