I’m beginning a series of posts that will introduce and describe elements of the world of Japanese paper (washi) and papermaking. I’m picking neri to describe first, because I feel that it continues to be one of the most misunderstood materials associated with Japanese papermaking. In part 1, I’d like to describe the material and explain why it is essential to the Japanese papermaking process. Part 2 will talk about what neri is NOT, and explain how it’s prepared and used.
Along with the prepared bast fibres (kozo, mitsumata, and gampi), and cold, clean water, the third essential ingredient in the Japanese papermaking process is neri. Neri is a mucilaginous liquid derived from plants (usually tororo-aoi – see part 2 for description) that is added to the papermaking vat. The addition of neri slows the drainage of the pulp solution through the screen of the papermaking tool (among other things) and allows the papermaker to more easily form sheets of even thickness.
Sometimes referred to in English as formation aid, papermakers in Japan have made use of neri since some time during the Heian period (794–1195). Washi scholars have ascertained the date for the adoption of neri by looking at the formation quality of historical paper samples — some time during the Heian period, the papers become more even in thickness, with a much cleaner formation quality. Many experts speculate that the adoption of neri came after papermakers found that making paper with gampi fibre, which has its own gooeyness, allowed them more time to manipulate the pulp solution back and forth across the surface of the papermaking screen, resulting in stronger, more even sheets of paper. It’s speculated that this discovery encouraged papermakers to seek out another source for mucilage to add to the papermaking vat for use with kozo and other fibres which have no mucilaginous qualities of their own. Whether neri is a Japanese discovery, or an innovation that entered Japan through (most likely) China or Korea, is still in debate. Historically, papermakers in different regions of Japan referred to the material by different names, including nebeshi, tamo, sana, nire, and most prominently nori (more about nori in part 2). The term neri comes from the papermaking area of Echizen and it seems that use of this word has now spread throughout Japan to the point of being nearly universal, due in part to Echizen’s prominence as a papermaking region.
Neri has a complex role in the sheet-forming process, but stated simply, neri has three unique characteristics that make it essential to the papermaking process. First, it works to slow the drainage of the pulp solution from the sugeta (papermaking tool), allowing the craftsperson time to manipulate the solution back and forth across the surface of the su (screen). Second, it encapsulates the individual pulp fibres to distribute the fibre evenly in the vat. Third, it more or less disappears when the papermaking process is complete.
DRAINAGE — The most critical function of neri is to slow the drainage of the pulp solution through the su. If a pulp solution without neri is scooped into the sugeta, the water will immediately drain through the su, leaving a clumpy mess on the surface. When neri has been added, the drainage of the pulp solution slows dramatically. In this way, the papermaker has time to deftly rock the sugeta back and forth and from side to side, evenly distributing the fibres across the surface of the su. Stated simply, by controlling the amount of neri in the vat, and thus the drainage rate on the screen, the papermaker can more easily dictate the thickness and quality of the paper.
DISPERSION — The second function of neri is to encapsulate each individual fibre, allowing the papermaker to uniformly distribute the fibre in the vat of water, and retarding the fibres’ natural tendency to sink in the vat. Scientifically speaking, the neri has a negative charge, and after encapsulating the fibre, it works to repel the fibres from each other, which prevents flocculation (clumping) of fibre. Even dispersion leads to sheets of even thickness, but it also allows for stronger and greater chemical bonds, which makes for stronger paper. Japanese papermakers talk about “koshi ga aru” (a kind of firmness) as a highly sought after characteristic, which comes at least in part from stronger and greater bonds. Other desirable traits are a compacted and less porous sheet surface, and a surface lustre — both of which are a result of increased and stronger bonds between fibres, achieved through even dispersion.
DISAPPEARANCE — The third special characteristic of neri is that, even though it has the power to slow the drainage, once the paper is formed, pressed, and dried, neri doesn’t remain in the paper, except in trace amounts. In this way, the resulting sheet of paper is essentially a mat of bonded cellulose fibres. This may seem hard to believe, but chemical analysis of finished sheets has proven it to be true. Somehow the compound breaks down, and is carried away with the water/moisture that is removed during the pressing and drying of sheets. It may be easier to understand when one considers the fact that neri made from tororo-aoi is extremely sensitive to temperature, friction, and bacteria. This is part of the reason why the best paper can be made in the winter season, when neri is most effective, and paper made in the summer, when neri is weak and quick to lose it effectiveness, is usually poor quality, limp paper. The fact that neri weakens and eventually disappears is part of what makes sheet-forming so difficult, but it is also the reason neri can safely be used in the process.