CHANGES IN CELL STRUCTURE OF DRY ARCHAEOLOGICAL WOODEN PLATES, TRIPITAKA KOREANA
Sang Jin Park, Ae Kyung Kang, So Yun Park
Dept. of Wood Science & Technology, College of Agriculture,
Kyungpook University, Taegu, Korea.
SUMMARY
Tripitaka Koreana engraved the Buddhist scriptures on 81,340 wooden plates made during the Coryo Dynasty from 1236 to 1251 A.D. Some plates were varnished with Rhus lacquer, however, most were uncoated. The microscopic structure of plates appeared intact due to storage in a well ventilated wooden-house. However, wooden plates were irregularly used for copying the works with ink. Hence it can be expected that they were exposed repeatedly to ink-water and drying processes. The following work was undertaken to examine the changes in cell structures which occurred during the long-term ageing process in these dry archaeological wooden plates, using light, scanning and transmission electron microscopy. The wood samples were taken from the edges of wooden plates and wood species examined were Prunus sp., Pyrus sp., Daponiphyllum macropodum, Betula schmiditii and Machilus sp.
One of the characteristic features of these wood samples was the occurrence of cracks in the fibres and delamination of the secondary wall from the middle lamella not only at the surface (apparently degraded) but also in the internal part of wood samples which appeared sound. Microscopic examination showed these cracks as helical fissures in longitudinal sections. Helical fissure originated mostly from the expansion of pits parallel to the microfibrils and were present mainly in the radial sections. Cracks and helical fissures were found only in the Tripitaka wooden plates but not in recent wood samples which were dried rapidly at high temperature for evidence of deterioration.
A large amount of hyphae in vessels and the degradation of vessel-ray pit membranes by the fungal hyphae were observed in the wood samples examined However, vessel walls were intact and axial parenchyma cells were also well preserved even though adjacent fibre walls were severely deteriorated. Interestingly helical fissures in the fibre cells just beneath the lacquer layer were seldom observed. Some hyphae were also present in the vessels impregnated with Rhus lacquer. The extent of degradation varied depending upon wood species: Prunus sp. was the most deteriorated and the degree of deterioration in decreasing order was Pyrus sp. B. schmiditii and D. mcmpodum.
Keywords: Archaeological wood, Tripitaka Koreans, Bhuddist, degradation, cell walls, Prunus sp., Pyrus sp., Daponiphyllum sp., Betala sp., Machilus sp.
INTRODUCTION
Tripitaka Koreana were made during the Coryo dynasty from 1236 to 1251 AD. Buddhist scriptures were engraved on 81,340 wooden plates. Each plate was about 70 cm long, 24 cm wide, 2-3 cm thick and 3-3.5 kg in weight. About 700 letters were carved in both sides of the plates. Most of these plates were uncoated except for some which were varnished with Rhus lacquer. Macroscopically, Tripitaka plates appeared intact due to storage in a well ventilated wooden house. However, they must have been exposed repeatedly to ink solution and to the drying process during the irregular copying of the works. The following studies were undertaken to examine changes in cell structure which occurred during long-term aging processes in these dry archaeological wooden plates using light, scanning and transmission electron microscopes.
MATERIALS AND METHODS
Wood samples were taken from the edges of the plates. Wood species examined were Prunus sp., Pyrus sp., D. mcmpodum, B. schmidiiii and Machilus sp. For microscopic examinations, wood blocks of Prunus sp. were treated with standard procedures described elsewhere.
RESULTS AND DISCUSSION
Wedge-shaped cracks were found from the lumen side toward the compound middle lamella (Fig.1). Also delaminations of the secondary wall from the compound middle lamella were often observed (Fig.2). Cracks were found not only in the surface (apparently degraded) but also in the internal part of the wood samples, which appeared sound. These cracks as helical fissures were present mainly in radial sections and originated mostly from the expansion of pits (Fig. 3). Cracks appeared first as hairline checks and seemed to be enlarged slowly, running parallel to the microfibrils. In contrast, they were rarely observed in the tangential cell walls. These helical fissures were not observed in recent wood samples, indicating evidence of deterioration of the dry archaeological Tripitaka plates. When compared to recent wood, the birefringence of wood fibres was considerably lower or completely absent, suggesting the degradation of crystalline cellulose in these wood samples. In contrast, vessels retained their birefringence (Fig. 4). The thinning of the wood cell wall and/or typical fungal cavities in the S2 layer were not observed in the present wood samples.
A large amount of hyphae in vessels and the degradation of vessel-ray pit membranes by the fungal hyphae were observed (Fig. 5). However, the vessel wall remained intact and axial parenchyma cells were also well preserved despite the serious helical fissures which occurred in adjacent fibre walls (Fig. 6). Neither helical fissures nor hyphae were present in ray parenchyma. However irregular dentate cracks were observed in some radial walls (Fig. 7). Interestingly, helical fissures were seldom observed in the fibre cells just beneath the lacquer layer. Some hyphae were also present in the vessels impregnated with Rhus lacquer.
CONCLUSIONS
Our work has shown that considerable structural changes have taken place in the wooden plates during storage, despite their intact appearance. Since ink solution was deposited during the copying of these wooden plates, they may have retained a high moisture content for intermittent periods. Thus it can be assumed that some fungi had colonized the wood cell wall during these periods. Preservative measures are urgently needed for the protection of these wooden plates from fungal degadation.