In the conservation works that were undertaken during the ninety years from 1895 to 1985, it was decided that the government would conserve the Buddhist structures in the Horyu-ji area from the point of view of the modern scientific concept of cultural properties. These conservation works were the first large-scale projects undertaken with this approach. In these projects, especially with the investigations and conservation works that involved dismantling of the buildings in the second stage of conservation work (1934-1955), specific techniques for the conservation of historic wooden structures were established. In this respect, the authenticity of a property as an historic building and as a cultural property is assured as follows:
i) Authenticity of design
Although some changes had been made in the structure and form of each building during repairs carried out before the modern age, most of these changes were only partial changes which were done either for the purpose of reinforcement or to accommodate minor design modifications, so that the design which expresses the historic value of the buildings -- the character of the plan, structure, exterior form and interior space of each building -- remains unchanged from the original.
In the conservation works carried out between 1895 and 1985, parts or materials which had been added after the time of the original construction and materials which were used later and which damaged the historic value of the buildings were removed, and missing parts and wooden members were reconstructed. However, these actions were taken only after detailed discussions by conservation committees composed of well educated and experienced specialists, taking into consideration the results of detailed investigations of the materials, techniques and traces of all kinds as well as the results of comparative studies on other historic buildings throughout Japan. The conservation works were by no means based upon conjecture.
ii) Authenticity of materials
Not only the Buddhist structures in the Horyu-ji area but also all wooden structures in Japan are constantly exposed to the risk of deterioration due to high temperatures and high humidity, as well as the risk of deterioration and damage due to fungus, insects, and wind and rain. These deteriorated materials have traditionally been replaced with new ones in order to conserve the structure of the buildings. However, since those endangered parts are concentrated mainly in the exposed perimeter areas and at the ends of buildings, such as at pillar bases, roof eave ends and around the foundations, and since most of the parts which need to be replaced are limited to these portions of the buildings, the result is the structural framework and the other fundamental parts of most buildings usually remain as original materials.
Furthermore, wooden structures in Japan are characterized by the common use of members of the same form and size, like standardized and prefabricated components. The systematic methods of modular proportioning and geometric calculation used by carpenters (Kiwari and Kiku) became highly developed. It is common for individual component types to be used repeatedly throughout the structure. Therefore, even though some parts of the buildings were missing or damaged, there remained a sufficient number of other identical parts to enable the carpenters to reproduce the missing original components. The consistent geometric calculation system also aided carpenters in their task of reproducing missing components and was especially valuable in the reconstruction of long curved roofline members and eaves.
In the conservation works of the 1895-1985 period, the condition of damage of the wooden members was closely investigated and the damaged pillars were repaired by the Netsugi (pillar bottom spliced joint) method. Hagiki (spliced fill) and Tsugiki (spliced joint) techniques were used, and efforts were made to keep the replacement of wooden members to the minimum. Those wooden members which were removed out of necessity were measured and recorded in detail, and the unusable items which were considered to have historic value were put into permanent storage.
iii) Authenticity of techniques
The authenticity of techniques is strongly related to the authenticity of materials. Traditionally the techniques of dismantling and semidismantling have been widely used in Japan because the wooden buildings in this country have wood frame structures composed of pillars and beams and employ the so-called joint construction method. This joint construction method makes it possible to dismantle, repair and reassemble buildings without damaging the original wooden members or having to abandon original construction techniques. In this sense, it may even be said that wooden structures in Japan, from the time they are first constructed, are built with later dismantlement and repair in mind.
In the conservation works carried out between 1895 and 1985, damaged materials which could not be repaired, and missing parts of the wooden members were reconstructed. The new wooden materials used were the same type as in the original, and the original construction techniques were studied so that the same techniques could be used for the conservation work. Because techniques are dependent upon the types of tools used, the conservation workers reproduced the principal tools used by the original carpenters, the yari-ganna (a kind of planning knife shaped in the form of a spear) which produces a finish that cannot be matched by contemporary tools. The greatest efforts have been made to maintain the authenticity of technique by employing such materials and tools.
iv) Authenticity of the environment
Most of the Buddhists structures in the Horyu-ji area have never been moved from their original locations, and most are well conserved together with the characteristic features of their surrounding environments. The composition of these buildings is also considered to have important historical meaning, and care has always been taken to conserve it.
It is a fact that wooden structures, if left untouched, are easily damaged. However, with appropriate management and conservation, it is possible to conserve them with little need for large-scale change. The permission of the government based upon detailed examination by the Council for the Protection of Cultural Properties -- composed mainly of specialists and including many members of Japan ICOMOS -- is needed for any change in the existing state that may entail the removal or reproduction of parts or materials in the process of the restoration of historic structures in Japan, including that of the Buddhist structures in the Horyu-ji area.
