写真ガラス原板の保存修理と活用

文化財の概要

重要文化財 法隆寺金堂壁画写真ガラス原板 363枚

ガラス乾板(コロタイプ原板)

縦55.6~61.0cm 横44.6~46.0cm

昭和10年(1935)撮影

奈良 法隆寺蔵

 英国イルフォード社製のガラス乾板を使用。撮影の翌年にコロタイプ印刷用の版を作成するため膜面を剝がして反転させ、大半を別の厚手のガラス板に貼り替えている。

保存修理事業

 平成27年(2015)、法隆寺が所有する写真ガラス原板は、便利堂が所有する法隆寺金堂壁画写真原板(同じときに撮影された四色分解写真、赤外線写真など83枚)とともに国の重要文化財に指定された(歴史資料部門)。指定後の平成28年(2016)から5年をかけて修理事業が実施されている。この事業では、保存に万全を期するためにクリーニングと保存箱の製作がおこなわれ(国庫補助。令和元年度まで)、さらに写真ガラス原板が保持する極めて高い記録性と再現性を活用すべく、高精細デジタルスキャナーをもちいたデジタル化が進められている(国庫補助、朝日新聞文化財団助成。令和元年度から翌年度まで)。ここに紹介するのは、取り込みと接合作業が完了した画像である。

 デジタル化にあたっては、全紙判という類例の少ない大きさにあわせて1,500dpiの解像度で画像を取得できる専用の大型スキャナーが開発された。このスキャナーを使用して写真ガラス原板1枚を5本の帯状に分割して取り込んだ後、1枚の画像に接合し、さらに撮影時のレンズの歪みや現像時に生じた濃淡の差などを補正しつつ、複数の画像を1面の壁画の大きさに再接合している。完成した壁画1枚の画像は、大壁で300億画素、小壁で170億画素を超える巨大なサイズとなっている。再接合作業には、文化財活用センターの協力が得られた。

デジタル画像の活用

 法隆寺の収蔵庫に保管されている焼損壁画(旧壁画)について、調査と将来的な公開を見据えた検討が進められているなか、写真ガラス原板の活用や、研究資料としての利用にも高い関心が寄せられている。令和元年度より、法隆寺と奈良国立博物館、国立情報学研究所高野研究室は、スキャニング画像と再接合された巨大な画像の保存活用を目的として共同研究を実施している。このたび公開するコンテンツは、その成果のひとつである。この精緻な画像の公開が、法隆寺金堂壁画の比類なき価値を社会に伝え、文化財保護に対する理解を深める一助となることを願う。

法隆寺金堂壁画について、より詳しく知りたい方へ

法隆寺監修、朝日新聞社編『法隆寺金堂壁画』朝日新聞社、1994年11月

法隆寺監修、朝日新聞社編『法隆寺再現壁画』朝日新聞社、1995年10月

「法隆寺金堂壁画」刊行会編『法隆寺金堂壁画 ガラス乾板から甦った白鳳の美』岩波書店、2011年6月

奈良国立博物館編『重要文化財 法隆寺金堂壁画写真ガラス原板―文化財写真の軌跡―』奈良国立博物館、2019年12月

東京国立博物館ほか編『法隆寺金堂壁画と百済観音』朝日新聞社・NHK・NHKプロモーション、2020年3月

デジタルビューアを見るGlass Photographic Plates of the Murals in the Kondō Hall of Hōryūji Temple ―Digital Viewer―

The Conservation and Utilization of the Glass Photographic Plates of the
Kondō Hall Murals at Hōryūji Temple

About the Glass Photographic Plates

Important Cultural Property

The Glass Photographic Plates of the Kondō Hall Murals at Hōryūji Temple

Taken in 1935 (Shōwa 10)

363 plates for collotype printing

H. 55.6 to 61.0 cm, W. 44.6 to 46.0 cm

Hōryūji Temple, Nara

The photographs were taken using glass plates from the British company Ilford Photo; the following year, in order to create reproductions using collotype printing, their film surfaces were peeled off and reversed—inverting the mirror images of the photographic negatives—and parts were affixed to another thick glass plate.

The Conservation Project

In 2015, the glass photographic plates owned by Hōryūji Temple and the photography of the Kondō Hall murals owned by Benridō (83 normal and four-color glass plates, infrared photography, and others, all taken at the same time as those owned by Hōryūji Temple) were together designated Important Cultural Properties of Japan in the category of historical materials. Conservation work on the glass plates began in FY 2016, the year after their designation as Important Cultural Properties, and it lasted five years. The project was made possible by a national subsidy for the conservation of cultural properties and by a grant from the Asahi Shimbun Foundation. The undertaking began with the scrupulous conservation of the plates in anticipation of storing them: they were cleaned and protective boxes in which they could be safely preserved were custom made. (This part of the project was completed in FY 2019.) Furthermore, in order to fully utilize the glass photographic plates’ great capacities at recording visual information and their reproducibility, a high definition digital scanner is currently being used to digitize them. (This part of the project began in FY 2019 and will continue through next year.) The images that are presented here are those that have already been captured and synthesized through this process.

The digitization has proceeded using a dedicated large-scale scanner that can scan 1,500 dpi (dots per inch); it can scan materials even larger than the glass photographic plates to create a high resolution digital image. The scanner divides each glass photographic plate into five sections, scanning each section separately. It then combines what it has scanned into one image. After this, the images are edited. Any distortions caused by the lens or inconsistencies of light or shade at the time of shooting are adjusted and corrected. Following this, the digitized glass plates are combined with the others to form a reproduction of the mural in full and true to scale. By the time the glass photographic plates have been digitized and combined to reproduce an entire mural, the resulting images are immense. Those of the large bays are over thirty giga-pixels, and images reproducing the murals on the smaller bays are over seventeen giga-pixels. The work of synthesizing the digitized glass plates into these true-to-scale reproductions of the murals was undertaken with the cooperation of the National Center for the Promotion of Cultural Properties.

Applications of the Digital Images

As many eagerly anticipate studies and future exhibitions involving the damaged murals now in storage at Hōryūji, the glass photographic plates are also garnering great interest as research sources and as cultural assets with great potential for utilization. Starting in FY 2019, a collaborative project between Hōryūji, Nara National Museum, and the research office of Takano Akihiko at the National Institute of Infomatics was undertaken with the goal of scanning the images of the glass photographic plates and creating massive composite reproductions of the murals, efforts that serve the broader project of conserving and promoting cultural properties.

The digital resources presented here are the product of one component of this project. We hope that by making these images and their every detail more accessible, not only will the unmatched importance of the Kondō Hall murals of Hōryūji be conveyed to a wider audience, but so, too, will a heightened understanding of the importance of conserving cultural properties.

デジタルビューアを見るGlass Photographic Plates of the Murals in the Kondō Hall of Hōryūji Temple ―Digital Viewer―