Online Lecture 6
文化財彫刻の修理に使用する充填剤および古色について
1.Introduction

When new parts are added to a statue during a restoration, 'color matching' is carried out in order that they may blend in with the rest of the work.  In the past, before the concept of 'cultural properties' became established, the ideal was for skilled craftsmen to color new repairs to make them indistinguishable from the rest of the work. However, this method invites unnecessary confusion in the study of art history and so today the accepted method is for new sections to be colored in such a way as to make them obvious.

Recently the importance of these cultural properties as subjects of religious devotion has been reconsidered, leading to an increased understanding in the restoration field of the necessity to color new parts to blend in with the old more naturally. In order to meet the demands of the times, we have undertaken various experiments to discover improved methods of coloring as well as testing various resin fillers, which have become an indispensable material for the restorer.

We produced various samples of 'aged' coloring and resins during our restoration of Joruri-ji temple's 'Seated Statue of Dainichi Nyorai' (Vairocana) and Korin-ji temple's 'Soshi-zo' (Founder’s Statue). When undertaking a restoration, the selection of materials is often decided by the restorer's level of proficiency. For students or comparatively inexperienced restorers, the choice is huge and despite reference to reports or the advice of experienced restorers, it is a comparatively difficult decision to make. We hope that the samples we made during the present restorations will prove useful as a basis for objective selection in the future.

2.
Test Procedure

Joruri-ji temple's 'Seated Statue of Dainichi Nyorai' and Korin-ji temple's 'Soshi-zo' statue, which our laboratory has been working on since 2005, required some replacement parts and filling. As it had been decided that these works were to be given a natural wood finish, the new parts were colored to match the original timbers. We also produced test samples of the resin fillers, used to fill wormholes, etc., in order to provide reference material for future restorations.

2.1
Wood Aging Using Dyes

Wood can be aged by physically degrading it through an application of nitric acid or exposing it to gamma rays, but we decided to create samples of aging achieved through dying. Each sample consisted of a 3cm by 3cm piece of Japanese cypress wood that was planed then dyed using: 1) Yashadama (obtained by boiling dried alder fruit or bark to create a brown dye), 2) Kakishibu (obtained by soaking fermented persimmon fruit in distilled spirit to produce a waterproof brown dye), 3) Acene, 4) Green tea/ammonia solution. Ten gradations of each color were created and compared, the solutions of each dye being listed below.
 (1) Yashadama: 100g of dried alder fruit were placed inside 1 liter of water and boiled until 500cc remained.
 (2) Kakishibu: Used undiluted
 (3) Acene: 1g of acene was mixed with 100cc of water and heated until it dissolved.
 (4) Green tea/ammonia: 3g of tea leaves was mixed with 300cc of water and allowed to simmer for 5 minutes, then 2 to 3 drops of ammonia added. 

2.2 Resin Filler

For the resin filler tests we used two popular resins, Primal AC (a water-based acrylic resin) and PVA-Jade (a polyvinyl alcohol-based resin) to which we added five types of extender: sawdust, tabu powder (powdered leaves of the Machilus thunbergii tree which become adhesive if mixed with water), tonoko (powdered burnt clay or pulverized whetstone), acrylic microballoons, and phenolic microballoons, then checked for adhesion, and shrinkage ratio.
(1) Primal AC + Sawdust: Adhesion to the wood is strong, but there is high shrinkage resulting in cracks in the center.
(2) Primal AC + Microballoons: This has the lowest shrinkage factor and compatibility with the wood is good but it is slightly soft.
(3) Primal AC + Tabu Powder: The shrinkage factor is quite low and it is suitably strong, but adhesion to the wood is poor.
(4) Jade + Sawdust: Adhesion to the wood is strong, and the shrinkage factor is quite low but it does not detach from the spatula easily.
(5) Jade + Tabu powder: Adhesion to the wood is strong but the shrinkage factor is quite high and it does not detach from the spatula easily.

The quantity of resin was the same in each test, but as the relative density of the different filler additives varied, so too did the quantities used. Each was mixed to produce the consistency most suitable to work with.

Numerous parameters may be proposed to describe the ideal filler: shrinkage, its compatibility with wood, color, malleability, etc., and overall, we found that the fillers with microballoons added were the best. Their stiffness was a problem, but we were able to overcome this through the addition of tabu powder.  It proved easier to mix colors using acrylic microballoons than phenolic microballoons. Filler with PVA resin as the main ingredient would not detach from the spatula easily.
2.3 ’Aged’ Coloring Using Lacquer

There are numerous ways of achieving 'aged' coloring using lacquer: adjusting the tone through the addition of pigment or powdered sumi ink, using a lot of transparent lacquer, etc., but we limited ourselves to the following five techniques for our experiments.
(1)Sabitataki Coloring 
After sizing the wood (by allowing raw lacquer to soak into it), sabi-urushi (a primer comprising of lacquer and tonoko [burnt clay] that has been mixed to a paste with water) is applied than patted repeatedly with a pad consisting of cotton wool wrapped in cloth to create a textured surface (a technique known as sabitataki). An undercoat of gofun (a whitewash made from seashells) is applied and then the coloring carried out. After the coloring has dried, the surface is lightly rubbed down using sandpaper, etc. The gofun had a small quantity of black sumi ink added, while the pigments used for the coloring were oxidized by burning, etc.
(2)Weak Sabi Coloring
After sizing the wood, a coat of sabi-urushi with a low ratio of lacquer, is applied. An undercoat of gofun is then applied and the coloring carried out. After the coloring has dried, a knife or file is used to scrape down the surface, while checking the results visually. The gofun had a small quantity of black sumi ink added, while the pigments used for the coloring were burnt, etc., in order to make them oxidize.
(3)Applied Cracks
Prepare the wood by sizing. Paste washi paper to another piece of wood, the same shape as that which is being colored, then apply sabiurushi and shippaku (gold leaf over lacquer).Use hot or cold water to remove the lacquered paper intact from the wood, then create cracks in the surface using the hands or a spatula.Paste washi paper to the front surface of the lacquer in order to protect it. Remove the paper from the rear of the sabiurushi and pressure-bond it to the work.
(4)Shippaku (Gold Leaf over Lacquer)
Size the wood that has been carved to create the statue's garment, apply the sabiurushi and then the shippaku (gold leaf over lacquer) in the normal way. Before the lacquer base for the gold leaf has completely dried, rub it lightly with a cloth, etc., to remove the gold while checking the results visually. When the lacquer has completely dried, use light colored acrylic paint to tone down the gold and before this has dried, sprinkle the surface with susudama (lampblack), etc.
(5)Woodworm Technique
Size the wood then use a narrow icing funnel or something similar to apply a paste consisting of glue and tonoko to create the lines that will become the wormholes. Coat the thin cord of tonoko with sabiurushi to strengthen it. Rub down the surface to achieve a flat finish then apply the lacquer.When this has hardened, use warm water to wash away the tonoko.
3 Summary

In the case of Joruri-ji temple’s seated statue of Dainichi Nyorai, we compared the color of the original wood to a color chart and chose Yashadama for the 'aged' coloring.For the filler to be used on Korin-ji temple's Soshi-zo, we chose to use Primal AC with acrylic microballoons as this displayed the least shrinkage. However, in order to improve its texture and malleability, we added tabu powder and sawdust, the final ratio being: Primal AC - 2, acrylic microballoons - 4, tabu - 1, sawdust - 1. In applying 'aged coloring' using lacquer, we experimented using the applied cracks' technique on the new wood on the back of the right hand of Joruri-ji temple's Dainichi Nyorai.