Fumigation at the basement of Toyokan
Kanba : Here is the basement of Toyokan. The basement of Toyokan was originally an exhibition space, but it has been used as a temporary storehouse after Heiseikan opened. All exhibition rooms of Toyokan closed in June 2009, and earthquake-proofing work of Tokyokan will be carried out until 2011. Therefore, we are transferring all collected items from Tokyokan to other places. In order to prevent insects and mold from moving to and polluting other places when transferring items, especially when transferring large amounts of them, the items are fumigated and then transferred to other places. This is Mr. Araki, who is on the staff of the conservation division and in charge of preservation and conservation of the environment.
Araki : In this place, items that were stored in Tokyokan have been fumigated. This is a tent used for fumigation. This time, we use carbon dioxide to perform gas fumigation. Items are in turn placed in the tent, and the films of the tent are bonded by thermal compression to totally enclose the tent. The air inside the tent is removed through the upper part of the tent while injecting carbon dioxide into the tent. By doing so, carbon dioxide penetrates inside the items, so insects and their eggs can be killed. Approxi-mately 60 to 70 % concentration of carbon dioxide is maintained in tent for about two weeks. Fumigation using carbon dioxide has been generally performed in recent years. Until then, fumigation using highly toxic chemical agents, including methyl bromide and ethylene oxide, had been widely performed. However, the Montreal Protocol stipulated that methyl bromide depletes ozone, and it was totally abolished in advanced countries. Therefore, methyl bromide cannot be used as a fumigant. Then, carbon dioxide fumigation began to be performed as an alternative and as an environmentally-friendly method. Ideally, fumigation using chemical agents should be avoided as much as possible, and another method should be used to reduce insects and mold. In order to do so, we should pay attention to frequent inspections, cleaning and treatment on a day-to-day basis. However, at this time, we are transferring large amounts of items, and there is a possibility that insects creep into the items, so fumigation has been performed.
Q : What kind of insects are there?
Kanba : Wood cellulose and protein in wool attract many insects. Wool is infested with an insect called "clothes moth." There are many types of insects. In a recent case, an outbreak of "silverfish," an insect eating paper, occurred in this museum. That insect is very harmful, so we have been systematically reducing the number of the insects by performing cleaning, fumigation and inspections. (continued in the upper right column)
Tokyokan
Items being fumigated
X-ray radiation place
Araki : Here is the basement of the museum, and this place is an X-ray radiation place, commonly called "radiation place," at which cultural properties are investigated by using X-ray. This computer acts as a controller of an instrument which generates X-ray, and synthesizes and saves data. Also, the computer can process images taken by the X-ray instrument. The instrument that generates X-ray is called "X-ray tube." The flat panel detector that is exposed to X-ray is placed under the tube. Films used to be placed here, but, in the present, images are digitally processed as a result of the arrival of digitization. Cultural properties are laid between the tube and the detector. When X-ray is applied, the X-ray passes through cultural properties and reaches the panel. Since the strength of the X-ray changes according to the thickness and material of the cultural properties, darker parts and paler parts are formed on the panel. We are planning to investigate archaeological iron swords and artifacts after two to three weeks. Metal artifacts are covered by rust. As for a sword, we are going to investigate to what extent a shape of the sword remains inside rust. An inlay, gold inlay or silver inlay might be left inside. Those items can be seen by using X-ray. Also, if it is a set of characters, it is a major discovery. The past major discoveries include the "Ohshimei" iron sword, "Todaiji-yama" gold inlay sword, and "Etafuna-yama" sword, which were made in the Kofun Period. Those items were discovered by using X-ray. It is not certain that such items can be found in this investigation, but it might be possible to find such items as a result of this investigation. We also take an X-ray of items such as paintings. An X-ray of a long item can be taken by moving the instrument across the surface. (continued in the lower column)
X-ray permeation device
X-ray control device
Q : In the past, there was a type of investigation using ultrasonic waves. In recent years, is X-raying mainly used?
Kanba : Nowadays, it is the most widely used equipment. I think it is an analyzing device which can obtain a lot of information in a relatively short time. Although there are other devices that have higher performance, they can only analyze limited parts of items and cannot analyze other parts. It might not be possible to conduct a high level of analysis with single X-raying, but X-raying is a highly suitable method for grasping an overall picture.
Q : What length of items can the instrument handle? Are items less damaged and affected by X-raying?
Araki : Two screens of a pair of six folding screens can be handled. It is possible to automatically move the tube and synthesize images into a single large X-ray image by computer. We do not X-ray many times at this level of analysis, so there is almost no effect on items.(continued in the next page)
X-ray radiation place
X-ray radiation place