Two Japanese woodblock prints chosen for the upcoming Chester Beatty exhibition Edo in Colour: Prints from Japan’s Metropolis, required significant conservation treatment before they could be exhibited.
Both prints, Cherry blossom viewing at Asukayama (CBL J 2823) and Enjoying autumn leaves (CBL J 2824), are in triptych format and were created by Katsukawa Shunchō, circa 1785-1789. When they came to conservation both triptychs were adhered to an acidic backing board that had caused discolouration and degradation.
In both cases, the woodblock triptychs consisted of three overlapping sheets of paper that had been firmly adhered to a 3mm thick millboard. This backing board is not original and was added in the nineteenth or early twentieth century, likely by a collector or seller in the West. When the prints were produced in the Edo period (1603 – 1868), triptychs were not fastened together or even necessarily bought as a set.  Instead triptychs, or sanmaitsuzuki, were carefully designed so that the composition of each printed sheet of paper worked both individually and as part of the whole.
Based on the variation in colour between the three sheets, for instance the differing greens of the grass, it is possible that CBL J 2823 is made up of prints from three different editions whereas CBL J 2824 has a much more uniform appearance, suggesting the prints may be from the same edition.
Backing art on paper with rigid materials gained popularity in the 19th century, when machine made paperboards became readily available. I have seen several objects across the collections in the Chester Beatty that have suffered from the addition of backing boards, adhered by well-meaning individuals under the illusion they will ensure flatness and offer increased durability. However, not only can these boards disturb the surface features and aesthetic of the original artwork, but they are also often poor quality and adhered with unsuitable adhesives. As conservators, we only intervene when it is clear that the backing board is damaging to the object: that is, it is visibly causing distortions, brittleness or discolouration to the artwork.
In this case the inner content of the board was clearly acidic as can been seen by the dark colour of the pulp and discolouration/yellowing of the adhered print. A test confirmed the board had an acidic pH of 4.5. The boards were also starting to delaminate at the corners. A dark yellow drip-shaped stain ran from the top of the print down into the centre on the right-hand panel of both triptychs – this was visible on both the recto of the print and the back board. Other damage included insect activity in the form of a series of holes at regular intervals, implying the triptychs were once stored rolled.
I wrote a treatment proposal and, after documenting the condition and taking photographs, the process of backing removal began. The backing boards were removed gradually one layer at a time using a rounded scalpel blade until the layer closest to the print was reached – this was a time-consuming process that required constant concentration. If too much pressure was applied the blade could cut too deep into the backing and damage the print. The historic labels stuck to the backing boards were removed intact and safely stored.
An overall wet treatment seemed like the best option to remove the final facing layer, reduce stains, and remove residual acidity from the prints.  Solubility testing was carried out to determine the viability of washing and spot testing showed that all of the colours were stable in both water and IMS. I also tested to check if the adhesive was water soluble which, luckily, it proved to be. Although the prints are on thin paper, Japanese paper is much stronger than many Western papers as it is made from organic material with a longer fibre length such as kozo. In addition, there wasn’t much mechanical damage, so I felt the triptychs could be safely washed.
Washing the prints was very much a team effort, and I worked with Julia over two days. Each print was humidified in a chamber for one hour, then spray humidified using 50/50 IMS and water to help with absorption and even wetting. It proved quite challenging to get the prints to wet out evenly, possibly due to a coating on the remaining backing paper. However, with the addition of IMS and perseverance we were able to achieve it!
The prints were float washed for 15 minutes. We checked the pigments throughout to make sure there was no movement of media as spot testing is not absolute and cannot completely predict how colours will react when exposed to high levels of moisture for an extended period of time. Handling the triptychs when wet was challenging due to their size, so it was important that Julia and I worked together to move the print in and out of the water bath.
After allowing the triptych to drain off on the drying rack for a minute, we placed it face down on a clean, flat surface and removed the final layer of backing with spatulas. Even with two of us working together this process took us about three hours per triptych! It was very satisfying to see the print slowly being revealed. We regularly sprayed the print to keep it wet and covered areas not currently being worked on in polythene to trap the moisture and prevent the print from drying out until all the backing was removed.
After the backing was removed, we again float washed the triptychs for a final 15 minutes to remove any residue of adhesive or acid before finally drying the prints under light weights between Bondina, blotter and felts. Once dry they were hinged into bespoke window mounts with Japanese paper, ready to be exhibited.
The backing removal was a long and careful process but overall it was very successful. On both prints, the dark yellow stain running from the top down into the centre on the right-hand panel was much reduced through washing, and the prints appear brighter. It was not possible to separate the individual triptych panels, which had been strongly adhered before they were backed. However, both triptychs are now safely remounted in 100% cotton mounts, where they will remain safe from acidity and damage for the future.
To see photos of the triptychs after conservation and high-quality images of more artworks and manuscripts from the collection, please visit Chester Beatty’s digital collections. We hope you will be able to visit the exhibition Edo in Colour: Prints from Japan’s Metropolis, when the museum reopens but for now please enjoy the online exhibition. The beautiful exhibition catalogue by Mary Redfern, Curator of the East Asian Collection, is also available now!
Sophie Coulthard, Conservation Intern 2019/21.
 For more about the triptych format in Japanese Woodblock Prints, see:
 To learn more about aqueous treatment in conservation and the interactions between paper and water, this is the book to read: ‘Paper and Water: A Guide for Conservators’ by Gerhard Banik and Irene Brückle, London: Routledge Series in Conservation and Museology, 2011.