Conserving a woodblock print by Torii Kiyomasu I
A sound understanding and knowledge of the traditional pigments and techniques used in the production of Japanese colour woodblock prints is required when considering conservation treatment. This print by Torii Kiyomasu was produced from a single impression in black and white. The black pigment used in the print is called sumi and is made from soot and incense. Moulded into bars bound with animal glue, sumi can be softened with water to produce a very stable pigment. The red colour, later hand painted onto the printed sheet, is made from lead, saltpetre and sulphur. The colour is called tan and gives its name, tan-e, to this type of print.
By the mid-eighteenth century multicoloured prints were made from both finely ground inorganic pigments, for example shu (vermilion) and gofun (ground oyster shell), and organic pigments, for example beni (safflower - red) and ai (indigo). These organic pigments are known to be light and alkaline sensitive. It is common to see a purple colour, a combination of aigami (blue) and beni (red) fade to a pale brown from exposure to daylight. These colours are also moisture sensitive, which would prohibit any conservation wet treatment. Because the pigments are so soluble in water they could completely disappear.