The article describes a historic Japanese green pigment which was identified in a painting attributed to the Kano school, dating to the Edo period. According to literature, malachite–which is the common translation of the Japanese term rokushō–has been the most widely used green pigment in Japan over a long period of time. Its colour shade could be modified by the use of different degrees of grinding and by heating the pigment. The green paint layer found in the painting was examined using XRF, SEM-EDS and XRPD, and cross sections. Examinations revealed a heterogeneous paint layer which consists of a mixture of various natural copper-containing minerals, some of which also contain arsenic and other elements. A concluding discussion of pigment nomenclature in Japan raises the question if rokushō may in fact be equated with pure malachite.
The aim of this research was an investigation into creating a rigid gel application of benzotriazole (BTA), a complexing agent, as a new potential way of treating verdigris-damaged paper. Various gel recipes were mixed and tested on historical samples. The gel recipes varied in gellan gel concentration, BTA/solvent solution concentration, and BTA concentration. The recipe effectiveness was assessed using Hulthe’s indicator paper and MQuant™ Test Cu indicator strips, two types of indicator papers which detect free copper ions. The results showed that rigid gel application of BTA is effective in complexing the copper ions which may inhibit further damage to the paper caused by free copper ions. Some of the other effects of the gel were the simultaneous removal of paper discolouration by the gel. Further research is needed to refine the gel recipes as well as the treatment process to prevent or reduce potential tidelines and other possible negative side-effects of gel treatment.