比黄金还珍贵的颜料，到底是怎么消失的？(2)

群青色，是将阿富汗出产的天青石研磨成细粉，然后与油和蜡混合而成的蓝色颜料。这种蓝色颜料是文艺复兴时期画家使用的最昂贵的蓝色，比黄金还要珍贵。直到人工合成的群青色于1826年得以发明，群青色的价格才跌下神坛。
Ultramarine sickness – which results in the paint becoming a dulled（使变得无光泽的） grey-blue colour – occurs in both the natural and synthetic versions of the pigment. Previously, researchers assigned the malady（疾病） either to pigment loss or to tiny cracks forming between pigment particles and organic（有机的） binders（粘合剂） in the paint causing light to scatter（使分散） and dull the perceived colour – despite the blue pigment still being there.

群青综合症，会导致颜料变成暗淡的灰蓝色，这种情况在天然和人工合成的群青色颜料中都会发生。此前，研究人员将此归咎于颜料丢失或颜料颗粒与有机粘合剂之间的细小裂缝，认为这些裂缝导致光线分散并使人们感知到的颜色变暗——尽管蓝色颜料仍然存在。
‘If you look at the structure of ultramarine it makes complete sense it has catalytic activity, as it is a zeolite（沸石） and analogous（相似的） to commercial catalysts,’ explains Katrien Keune at the University of Amsterdam, Netherlands. The zeolites could be responsible for the pigment’s ‘disease’ by degrading the binder to produce the light scattering effect.