Though the effect cannot be reproduced on screen, it is interesting that that Bi oxychloride displays a deeper luster than guanine, the natural substance recovered from fish scales it replaces. It is in more plentiful supply, less costly too.
Some pigments are thermochromic .
The color changes as a function of temperature to indicate that a glassy or ceramic surface is not safe to the touch for instance. Color indicators investigated for frozen food packaging confirm that the contents have been kept within a safe temperature range. Invisible to the naked eye, but reassuringly detectable to X-rays, Bi additions to polymers for catheters, tooth fillers or bone inplants for human health care and a growing array of diagnostic systems. Bi compounds protect credit cards and similar financial instruments against forgery. Equally discrete, it is the Bi-containing amalgam inside energy saving lighbulbs which gives off a warm color tone rather than the deep red of sodium vapor lamps illuminating highways.