I'm interested in understanding if we could get to a place of calibrating the extent of visible copper sulfide tarnish as a measure of hydrogen sulfide atmospheric concentration. My inclination is that it could first be used as a presence/absence indicator for a certain concentration threshold, which in itself would be very useful. Does anyone have ideas for the utility of a presence/absence indicator of this type? Does anyone know of other tarnish-based methods that are calibrated to indicated relative or absolute concentration?