I found other examples of non-float glasses which react to short wave ultraviolet light. The reaction in the pressed jewel above is a result of the chemistry of the glass and not because of a tin coating. Can ultraviolet light be used as an indicator of how a particular glass reacts to silver stain?
Mouth-blown glass from St. Just shows a mild fluorescence compared to the Lambert's sample which shows no reaction.
Bullseye's "Reactive Ice" shows a strong fluorescent reaction. It also proved very reactive to stain.