Aloha Sally, The enamels should be ok.The best thing is do some
test tiles on copper or silver to check the colors for
contamination and to show the true fired colors.My concern would
be lead bearing enamels,as the fumes are hazardous to ones
health.The enamels being 30 years old,the possibility is
assured.Though,nothing a good vent hood couldn’t corrrect.As far
as ceramit is concerned,don’t bother.It’s a heat cure epoxy
material,that gives the illusion of an enamel.You mix it my
weight(a pain unto itself) and cure it in an oven or under a
heat lamp.The result is a colored(opaque or transparent) epoxy
finish and can be polished(to the point of errosion)on a
polishing wheel.Better to use on materials,not able to withstand
the vitreous enameling process(if worth the effort).Besides you
may have to do work on the piece again,one day.Just my humble
opinion. Regards, Christian Grunewald Hawaii