When to use the Various Fluxes

Thompson fluxes are described under Enamelling Information on this website. 

Flux is only used under transparent enamels. For use on copper and guilding metal, I advise flux #2030. This flux is not always clear on the first firing as it absorbs the copper oxide, formed during the firing, but it will clear up on following or prolonged firings.
Flux #2020 was specially developed for use on silver. However, even under transparent enamels it is not always necessary to use flux. When making samples of transparent enamels, you could find out how the colour looks on the base material with and without flux.