In building a good foundation get to know vitreous enamel flux.
Here I have created to share my enamel flux test plates.
Like any painting technique there are various primers for various jobs. In art of enameling we have quite a few fluxes but they produce various findings. You have heard of a car having the rust primer coat = flux, before the color coat, If you ever finish a beautiful wooden object you would have the sand and sealer = flux, before the varnish coat. And preparing metal to enamel is the same way, as an enamelist I have prepared an enamel flux test plate.
Enamels are reactive to metal, not all but 90% I would say. So flux coats are usually necessary, and there are several hardness of these fluxes from available manufactures.
Next, I know what does that mater? visit my thoughts, understand vitreous enamel flux, with my enamel flux test plates https://alohilanidesigns.com/vitreous-enamel-flux-comparison/