I have the same question and have been experimenting. I assume you are drawing your own artwork. I tried spray lacquer...worked ok but hard to see my artwork in progress since it is clear. I have had good results with non-spray resist....for fine lines, I have pretty good luck using my wife's lipstick as resist....but if you smudge your completed art work it is "do over". I have also used silkscreen acrylic ink as a resist, etching my design after it drys. This solved the smudge problem but it tends to flake if it is too thick. Latest attempts have been 50/50 melted beeswax and asphaltum varnish....this works reasonably well but flaking is still a problem. If you are using stencils or computer generated designs, folks on some artistic forums talk about this stuff called "press n peal blue paper". You print the design on the paper, iron it onto the metal, and the ink acts as a resist....I have not tried it yet but plan to. If you know of any other resists that work, I am all ears as I have not yet found the "perfect" one.
