Over time, I settled on simple wax as the resist and a solution of the cheapest vinegar I could find mixed with water (4 parts water to 1 part vinegar). This combo has proven to be the best for my uses together with a stout sponge and the right touch not to break the greenware.
Illustrated is a before and after picture of an etched porcelain teabowl. The etched design is of the kanji “JU” which represents long life or longevity. I refer to it as O-Ju, the Big Life, and it is bordered by a net design. The teabowl is glazed in my temmoku and haiyu glazes, which despite softening the visual of the design, the etched surface is very tactile and as a recent client commented, “it allows you to feel the JU”.