Etching china with hydrofluoric acid or ammonium fluoride or other fluor components.
Hydrofluoric acid is the most dangerous acid even in low concentrations. Using Hydrofluoric acid is very dangerous, Latex or house hold gloves are not safe enough, you need special gloves, a face mask and a special exhausting cabinet for the vapour. In case of contact with your skin directly apply lots of calcium-gluconate gel (2 or 3 %) at least for 2 hours. It harms your lungs terribly, goes through your skin and bones and the wounds heal slowly. The fluor ion attacks the calcium balance in your system giving delayed heart problems. And all that risk for a lousy piece of porcelain. Be wise and take a new piece of porcelain and paint again. When you can paint it one time, you can do it again. When you harm your lungs or hands you cannot replace them. Furthermore look at the following site for deadly accidents with Hydrofluoric acid!http://www.safetyline.wa.gov.au/pagebin/injrsign0079.htm

For medical information See; http://www.emedicine.com/emerg/topic804.htm
Hydrofluoric acid, in pure form, is banned in the US as far as able to buy it over the counter. It used to be used to etch china, but it cannot be bought by individuals now and can only be used in industrial situations by professionals. However, small amounts are still in a products like “Whink” and rust removers like Rustiban and also in “China Eraser”. In “Etchall” the active compound is ammonium fluoride which is less dangerous, but also care must be taken.