This keeps a constant etching strength while conserving resources and minimizing waste. The mixture actually forms weak hydrochloric acid which lightly etches the surface, removing oxidation. Some people use vinegar or soy sauce instead of pure acetic acid, but the impurities complicate resist laydown in photogravure. A good working solution is eight parts water to one part each of acetic acid and salt by volume. Skin and eye contact with NaOH are dangerous, but it is not volatile.
Rubber gloves are essential for mixing and using sodium hydroxide.
Small quantities of sodium hydroxide can safely be poured down the drain, as it is the active ingredient in drain cleaner. Ammonia is highly corrosive to the eyes. These substitutes require more effort to remove etching ink, but are non-volatile and safe to use. Organic Solvents . Organic solvents, used in cleaning up inks and etching grounds, are among the most common and insidious poisons found in the printmaking workshop.