When washing quartz crystals in acid, put the crystals in plastic mesh bags, such as grapes and cherries come in, and hang them in the acid by a wire hook. A number of them can usually be used at once and you can inspect them at will. Just remove and dip in clear water. If they are not ready, they can be dipped in acid again.
Always remember, all acid is to be used in a well-ventilated
area, preferably put of doors. Rubber gloves and goggles are
still good safety wear. (Add acid to water not the reverse.)