"I Wish to remove some painted blemishes that have been fired into a china plaque I have decorated," writes a correspondent, "and I am told that this can only be done by means of hydrofluoric acid, which, I believe, is dangerous. Will you tell me, please, how to use the acid and what safeguards to employ." It is true that hydrofluoric acid is the only thing that will accomplish what you want; but it is such a powerful mordant that we are inclined to say, do not use it at all, but send your plaque to some professional decorator and get him to remove the blemishes for you. How dangerous it is you may judge from the fact that when the professional decorator has occasion to use it, he wears a mask as a protection from the fumes, while the acid itself is such a powerful corrosive that it has to be kept in a gutta-percha bottle. You can imagine the effect of a drop of it on the flesh. If, after this caution, you still wish to experiment with the acid yourself, procure a small bottle of it. from the chemist - an ounce will cost but a few pence - and proceed as follows: - Dip a small quill or wooden toothpick into the bottle, taking up just a single drop, which rub on the spot of gold or colour you wish to remove. As soon as the stain comes off, wipe the acid off with a sponge, using water very freely.

Having duly warned you of the danger of an inexperienced person employing such a powerful mordant, we may add that the professional decorator uses it without apprehension, as, indeed, after a while, you may also, especially if you are accustomed to work in a laboratory.