steel something like a lead pencil, sharpened to as
fine point. A darning-needle, or anything in tlie
shape of a piece of steel will do, only the sharpening
of the point is all important. Sharp it must be, but perfectly round and smooth, to run easily over the
plate in any direction. Now he takes the cold plate and explains that wherever he scratches through the ' ground ' and lays bare the copper, there the acid will attack it and bite in a furrow, deeper and jcider the longer it is allowed to act ; but where the ground remains, the copper is perfectly protected. So he scratches a little sketch on the plate, and then writes our names on it — backwards, of course, because all blue green colour, owing to the copper dissolved in it taking the form of nitrate of copper.
When the acid is mixed fresh with ordinary water it gets very hot, owing to its action upon the impurities of the water ; and it is necessary to wait till it gets cool again, or it would bite too fast, and probably break through the ground.
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The varnish being now dry, he slips the plate into the bath, and in a few moments the lines whicii showed as gold upon the black ground turn green and give off bubbles of gas. The quantity of bubbles given off is the best guide, in this bath, of the depth the lines have gone. Of course the time a plate is in proofs, either from a plate or block, come the reverse way — that is, the right hand side of the proof comes from the left side of the plate. It is surprising how easy it is to write backwards, and in drawing anything on the plate which will suffer by printing reverse, it is usual to draw from the reflection of the thing in a looking-glass.
He now paints the back of the plate with ' stop- ping out ' varnish (generally Brunswick black thinned with turpentine) to prevent the acid from attacking it thei'e, and utilises the few minutes it is in drying, by explaining the acid bath. There are several baths or ' mordants ' used for biting, but this one is a nitrous acid bath, made of half acid and half water, more or less, a weaker bath taking longer to eat away the copper, but giving a cleai-er line. The liquid is in a porcelain dish, and is of a beautiful the bath is some guide, but not much, because the temperature of the room, and the quality of the copper, and the strength of the bath, are always altering, and affecting the speed of the biting. So after the bubbling has gone on a few minutes, he fishes the plate out again, washes it under the tap, and dries it with blotting-paper. Now the lines which he wishes to be lighter than the others he paints over with a brush dipped in the same varnish as that with which he painted the back of the plate, and of course this, when dry, protects them from further action of the acid. Then it is put in the bath again, and the remainder of the lines get deeper and wider. And of course this ' stopping-out of parts, as it is called, can be carried on to any extent, so as to get a great range in the depth of the lines. But this being an experimental plate,
