12. Etching Points or Needles, for scratching the lines into the ground. Rat-tail files of good quality, costing about twenty cents each at the hardware-stores, are excellent for the purpose. Two are all you need for your experiment, and even one will be sufficient. Still cheaper points can be made of sewing, knitting, or any other kind of needles, mounted in sticks of wood like the lead of a lead-pencil. Use glue or sealing-wax to fasten them in the wood.
13. An Oil-Stone for grinding the points.
14. An Etching-Tray to hold the acid during the operation of biting. Trays are made of glass, porcelain, or india-rubber, and can generally be had at the photographer's supply-stores. A small india-rubber tray, large enough for your experiment, measuring four by five inches, costs fifty-five cents. But you can make an excellent tray yourself of paper. Make a box, of the required size and about one and a half inches high, of pasteboard, covered over by several layers of strong paper, well glued on. If you can manage to make a lip or spout in one of the corners, so much the better. After the glue has well dried pour stopping-out varnish into the box, and float it all over the bottom and the sides; pour the residue of the varnish back into your bottle, and allow the varnish in the box to dry; then paint the outside of the box with the same varnish. Repeat this process three or four times. Such a tray, with an occasional fresh coating of varnish, will last forever. For your experiment, however, any small porcelain (not earthenware) or glass dish will do, if it is only large enough to hold your plate, and allow the acid to stand over it to the height of about half an inch.
15. A Plate-Lifter, to lift your plate into and out of the bath without soiling your fingers. It consists of two pieces of string, each say twelve to fifteen inches long, tied to two cross-pieces of wood, each about six inches long, thus
. It is well to keep the fingers out of the acid, as it causes yellow spots on the skin, which remain till they wear off.
16. Nitric Acid for biting in the lines. Any nitric acid sold by druggists will do, but the best is the so-called chemically pure nitric acid made by Messrs. Powers & Weightman, of Philadelphia. It comes put up in glass-stoppered bottles, the smallest of which hold one pound, and sell for about sixty cents.
17. Water for mixing with the acid and for washing the plate.
18. Blotting-Paper, soft and thick, several sheets, to dry the plate, as will be seen hereafter.
19. Spirits of Hartshorn or Volatile Alkali.—This is not needed for etching, but it is well to have it at hand, in case you should spatter your clothes with acid. Spots produced by the acid can generally be removed by rubbing with the alkali, which neutralizes the acid.