Fig. 1.
Fig. 2. THE DRAWING
Fig. 3. THE PAINTING
Fig. 4. THE ETCHING
Fig. 5.
A little practice will determine just when the plate should be removed from the solution, either for examination or final cleaning. Soft brass or copper corrodes much faster than hard metal, which takes about three times longer, and the process of corrosion will require from twenty minutes to an hour, according to the temper of the metal and the strength of the acid solution.
The Acid Solution
To prepare the acid solution obtain a large, clear glass bottle and fill it quarter full of pure water; into this slowly pour an equal quantity of nitric acid, taking great care not to spill any of the acid, as it acts instantly and will eat a hole in any cloth it falls upon or spatters over. Wear old clothes and a canvas apron when mixing or handling the acid, and never be in a hurry to get results quickly by the reckless use of the biting fluid. If perchance the acid should touch the clothing, apply a few drops of ammonia to the spot immediately, to neutralize the acid and stop its action. The spot should then be sponged with clear water and no stain will be perceptible.
As the acid is added to the water (never add the water to the acid), shake it occasionally to thoroughly mix it, and let the mixture stand for a while to cool; then place a rubber cork in the bottle, label it Nitric Acid Solution—POISON, and place it beyond the reach of small children.
A solution that has been used should be poured from the tray into another bottle, to be used again by adding a small quantity of fresh solution. An old solution does not act as quickly as a new one, but for soft metal plates it is preferable, as it does not require such careful watching. The fumes of the acid, when at work, are disagreeable, so if possible it is well to carry out this part of the process in the open air. After the plate is immersed in the acid, do not handle it with the unprotected fingers.