The combination of gum and gallic acid is broken up by this etching in all those places which were not protected through the transferred drawing, and the latter itself, in the subsequent blackening with chemical India-ink, forms the coating and protection against a combination of the zinc below. It is best to blacken it with a brush and to warm the plate until the ink has become dry. Now moisten again with gallic acid and gum, wash the plate (without great pressure) with spirits of turpentine, rub on more of the solution of gum, and blacken as usual. Practice will insure safe working by this method.—J. O. MORCH.
ETCHING APPARATUS.
It does not come within the province of this work to instruct in the preparation of inks and colors for etching or for printing, since such articles are better purchased of the dealers ready prepared. In all cases the choicest results are obtained by using the best apparatus and the purest materials. There is no economy in “getting on” with the “cheap.”
A few hints as to some of the “tools” which are found convenient in practice: For sifting the fine resin dust, a machine is employed, known to sieve manufacturers as “the composition sieve.” It consists of the ordinary sieve, having on each side a cover with a bottom of calf skin. The sieve-bottom is made of the finest silk texture. (See Fig. 10.)
For fixing and melting-in of the drawing on metal, I use a grate made of a wooden frame with diagonal iron rods. This form is preferable to the ordinary grate, because it allows the flame free access to the metal plate. Inasmuch as the heat is strongest in the centre, the cross-bars protect the centre of the plate from burning and from warping. The source of heat is either an alcohol {98} lamp (Fig. 11) in which cotton soaked in alcohol is ignited (the cover shown in the drawing serves to smother the flame), or a strong gas flame (Bunsen burner). The adoption of the latter mode is advisable.
| Fig. 10. The Sieve. | Fig. 11. |
Formerly I employed a plain cast-iron heating-plate, with a gas or a petroleum flame. The zinc plate, however, being in direct contact with the hot surface, warped very much. I obviated that somewhat by covering the heating-plate with a piece of wire-gauze. The strata of hot air thus obtained between the cast-iron and the zinc plate heats the latter equally throughout, and prevents warping. Still I prefer the direct method.
For freeing the plate from resin-dust, employ a strong pair of ordinary bellows.
The table (Fig. 12) for washing the coating material from the plate consists of a heavy framework, upon which rests a wooden grate. A massive table-board is not to be recommended, as the dirty sawdust adheres to the same, while with the other it easily falls through the openings into a box, and leaves the table free and clear.