At the end of this time, wash and examine again. Even now everything will be intact. With very fine drawings, however, lateral action has already progressed so far that, under all circumstances, the exposed edges must be covered. Coarser drawings generally stand one or two minutes more.
To try the depth of etching: with your finger-nail on the edge of the black {85} rim, feel how far the etching-on has proceeded. As soon as the finger-nail catches, the depth is sufficient, and the sides of the lines may be covered.
For this operation the plate needs, above all, thorough washing, drying on both sides by blotting-paper and gentle heat, and a temperature of 45° C. At this temperature place the plate into the finest resin-powder, and rub the latter several times over the warm drawing, using for this purpose a fine brush. The protection, which has grown sticky through heating, retains a thin coating of resin, which, after dusting off the bright metallic spots with a brush and fine cotton, and after careful fanning off, is reheated to about 50° C. At this temperature the plate is returned to the white rosin, receives a good dusting-in, and being freed from excess as before, is heated to about 65°, so that the easily fusible rosin begins to spread out. At this moment extinguish the light, and put the plate into the asphaltum, which will attach itself copiously to the sticky resin. Brush the plate well with the substance, remove any excess from the bright spots, heat to 80° C.; then place it again into the asphaltum, brush it, clean it by removing any excess, and heat it to 100° C., when a complete combination of the resinous mass takes place, and a uniform etching varnish is formed. This last coating is extremely regular, and it is wonderful to see the accuracy with which the lines have been covered. Beginners are warned to pay attention to the careful cleaning of the bright parts of the plate when brushing and dusting it; should any resin remain behind, it melts on, and grows by degrees to a strong yellow tint, which is very difficult to remove, but very easy to guard against. Never forget to dust off the back.
While the plate is still hot, lean it against the wall, face in, and the back covered with a solution of shellac.
Now the plate is ready for further etching, which is carried on for two minutes in the first bath. At the end of two minutes, wash and examine critically. In almost every case we may etch for a third, or even a fourth time. It is, however, sufficient for the beginner to know that he has sufficiently etched in two spaces of two minutes each, after preparing with resin. Trying and examining with the finger-nail on the black edge will show a fine relief. Should it be possible to etch for a third space of two minutes, or even of one, without danger, it is preferable to do so. It should be a rule to proceed as far as possible, judging from the character of drawing and coating. Experience is easily gained in two or three trials, since anything can be examined at any moment. Beginners would do well to use a magnifying-glass with good field of view in examining, when they can observe the most sensitive portion, and {86} all changes may easily be noticed. The brush should be used lightly, to prevent scratching. Usually, it is fastened at right angles to a stick to protect the hands from the effect of the acid.
To raise the plates out of the tray, lay a gutta-percha thread into the bottom of each tray, fastened at one end to the top edge of the tray, projecting over the same on the other side. The plate is placed on the thread while etching. It may be removed without touching the bath by pulling the free end of the thread.
As already remarked, the spreading of ink on a surface which is more or less rough is difficult. For this reason the plate, when etched-on after my method, is to be washed out with oil of turpentine. A strong brush should be used for this, and some of the oil rubbed over the plate without pressure. You must cause a dissolving, not a rubbing off, of the coat. On continuing the addition of turpentine, the metal grows bright. Take, then, a handful of the coarsest of pine-wood sawdust and rub off the surface. This removes instantly every trace of turpentine, leaving a clean surface behind. For the sake of security, pour on more turpentine, rub with a somewhat softer brush, and remove again with clean sawdust.
It is important that the wash-table should always remain free from sawdust, which latter should fall through the grating into a suitable receptacle. If this rule is disregarded, the wash-brush will soon be a conglomerate of sawdust and hairs. Sawdust and turpentine will stick to the brush so tightly that a new brush will have to be purchased.
Now we again examine our work. It is a mark of success if the relief still shows its original smoothness in all its parts, and has nowhere grown porous. All the parts must be clear in their correct proportional strength, as seen in the transfer.
The treatment of the plate from the time of transfer to the close of the etching-on takes: for the saving of the edges and the white portions of the drawing, 2 minutes; for preparing twice with asphaltum, 4 minutes; for varnishing the back and coloring the plate, 4 minutes; for etching-on the lateral protection, 4 to 5 minutes; for preparing twice with resin, asphaltum, and varnishing, 16 minutes; for renewed etching, 4 to 5 minutes; and for washing, 5 minutes—that is, 33 minutes in all. Add 7 minutes for inspection and retouching, and 40 minutes will be the space allowed for etching-on. {87}