It will be plain to you, from what I have just said, that the operation you are about to engage in is one of the most delicate in the etcher's practice. There is the plate in the acid; the liquid has taken hold of the copper; but your sky must be light, and a prolonged corrosion would therefore be hurtful to it. Hence we take the plate out of the bath, pass it through pure water, so that no acid is left in the lines, and cover it with several sheets of blotting-paper, which, being pressed against it by the hand, dries the plate. We shall have to go through the same process after each partial biting, because if the plate were moist, the stopping-out varnish which we are going to apply to it would not adhere.
32. The Use of the Feather.—You noticed the lively ebullitions on the plate, which took place twice in succession. After the first, I passed this feather lightly over the copper, to show you its use. Its vane removed the bubbles which adhered to the lines. This precaution is necessary, especially when the ebullitions acquire some intensity and are prolonged, to facilitate the biting, as the gas by which the bubbles are formed keeps the acid out of the lines. If these bubbles are not destroyed, the absence of biting in the lines is shown in the proofs by a series of little white points. Such points are noticeable in some of the plates etched by Perelle, who, it seems, ignored this precaution.
33. Stopping Out.—The two rapid ebullitions which you saw may serve you as a standard of measurement; the biting produced by them must be very light, and sufficient for the tone of the sky. You may, therefore, cover the entire sky with stopping-out varnish by means of a brush, taking care to stop short just this side of the outlines of the other distances. The importance of mixing lamp-black with your stopping-out varnish to thicken it, comes in just here; because if it remained in its liquid state, it might be drawn by capillary attraction into the lines of those parts which you desire to reserve, and thus, by obstructing them, might stop the biting in places where it ought to continue. Wait till the varnish has become perfectly dry; you can assure yourself of this by breathing upon it; if it remains brilliant, it is still soft, and the acid will eat into it; but as soon as it is dry it will assume a dull surface under your breath.[8]
34. Effect of Temperature on Biting.—Let us now return the plate to the bath, to obtain the values of the other distances. The temperature has a great effect on the intensity of the ebullitions, and it is hardly possible to depend on it absolutely as a fixed basis on which to rest a calculation of the time necessary for each biting, as its own variability renders it difficult to appreciate the aid to be received from it. In winter, for instance, with the same strength of acid, it needs four or five times as much time to reach the same result as in summer, so that on very hot days the biting progresses so rapidly that the plate cannot be lost sight of for a single moment without risk of over-biting.
Pl. Ia.
35. Biting continued.—We have now obtained several moderate ebullitions, and as it would not do to exaggerate the tone of the mountain in the background, it is time to withdraw the plate once more. Uncover a single line by removing the ground, either with the nail of your finger or with a very small brush dipped into spirits of turpentine, to examine whether it is deeply enough bitten for the distance which it is to represent. If the depth is not sufficient, cover it with stopping-out varnish, and bite again. This is not necessary, however, in our present case, and you may therefore stop out the whole background. Remember, if you please, that the line must look less heavy than it is to show in the proof; for you must take into account the black color of the printing-ink. With your brush go over the edges of the trees which are to be relieved rather lightly against the sky, as well as over that part of the shadow in this tower which blends with the light. There are also some delicate passages in the figure of the woman in the foreground, in the details of the plants, and in the folds of this tent ([Pl. Ia]). Stop out all these, and do not lose sight of the values of the original ([Pl. II.]). Make use of the brush to revarnish several places which are scaling off on the margin and the back of the plate. The temperature is favorable; the ebullitions come on without letting us wait long, and the plate is bluing rapidly. I do not like to see these operations drag on; in winter, therefore, I do my biting near the fire. We soon acquire a passion for biting, and take an ever-growing interest in it, which is incessantly sharpened by thinking of the result to which we aspire. Hence the desire of constant observation, and that assiduity in following all the phases of the biting-in.
I notice that the acid does not act on certain parts of your work; you will find out soon enough what that means.
36. Treatment of the Various Distances.—“I am thinking just now of what you told me in regard to the background:—that more work ought to be put into it than into the foreground.”