If the operator should allow the hyposulphite solution to run over the plate unevenly, it is quite likely that white or blue streaks would result. These it is impossible to remove without injury to the impression. Some, in order to prevent this, breathe over the surface, thus moistening it and putting it in a condition to receive the solution with greater uniformity.
The plate should be well washed with water before gilding.
Gilding, or Fixing the Image.--The next process to be given is that for fixing the image on the plate. This is done by precipitating a thin film of gold over the surface and is productive of the most brilliant effect when prepared immediately after the plate has been washed with water after the application of the hyposulphite solution, and before the plate has been allowed to dry.
When, however, the plate has been dried and allowed to stand for any time, before gilding, the hyposulphite wash should be applied as at first, in order to destroy any chemical coating that may have been formed on exposure of the plate to the air. For gilding the larger plates, we have a gilding stand so constructed that the plate can be put on a perfect level.
In practice, I prefer holding the plate with nippers, fastened at one corner.
Hold the plate in the same manner as in removing the coating;pour on the gilding, newly filtered, until the surface is wholly covered, and with the blaze of the spirit lamp, at least three inches high, apply it to the back of the plate, moving it about, that the surface may be heated with as much uniformity as possible. Continuing this operation, the surface will generally become covered with small yellow bubbles which soon disappear, leaving the image clear and distinct.
It is advisable to make use of a lamp having a sufficiently strong flame to produce the effect in a few minutes.
If after a first heating, it is found that the impression can admit of a greater degree of intensity, it might be heated anew;but that is seldom necessary, and often by trying to do too, well, the operator, if he persists in heating certain parts of the plate, may find the liquid dry up just above the flame, and inevitably cause a stain*; or else the blacks are covered with a film, or even the coating of gold may suddenly exfoliate, when small particles are detached from the plate.
The impression is then entirely spoiled, but the plate may be re-polished.
* This can be remedied, however, if it is immediately washed over with the same solution that is on the plate, so that the surface shall not become cool; continue for a short time to apply the lamp under, and agitate the plate slightly, and it will soon be free from all imperfections and give a fine clear tone.
It is not unfrequent that the surface assumes a dark, cloudy appearance.
This is generally the best sign that the gilding will bring out the impression with the greatest degree of distinctness.
Soon, the clouds gradually begin to disappear, and, "like a thing of life" stands forth the image, clothed with all the brilliancy and clearness that the combined efforts of nature and art can produce.
When in the operator's judgment the operation has arrived at the highest state of perfection, rinse suddenly, with an abundance of clean water, and dry as before described.
When an impression is dark, the gilding process may be longer continued;but when light, it should be gilded quickly, as lengthening the time tends to bleach the impression and make it too white.
