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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.
Gradually they turn to a darker shade; the reddish tint becomes lilac, purple, brown, of somewhat different tints in different cases. When the process seems to have gone far enough, the picture is thrown into a bath containing hyposulphite of soda, which dissolves the superfluous, unstable compounds, and rapidly clears up the lighter portions of the picture.
Almost at his elbow is a toning bath, but he would think it a good joke, if you asked him whether a picture had lain long enough in the solution of gold or hyposulphite. We always take a glance at the literature which is certain to adorn the walls in the neighborhood of each operative's bench or place for work. Our friends in the manufactory we are speaking of were not wanting in this respect.
The reagents are solution of mercury iodo-chloride prepared by dissolving of 25 grms. iodine, 500 c.c. alcohol of 95 per cent., and of 30 grms. mercury chloride in an equal measure of the same solvent; both liquids are filtered and united; a standard solution of sodium hyposulphite produced by digestion of 24 grms. of the dry salt with 1 liter water and titration with iodine solution; solution of potassium iodide of 1:10; chloroform, and finally a solution of starch.
I prepare this salt as follows: Dissolve one part chloride of gold and four parts hyposulphite of soda in equal quantities of distilled water: pour the gold into the hyposulphite solution, in the same manner as in mixing the gilding solution; let it stand until it becomes limpid; filter and evaporate to dryness. Re-dissolve and add a few grains of burnt alum.
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.
Apply a gentle heat, and soon the spots disappear, leaving the impression clear and free from all organic matter. In the absence of cyanide of potassium, a solution of pure hyposulphite of soda will answer as a fair substitute. To Redeem, a Solarized Impression. The Daguerreotype plate, prepared in the ordinary manner, should be exposed in the camera a sufficient time to solarize the impression.
The paper, having the picture formed on it, is then washed with the solution of hyposulphite of soda, rinsed in pure water, soaked again in a solution of hyposulphite of soda, to which, however, the chloride of gold has been added, and again rinsed. It is then sized or varnished.
To procure the best effect, then, heat suddenly with a large blaze, and judging it to be at the maximum, cool as suddenly as possible. When the hyposulphite of gold is used instead of the chloride, a less heat should be employed. Coloring Daguerreotypes. Of all the so-called improvements in the Daguerreotype, the coloring is the least worthy of notice.
Then we replace the slide in the shield, draw this out of the camera, and carry it back into the shadowy realm where Cocytus flows in black nitrate of silver and Acheron stagnates in the pool of hyposulphite, and invisible ghosts, trooping down from the world of day, cross a Styx of dissolved sulphate of iron, and appear before the Rhadamanthus of that lurid Hades.
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