The cause of this appears to be, that with a moderate heat the chlorine
is merely set free from the gold, and remaining in the solution,
instead of being driven off, with its powerful bleaching, properties,
it immediately acts upon the shades of the picture. A dark impression
can thus, by a low heat, long-continued, be made quite light.
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.
Yet the operator is often, in fact most generally,
called upon to hide an excellent specimen under paint.
I can conceive of nothing more perfect in a Daguerreotype than
a finely-developed image, with clearness of lights and shadows,
possessing the lively tone resulting from good gilding.
Such pictures, however, are not always had, and then
color may perform the part of hiding the imperfections.
We present the following method as given in Willat's Manual:

"Daguerreotype portraits are now commonly met with beautifully colored;
but the coloring is a process requiring great care and judgment,
and many good pictures are spoiled in fruitless experiments.
Several different methods of coloring have been proposed.
The simplest mode appears to be that of using dry colors prepared
in the following manner: A little of the color required,
very finely ground, is thrown into a glass containing water,
in which a few grains of gum arabic have been dissolved.