The ferrotype and how to make it - The Grian Press

92 THE FERROTYPE.
not felt the action of light, remain as opaque as
before exposure, and with very little if any change
of color, remaining in the same state as when
taken from the bath, that is, iodide of silver ;
but the image, which now stands out plainly, ia
composed of metallic silver in the light and in-
termediate part, and iodide of silver in the shad-
ows. If the plate is now immersed in a solution of
cyanide of potassium (which is a powerful solvent
of the iodide of silver), it will at once be dissolved
and removed, leaving the image, which is in the
light parts metallic silver, in the dark parts the
black surface of the plate showing through the col-
lodion film; so that the action of light in the
camera is to produce on the surface of the sensit-
ized plate, an image of the object in focus in
metallic silver, which serves as a basis upon
which to deposit more metallic silver in the pro-
cess of development. And as metallic silver in
this process will not deposit itself except upon a
metallic surface, we can easily understand why an
image may not be developed upon an under ex-
posed plate, as the exposure will not have been
of sufficient duration to have formed a basis. An
over-exposure, in like manner, will have destroyed
the proper gradations by extending the primary
change into the shadows.
The development of the latent image comes
second only in importance to the posing and
lighting of the subject preparatory to the ex-
posure of the plate, to which I concede the first