About nine months since we directed attention to the system of colored
photography invented by Mr. J. E. Mayall, London. Since that time, Mr.
Mayall has further developed the details of his process, and as a result
his color pictures have been much improved both as regards appearance and
size, and are beautiful specimens of this new departure in photographic
art. As stated in our previous notice, Mr. Mayall, after fourteen years of
experimental research, has discovered the art of reproducing the colors
latent in the negative of the photograph, having arrived at his discovery
by the aid of spectrum analysis, which led him to the conclusion that
every color in the organic world, when exposed to a suitable photographic
plane in a camera, registers exact vibrations. Mr. Mayall has succeeded in
producing chemical colors extremely attenuated, which exactly correspond
with the vibrations in the negative. In doing this, he keeps the film
alive to the smallest vibrations of light. He uses, first, lactate of iron
to impregnate the isinglass film with a salt of iron capable of uniting
with any stronger organic acid; and, secondly, meconic acid, which
impregnates the film of albumen, and has a stronger affinity for iron than
lactic acid. It unites with the iron, and forms a red film, which is in a
state to receive all the lower vibrations of the red end of the spectrum,
and this gives these lower vibrations a fair chance with the electric
light. All subsequent processes assist this chemical march to the final
end of making a print that will take up colors, which, when added, fall in
their places, and there remain indelible and unalterable.--_Iron._