or two results which I retained as curiosities till only a month or two
ago; but up to that time I cannot say they had faded in the least, and I
have here a specimen made three years ago, which I have purposely
subjected to very severe treatment. It has been exposed without any
protection to the light and damp and all the other noxious influences of
a Glasgow atmosphere, and although certainly tarnished, I think you will
find that it has not faded; the whites are dirty, but the blacks have
lost nothing of their original strength. I here show you the picture
referred to, a 12 by 10 enlargement on artist's canvas, and may here
state, in short, that my whole experience of argentic enlargements leads
me to the conclusion that, setting aside every other quality, they are
the most permanent pictures that have ever been produced. Chromotypes
and other carbon pictures have been called permanent, but their
permanence depends upon the nature of the pigment employed, and
associated with the chromated gelatine in which they are produced, most
of pigments used, and all of the prettiest ones, being unable to
withstand the bleaching action of the light for more than a few weeks.
Carbon pictures are therefore only permanent according to the degree in
which the coloring matter employed is capable of resisting the
decolorizing action of light. But there is no pigment in an argentic
print, nothing but the silver reduced by the developer after the action
of light; and that has been shown by, I think, Captain Abney, to be of a
very stable and not easily decomposed nature; while if the pictures are
passed through a solution of alum after washing and fixing, the gelatine
also is so acted upon as to be rendered in a great degree impervious to
the action of damp, and the pictures are then somewhat similar to carbon
pictures without carbon.

I may now say a few words on the defects and failures sometimes met with
in working this process; and first in regard to the yellowing of the