In the first place, we will take up for consideration the positive
process.
The first positives on glass were called ambrotypes, and were the
successors to the daguerreotype, which they superseded and displaced
by the superior facility of their production.
For the same reason the ambrotype was succeeded by the ferrotype,
which was a positive collodion picture, made on a thin iron plate
with a black japanned surface.
The ferrotype or tintype is now about the only product of the
positive collodion process of considerable importance, and is the
only one that will receive consideration in these pages.
Ferrotype plates are sold by all dealers in photographic materials;
they are mostly manufactured by two large concerns in Worcester,
Mass. [p016]