Edingthorpe Rectory, Norfolk.
_New Effect in Collodion Pictures._--In the course of some experiments I
have been following in reference to a photographic subject, a method by
which a new effect in pictures on glass may be obtained has occurred to me.
Such productions, when treated as positives, are of course white pictures
upon a black ground; and although for beauty of detail they are superior to
those belonging to any other process, there is a certain harshness and want
of artistic effect: to remedy this, I turned my attention towards obtaining
a dark picture upon a light ground, as is the case when glass photographs
are printed from; in this I have succeeded, and as the modification affords
a pleasing variation, it may be acceptable to the tastes of some of your
readers. The principle I proceed upon is to copy, by means of the camera,
from a previously-taken picture in a negative state. Suppose, for instance,
our subject is an out-door view: I take a collodion picture--which would
answer for a positive if backed with black: this, viewed by transmitted
light, is of course negative,--an effect which may be produced by placing a
piece of white paper behind it from this _white_-backed plate: I take
another collodion picture, which, being reversed in light and shade, is
negative by reflected light; but viewed as a transparency is _positive_,
and of course retains that character when backed with white paint, paper,
or other substance lighter in colour than the parts formed by the reduced
silver. Instead of the first picture being formed by the glass, any of the
paper processes may be adopted which will afford negative pictures. Copies
of prints may be beautifully produced on this principle by obtaining the
first or negative by the ordinary process of printing. As these pictures
are to form a contrast with a white ground, they should be as brown in tint
as possible; nitric acid, or other whitening agents, being avoided in the
developing solutions for both negative and positive. By this process the
detail and contrasts can be kept far better than by the operation of
printing: for it is exceedingly difficult to obtain a picture which will
convey to the prepared surface an amount of light corresponding to the
natural lights and shades, and the trouble of making collodion copies is
far less than printing. There is certainly the drawback of having the
copies upon glass: I think, however, that some white flexible substance may
be found, upon which the collodion, albumen, &c., may be spread; but if
they be intended for framing, of course they are better on glass. The
general effect is that of a sepia drawing. The picture first taken and used
as a negative, may be preserved as a positive by removing the white back,
and treating it in the usual manner.
Permit me to observe, that much confusion arises from the _manner_ in which
the terms positive and negative are often used; a negative glass picture is
frequently spoken of as a definite, distinct thing; this is not the case,
for all photographic pictures upon glass are both negative and positive,
accordingly as they are seen upon a back of lighter or darker shade than
the reduced silver--by transmitted or reflected light. A picture intended
to be printed from is no more a negative than another, its positive
character being merely obscured by longer exposure in the camera. When
first removed from the developing solution, glass pictures are negative,
because they are seen upon the iodide of silver, which is a light ground.
This is a thing of course well known to many of your readers, but beginners
are, I know, often puzzled by it.