Early Work In Photography
A Text-book For Beginners
Forfatter: W. Ethelbert Henry C. E., H. Snowden Ward
År: 1900
Forlag: Dawbarn and Ward, Limited
Sted: London
Udgave: 2
Sider: 103
UDK: IB 77.02/05 Hen
Illustrated with an actual negative and positive, and numerous
explanatory diagrams throughout the text
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CHAPTER V.
FIRST LESSON IN DEVELOPMENT.
Lantern Slides.
Required for this Chapter:-One box slow lantern slide plates
(price is.), porcelain developing dish and developer.
A ITHERTO we have confined ourselves to the compara-
tively simple process of printing a visible image, by
- long exposure to daylight. We must now deal with
* a substance so sensitive as to be fully impressed with
a latent or invisible image by an exposure of one second to
daylight, or a proportionate time to artificial light.
The emulsion spread upon the plates we shall use for this
purpose, differs from that witli which the printing-out paper
(chap, i) is coated, in an essential feature. The emulsion
spread upon that paper contains gelatine, chloride of silver,
and free nitrate of silver. The plates we shall now use con-
tain only gelatine and chloride of silver, without the least
trace of nitrate. If any free nitrate of silver was present
the emulsion would be useless for development. Plates
that are made specially for development are prepared by
ruby or yellow light, and must never be exposed to white
light (no matter how feeble), except when we wish to im-
press them with an image.
The method of printing is briefly this: A negative is placed
(film upwards) in the printing frame, and a lantern plate is
placed upon it, film downwards, that is, both films in contact.
The back of the frame is then replaced and fastened.
The negative is then exposed to daylight for a second, or
to other illumination, as will be described.
Upon applying certain chemicals (known as the developer)
to the film of the lantern plate, after such exposure, the
latent image is converted into metallic silver, and becomes
visible in various degrees according to the action of light.
The image, so formed, is insoluble in the fixing bath (hypo),
but the other parts of the plate, i.e. those not altered by the
combined action of light and developer, still consist of
chloride of silver, which is easily soluble in the fixing bath.