No. 1.
Neutral oxalate of potash 1 lb.
Water 5 pints.
Acidify with oxalic acid and filter.
No. 2.
Protosulphate of iron 1 lb.
Water 2 quarts.
Filter and add 60 drops sulphuric acid.
No. 3.
Bromide of Ammonium 1 oz.
Water 10 oz.
The developer is prepared by mixing together in a [p059] graduate
the quantity necessary to cover the plate in the following
proportions:
Oxalate solution 3 parts.
Iron solution 1 part.
Bromide solution 1/8 part.
For instance, it will take about 8 ounces to cover an 8x10 plate in
a flat dish; to make this quantity take of the
Oxalate 6 oz.
Iron 2 oz.
Bromide 2 drs.
Always pour the iron into the oxalate solution, then add the
bromide, and having placed the exposed plate in the dish pour the
developer upon it, covering the surface of the plate as quickly as
possible and removing any air bells that may stick to the surface.
Keep the solution in motion on the surface of the plate and in a
short time the image will begin to appear, the high lights first,
then the intermediate shades, last of all detail will be seen in the
shadows. Now pour the developer off, take the plate out of the tray
and look at the back of it. If the subject or image can be
distinctly seen it may be considered finished and only needs to be
washed and fixed.
If the plate has been over-exposed, which will be indicated by the
image appearing quickly, wash off the developer with water, add more
bromide to the solution and immerse the plate again.
If, on the contrary, the plate has not had enough time, it will be
indicated by developing very slowly and with a very thin and weak
image; when such is the case add more of the iron solution, however,
not more than to make the proportion of the iron nearly [p060]
one-fourth of the whole solution. More than this proportion will
cause a yellow precipitate, which will settle on the surface of the
film and destroy it. If by this course you succeed in securing
sufficient detail in the shadows, the negative may afterwards be
strengthened.
It is as well, however, when a plate is found to be undertimed (and
it is possible to make another from the same subject) to throw it
away; it will scarcely repay further attention.
It will be seen that a considerable margin in time of exposure can
be allowed and provided for. Yet none the less it is of the utmost
importance to learn to give the correct and proper exposure to
secure the finest results.
This, it is true, is not always possible, and as an under-exposed
plate is lost, any error in exposure would better be in too much
rather than in too little time.
It is said by some that by the use of citrate of soda almost any
degree of over-exposure may be remedied, but there remains the fact
that for a restraining agent to be of any value its application to a
negative in development must be almost instantaneous upon the
earliest discovery of the over-exposure.
When a large number of plates have been exposed and the first
developed indicates that all have been overtimed, then a 50 per
cent. solution of citrate of soda, used with judgment, might result
in saving the lot.
When over-timing makes itself visible unexpectedly and it is feared
that the development will have proceeded too far before the retarder
can act, a good plan is to take the plate out of the dish and flow
over it a solution of citric acid, containing a little chrome alum,
[p061] which will immediately stop the action of the developer and
give time to make other arrangements.