NEGATIVE PROCESS--SOLUBLE COTTON--PLAIN COLLODION--DEVELOPING
SOLUTION--RE-DEVELOPING SOLUTION--FIXING THE IMAGE--FINISHING THE
IMAGE--NITRATE OF SILVER BATH.
Negative Process.
The manipulations and chemicals employed in the production of the negative
collodion pictures are very similar to those already given for operating
by the positive process; frequent reference will therefore necessarily be
made to portions of that process, as described in the preceding pages,
and only such parts will be given here, as do not correspond with the
foregoing.
It is thought advisable to omit in this chapter every reference that
does not have a desired tendency to aid the operator in the plain
straightforward order of manipulation. The negative process is fast
becoming popular and needs the attention of all who desire to keep pace
with the experiments in the art. Since the first edition of this work it
has been my pleasure to see many fine photographic specimens produced by
the following process, and no one need fail, if he will carefully adhere
to the details given.
There perhaps may be circumstances making it advisable for some to
have but one nitrate of silver solution for both positive and negative
collodion pictures: for such, a process will be given in the following
pages, which has recently appeared in _Humphrey's Journal_, and is called,
after its author, the "Helio Process," this is well adapted for most
purposes.
Soluble Cotton.
The method for preparing this has been given in page 41. It is prepared in
the same manner for both positives and negatives.
Plain Collodion.
The preparation of plain collodion employed is the same as that described
at page 53.
Developing Solution for Negatives.
Rain or distilled water 6 ounces.
Protosulphate of iron 300 grains.
Acetic acid 2 ounces.
A little alcohol may be added to make it flow more evenly over the
plate--say 1 oz.
This solution can be kept in a pint bottle, and should have a funnel
devoted solely to the purpose of filtering it. One of the most convenient
dishes for receiving this solution, when poured over the plate, is a bowl
with a lip to it, as it can be readily poured back into the funnel.
The mode of employing this developer is the same as that for positives,
described at page 133. It may be used an indefinite number of times, but
should be kept clean; it soon assumes a red color.
Re-developing Solution.
This solution is for the purpose of giving increased intensity to the
negative, but as its use in the hands of beginners is attended with some
difficulty, I would not recommend the operator to try it until he has had
considerable experience in the developing process, or he will undoubtedly
spoil his proofs. Its use requires promptness of action and quick
observation.
The following is the formula for its preparation:
Water 4 ounces.
Protosulphite of iron 400 grains.
Put this into a bottle, and when the crystals are dissolved, it is ready
for use. It should be kept filtered, and can be used only once. Now in
another bottle put
Water 4 ounces.
Nitrate of silver 48 grains.
Remarks.--The impression is to be well washed after the developing
solution has been poured off, and then the _re-developing solution_ (that
portion containing the protosulphate of iron) can be poured on--the plate
being held perfectly level: the surface is completely covered; the water
containing the nitrate of silver should then be poured _rapidly_ on, to
mix with the iron, when the surface of the impression will instantly
commence to blacken; and if the action be allowed to continue for a
lengthened period, say one minute, the impression will be ruined.
It is a matter worthy of notice, that there is no perceptible action
when the iron solution is poured over the glass; but the action is very
energetic the instant the nitrate of silver solution comes in contact with
the iron salt and the silver.
As soon as any change can be observed, after the re-developer has been
poured over the plate, it should be _quickly_ and copiously washed off
with clean water, and then it is ready for the fixing process.
I would dissuade novices in the art from practising with the
_re-developing solution_, until they have first thoroughly mastered the
entire process of taking negatives. The developing solution is the only
one used by operators generally, and will, with proper care, produce
satisfactory results.
Fixing the Image.
Water 8 ounces.
Hyposulphite of soda 4 ounces.
Remarks.--This is nearly a saturated solution. The glass can be put in a
dish and the solution poured over, or held in the hand, in the same way
as the plate in the daguerreotype process. It can readily be seen when
a sufficient action has been attained, as the unaltered bromo-iodide of
silver will be dissolved, leaving only the reduced surface holding the
image.
This action should not be continued too long, as it affects the intensity
of the picture, injuring it for printing.
The glass should be well washed by pouring over it clean water, and then
it can be stood away to dry, in a _nearly_ perpendicular position, on
clean blotting paper, or otherwise, as is most convenient; when thoroughly
dry, it is ready for the finishing.
Finishing the Image.
This is done with the same material, and in the same manner, as that given
for positives--page 134.
Remarks.--The glass negatives, when not wanted for use, should be
carefully put aside in a box, and kept free from dust and dampness: by so
doing, it is believed that they will remain good for any length of time.
Nitrate of Silver Bath.
This solution differs only from the positive bath, by omitting the _nitric
acid_: in all other respects it is precisely the same, and is prepared by
the same formula, as given at page 64.
This is called the _neutral bath_, and is best adapted to the negative
process. The nitrate of silver employed in its preparation should be
perfectly free from excess of nitric acid, otherwise the whole solution
will be slightly acid.
If it should not be convenient to obtain nitrate of silver without this
objection, the acid may be neutralized by putting into the solution a
small quantity of common washing soda-- say 1 grain to each 100 grains of
nitrate of silver--previously dissolved in about half an ounce of water.
This may be put in at the same time that the iodide of potassium is, and
it would save one filtration.
In twenty samples of nitrate of silver that I have tried the above
quantity of soda has been found sufficient; if, however, the _white_
precipitate first formed is re-dissolved on shaking the mixture, free
nitric acid is present, and more of the soda may be added.
This bath will improve by age, and be less liable to fog after having been
in constant use for one or two weeks.
Operators who have the means, and design following the art professionally,
will find it to their advantage to make from two to three times the
quantity of solution they require for immediate use: by this means
they will be enabled to replenish their stock, which may be used up or
otherwise lost.
PRACTICAL DETAILS
OF THE
=PRINTING PROCESS.=