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.