Keep near at hand in a 64 oz. bottle this solution:
| Protosulphate of iron | 2 oz. |
| Citric acid | 1 |
| Water | 64 |
and in a small bottle a ten-grain-to-the-ounce solution of silver nitrate.
When a negative is to be strengthened, from the large bottle take enough of the solution to cover the surface; to this add a half dram of the silver and flow it over the negative.
A change of color will at once take place in the film, which will become darker as the silver deposit becomes heavier; if one application is not enough to secure the required density, wash the plate and proceed again, as before. p37
Negatives may be strengthened before fixing, if it is found necessary, by flowing the surface with the weak silver solution and afterwards using the ordinary developer.
When one has become accustomed to the work, and can tell that the negative is not dense enough before fixing, it is the best plan to re-develop before fixing.
The mercurial intensifying solution for dry plates is very nice for wet plates.
Having described the positive and negative collodion process, there remains to give an account of the latest and greatest achievement in photographic progress.