The film, after dipping in the Bath, should appear opalescent and not too yellow and creamy. Pale-blue films yield very good Positives, but with more liability to failure than thicker films ([p. 109]).
If the Positives are not perfectly clear and transparent in the shadows, dissolve 5 grains of Iodine in an ounce of Spirits of Wine (not methylated), and add a few drops until the Collodion assumes a golden-yellow colour.
In hot weather advantage will be gained by somewhat increasing the quantity of Alcohol in Collodion; the evaporation of the solvents being retarded, and the film rendered less liable to become dry before development. Anhydrous Alcohol of Sp. Gr. ·796, may be mixed with pure Ether of ·715, even to the extent of equal parts; but this is the extreme limit, and with the strongest spirit ordinarily obtainable, the Collodion will often become somewhat glutinous if the proportions (by measure) of 5 parts of Ether to 3 of Alcohol be exceeded.
Collodion prepared by Formula No. 1, and iodized with Iodide of Cadmium, may be kept for weeks or months without much loss of sensitiveness; but when Alkaline Iodides are employed as in the second Formula, Iodine is liberated, and the fluid becomes at last brown and insensitive.
THE NITRATE BATH.
| Nitrate of Silver | 30 | grains. |
| Nitric Acid 1/20 minim, or Acetic Acid (glacial) | 1/6 | minim. |
| Alcohol | 15 | minims. |
| Distilled water | 1 | fluid ounce. |
Nitrate of Silver which has been melted, in order to expel Oxides of Nitrogen, is always the most certain in its action: but the heat must not be raised too high or the salt will be contaminated with Nitrite of Silver.
In the Vocabulary (see Part III.) directions are given for the preparation and purification of Nitrate of Silver; also for the testing of distilled water, and the best substitutes when it cannot be obtained.
The Bath must be saturated with Iodide of Silver, and Nitric Acid neutralized if it be present. Nitrate of Silver however which has undergone fusion is free from Nitric Acid.