This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Warm water..................... , .......
Bichloride of Mercury.....................
Dissolving The Mercury. The bichloride of mercury will dissolve very slowly, but by persistent shaking most of it will dissolve. If particles remain undissolved use only the clear solution, as one of these small particles coming in contact with the negative is apt to leave an opaque spot.
( Or if by weight)
Sulphite of Soda - Anhydrous
The exact strength of clearing bath is not essential. Therefore, for convenience you may use your regular Sulphite Soda Stock Solution used for developing, and dilute it one-half by adding an equal amount of water.
Preparing The Plate To Receive The Intensifier. To intensify proceed as follows: First, place your plate, or plates, in running water for at least ten minutes, soaking the film thoroughly so that the chemicals will effect all portions evenly when applied. Use a tray just large enough to hold your plate, one that has not been used for any other chemicals. While your plates are soaking in the water place three ounces of your intensifying stock solution in your graduate, being careful that your graduate is perfectly clean, as the least bit of alkali or pyro would spoil the bath, and render it useless. Add to this mercury four ounces of water. Mix this solution thoroughly before you pour it into your tray.
138. By this time your plates have become thoroughly saturated with water. Pour off the water, and pour on your intensifying solution. Keep the solution flowing over the plate by rocking the tray until the surface becomes perfectly white. Occasionally examine the plate by looking through it to the light. When the plate appears dense and the surface is quite white, and in your judgment the plate has been intensified far enough - taking into consideration that the plate will lose some of its density in the clearing bath - then rinse it carefully in clear water for a few moments, and place the plate in the tray containing sulphite of soda clearing solution. Rock the tray constantly, allowing the plate to remain in the sulphite until it has returned to its original color.
Re-Intensifying. If you find after clearing that the plate does not contain the desired strength, repeat the operation, but before doing so wash carefully, thoroughly eliminating the sulphite of soda so that you will carry no sulphite into the intensifying solution. This operation of intensifying can be repeated two or three times, and each time the negative will gain in strength. After the plate is sufficiently intensified and cleared, place in running water for not less than ten minutes, or until it is thoroughly washed, and then place in the rack to dry.
When To Stop Action Of Intensifier. The greatest difficulty in intensifying plates is to know when to stop. This can only be determined by careful observation, watching the plate carefully, examining the surface and color of density while the mercury is bleaching the plate, and carefully noting how much strength it is losing in the clearing bath. If the reader will observe, and make mental notes of the different results obtained, he will soon be able to judge by looking through the plate just how far to carry the intensifying. If the plate has not been carried far enough, as stated above, repeat the operation, paying close attention to its appearance in each condition, so that you may be able to judge your future results upon the first application.