INTENSIFICATION Intensifier: 12 grams bichloride of mercury dissolved in 400 c.c. of water 15 " iodide of potassium " " 40 " " " 24 " hyposulphite of soda " " 60 " " " Or: 1/2 ounce bichloride of mercury dissolved in 20 ounces of wad 5 drachms iodide of potassium ,, It 2 " It It 1 ounce hyposulphite of soda ii di 3 II It " Dissolve separately and combine the first and second and then add the third. Slightly warming the water for the mercury saves time in dissolving it. Keep the solution in a wide mouthed, glass stoppered bottle. Great care should be exercised in mixing and storing this bath as the mercury is excessively poisonous. Never put the bare fingers in the solution but use rubber tips or gloves.
In practice the author uses the following method for dissolving the chemicals as in this manner a still stronger solution is obtained which acts almost instantaneously in local work: Place the dry mercury in a mortar and add to it a small quantity of water by estimation, say an ounce or about 30 c.c. or less. About 50 turns of the pestle saturates the water completely with the mercury when it is allowed to settle for a few seconds and the clear solution decanted off into the bottle. Repeat this operation as many times as is necessary to carry off all the mercury. Then rinse the mortar and dissolve the potassium all at once in a small quantity of water and pour it into the bottle with the mercury solution. On dissolving and adding the hypo in a similar manner the bath will become clear, with slight shaking, and is then ready to use. Do not use warm water for this method as the bath would be too strong to use success fully. For local work pour out only the neces sary amount of solution and after using it pour into a separate bottle and save for general work. This solution keeps well and for general intensi fication it can be used repeatedly until it begins to work too slowly when it should be thrown away. It may of course be weakened with water for general work if it is desired to slow its action. In this case, however, a little of the full strength solution should be saved in a separate bottle for use in local work.
Should a negative be unintentionally over intensified it may be again reduced by first washing it well in several changes of water and then placing in a strong, fresh solution of hypo and water. This work may also be done locally by applying the hypo solution with the regular reducing brushes or with absorbent cotton in the usual way. In fact the cotton may be used
instead of brushes for all this work but rubber finger tips or gloves should then be worn as has been stated. Or the tuft of cotton may be twirled on the end of a stick, as the spindle from a film roll with the metal ends removed. Three soft brushes of different sizes, one set for re ducing and another set for intensifying are, however, much preferable. The smallest should be a rather large ordinary "spotting" brush, the medium one an ordinary round quill handled camel's hair brush, and the largest should be a half inch or a one inch, rubber bound camel's hair brush.
Local intensification should be done on the stand with the strong solution, but a tray with weaker solution should be used for treating the negative throughout. The precautions in tech nique as mentioned in the section on reduction, such as refer to the excess of solution when treating small areas, etc., apply the same to intensification.
As the negatives are intensified they are re turned to the bath with the others and when all are finished they should be washed thoroughly and placed to dry. It is advisable to go over each negative with absorbent cotton just be fore placing to dry to take off any sediment which may be clinging to it. In the case of films the author has found in practice that ten changes of water given with not less than two minutes moving in each, is sufficient to wash them thoroughly.
The importance of any method of working cannot be judged logically until one has really made it a part of himself and when this method of treatment, which is performed in bright light and under conditions which give absolute freedom to the judgment, shall be recognized and used as a legitimate part of the process one takes on a feeling of freedom and power in the making of his negatives which cannot be expe rienced in any other way.
Negatives which are of historical importance should be duplicated or should have positives made from them by contact on plates or film, from which any number of negatives may later be made, also by contact. For reasons of permanency such positives and negatives should be brought to the desired opacity in the developer, or should be over-developed and then reduced, as the permanency of intensified emulsions is always a matter of doubt.