This section is from the book "Modern Photography In Theory And Practice", by By Henry G. Abbott. Also available from Amazon: Modern photography in theory and practice: A hand book for the amateur.
Even the professional, who has had years of experience, does not produce a perfect plate every time, and the amateur must not be discouraged if he meets with failures very often. The professional resorts to many different dodges for doctering up his unsatisfactory negatives. The most common faults with amateur negatives are that they are either too thin or too dense, i. e., they are either under or over exposed or developed, or both. To a certain extent these evils can be remedied. If our negative is too thin and gives a flat print with little relief of light and shade, we may improve it by means of intensification. If the negative has been dried it must be soaked in water for about twenty minutes before applying the intensifier. If the negative is not yet dried, it must be very thoroughly washed to remove the very last traces of hypo.
Bi-Chloride of Mercury........31 grs.
Distilled Water................ 4 oz.
Sulphite of Soda, Crystals..............154 grs.
Distilled Water................ 3 oz.
The negative is laid in a tray and solution No. I is poured over it. The tray must be kept rocking constantly as in developing and see that the solution thoroughly covers the entire plate or you will have streaks.
It will soon begin to turn a dirty white and the length of time it is to remain in the solution depends largely on the amount of intensification desired. The negative is removed and rinsed for a few minutes in running water and then put in another tray and solution No. 2 is poured over it. Special trays should be provided for intensification and so labeled and not used for other purposes, unless they are made of glass or porcelain, and then they must be thoroughly cleaned after use. As soon as solution No. 2 begins to turn the plate black, remove it and look through the negative towards the light and when it has blackened sufficiently remove it from the solution and wash for at least one hour in running water and then put it away to dry.
Chloride as well as Bi-Chloride of mercury is used as an intensifier and the following is a standard formula:
Chloride of Mercury..........1oo grs.
Ammonium Chloride...........100 grs.
Distilled Water............... 10 oz.
Sodium Sulphite................. 1 oz.
Distilled Water.................16 oz.
In making No. 1, dissolve the ammonium chloride in the water and then add the chloride of mercury. Shake the bottle occasionally and when the mercury is all dissolved it is ready for use. The solution acts very much like that previously described. When the plate has turned white it should be lifted out, washed for about twenty minutes and then treated with No. 2 until it turns black and the color is sufficiently dense. Should a very dense intensification be desired a 5 per cent solution of ammonia may be substituted for the sulphite.
An Indian Ruin. S, Narrayen Rao, Bangalore, India.
The Cramer Dry Plate Works advise the following:
Bi-Chloride of Mercury, Saturrated Solution................ *q. s.
Iodide of Potassium...........1 1/4 oz.
Distilled Water................ 6 oz.
Hyposulphite of Soda.......... 1 oz.
Distilled Water.................20 oz.
In solution No. 1 a saturated solution of the mercury should be made with water, and this should be poured gradually into the solution of potassium and water until the point is reached, when the red precipitate will no longer dissolve by shaking, but be careful not to add more mercury than just enough to make the solution very slightly turbid. You are now ready to add No. 2. You will note this is a single solution intensifier. For use, the above solution should be diluted with about three parts of water. Proceed as with other intensifiers until sufficient intensity is reached and wash thoroughly. Should the plate be over intensified it may be reduced by placing it in the hypo fixing bath for a short time.
Be careful to mark all bottles containing intensifiers Poison and put them away carefully.
Do not try to intensify plates when you have scratches or cuts on your fingers and do not place your face over the solution where you would inhale the fumes of the mercury. Keep your fingers out of all mercury baths as much as possible.
*q. s. signifies a sufficient quantity.
Mr.John Carbutt recommends the following:
Bichlor. Mercury............. 240 grs.
Chloride Ammonia............240 grs.
Distilled Water................ 20 oz.
Chloride Ammonia............240 grs.
Water......................... 20 oz.
Distilled Water................. 6 oz.
Cyanide Potass, C. P..........60 grs.
Distilled Water................. 2 oz.
Nitrate of Silver................60 gr.
Pour the silver into the cyanide solution while stirring. Let the plate to be intensified, wash for at least half an hour, then lay in a 5 per cent solution of alum for ten minutes and again wash thoroughly; this is to insure the perfect elimination of the hypo. The least trace of yellowness after intensifying shows that the washing was not sufficient.
Flow sufficient of No. 1 over the negative to cover it and allow to either partially or entirely whiten; the longer it is allowed to act, the more intense will be the result; pour off into the sink, then flow over No. 2 and allow to act one minute; wash off, and pour over, or immerse in No. 3 until changed entirely to a dark brown or black. No. 3 can be returned to its bottle, but Nos. 1 and 2 had better be thrown away. Wash thoroughly and dry.
We do not recommend the mercury intensifiers and advise amateurs to have as little as possible to do with mercury in any form. Even with the most thorough washing you will sometimes fail to eradicate the mercury entirely, and after a while you will find your negative ruined. The Uranium intensifier gives as good if not better results and without any danger of destroying the ate.