Alkaline Toning.—Owing to the bleaching action which occurs in toning silver prints with gold, which is slightly acid, certain experiments were made, and it was found that bleaching increased in proportion to the quantity of hydrochloric acid added. Now, in the action of toning chlorine is disengaged, and in order to render this powerful bleaching agent inert it has been proposed to introduce a substance capable of combining with it, and thus, in absorbing it, prevent undue loss of vigor. To obtain this a slightly alkaline toning bath became a necessity, and to Mr. Waterhouse we are indebted for the introduction of the alkaline salts (Hardwich).
Here is an example:
Experiment 4.
| Sodium carbonate (Na2HCO3) | 5 | grains. |
| Auric terchloride (AuCl3) | 1 | grain. |
| Water | 10 | ounces. |
Instead of the dry bicarbonate we will use a saturated solution. In this as well as the following experiments we shall tone three prints of the same subject, viz., ordinary, fumed, and preserved.
Mr. Maxwell Lyte has written on and investigated the properties of toning solutions a great deal more than most men, and we find the following emanating from Mr. Lyte:
| Sesquichloride of gold | 15 | grains. |
| Phosphate of soda | 300 | " |
| Distilled water | 1¾ | pints. |
And in the same communication it is mentioned that 180 grains of borax may be substituted for the phosphate with a like result. Therefore it will be seen that a borax toning bath is not of recent discovery, although it does not appear to have been quoted in many formulæ for at least a dozen years after its publication.
After the publication of Mr. Lyte's formulæ it was found that other salts behaved similarly; and among the first suggested we found sodium acetate, the qualities of which, extolled by the introducer, Mr. Hannaford, have since been verified by the whole photographic world. Here is one of the ordinary formulæ:
Experiment 5.