3 ounces of fresh white lac are dissolved in 1 pint of strong alcohol, and after filtering or decanting, as much water is added as it will bear without precipitating the lac; 1 ounce of good gelatine is soaked and dissolved in the pint of boiling water, and the lac solution is added with frequent stirring. If, at any stage of this operation, the gelatine is precipitated, a little more hot water must be added. The pint of lac solution ought, however, to be emulsified in the gelatine solution.
To use the emulsion, it is warmed, and the paper immersed in or floated on it for three minutes. When dry, the coated surface is floated in the following for a couple of minutes:—
| Ammonium chloride | 10 | grains |
| [28]Magnesium lactate | 10 | " |
When dry, it is sensitized on a moderately strong bath (that given on the last page will answer).
If more vigour in the resulting prints be required, it is floated on:—
| Citric acid | 5 | grains |
| White sugar | 5 | " |
This last bath improves by use, probably by the accumulation of silver nitrate from the sensitized paper.
Any of the toning baths given in [Chapter XII.] will answer, though Mr. Cooper recommends:—
| Solution of gold tri-chloride (1 gr. to 1 dr. of water) | 2 | dr. |
| Pure precipitated chalk | a pinch | |
| Hot water | 10 | ounces |
2 dr. of sodium acetate are to be placed in the stock-bottle, and the above solution filtered on to it. This is made up to 20 ounces, and is fit for use in a few hours; but it improves by keeping.