If it is considered preferable to use the ordinary peroxide solution, then this must be used instead of water to make the gelatine solution, and the temperature must be kept as low as possible in melting it. It is, in fact, advisable to soak the gelatine for thirty minutes before melting. The dye solutions may be added in the same way as above, but probably the erythrosin will have to be increased to 30 to 40 ccm. This can be determined as before.

Instead of using the peroxide as sensitizer, either anethol or thiosinamin may be substituted. Anethol is the camphor obtained from aniseed oil, and has its characteristic smell. Thiosinamin is a colorless crystalline substance obtained from oil of mustard, and has but a faint garlic odor. A saturated solution should be made of the former in water and the paper bathed therein, or 10 drops of an alcoholic solution may be added to the gelatine. In the case of thiosinamin, one per cent may be added to the gelatine just before coating. In lieu of gelatine, collodion may be employed, about three per cent of pyroxylin in alcohol-ether (equal parts of each). The best method of working is to prepare the collodion as follows:

Pyroxylin 30 g.

Ether 500 ccm.

Alcohol 250 ccm.

Pour the alcohol on the cotton and when thoroughly soaked add the ether, and shake until dissolved. The dyes should then be dissolved in 250 ccm alcohol and added to the collodion, and finally ten drops of anethol. If the latter is obtained in crystals, then 0.5 g should be added to the alcoholic dye solution, or the same quantity of thiosinamin. Even more satisfactory results are obtained with the following dyes, the quantities being for 1000 ccm of collodion:

Primrose 1.5 g.

Victoria blue 0.4 g.

Curcumin crystals 1.66 g.

Auramin 0.34 g.

Curcumin is the coloring matter obtained from turmeric; if there is any difficulty in obtaining it, some powdered turmeric may be digested with alcohol for three or four days and then filtered; about ten per cent should be used. In this case the yellow solution must be added cautiously to the other dyes, testing occasionally on white paper, so that a neutral grey is obtained.

If the opal glass is to be used and the picture subsequently transferred, the glass should be coated with a 0.5 per cent solution of rubber in benzol; ordinary bicycle-tire cement may be used, thinned down to about one per cent. The gelatine is coated on the glass in the usual way, and alter exposure, washing, etc., the edges are cut round and the paper squeegeed down and stripped when dry.

To improve the stability of the dyes if anethol is used, the prints should be treated to successive baths of benzol, which dissolves this. If thiosinamin is used they must be treated with a weak nitrous acid bath, which can be made by adding about 10 drops of sulphuric acid to a five per cent solution of sodium nitrite, and then washed. Finally the prints should be treated with a ten per cent solution of tannin followed by a saturated solution of tartar emetic (antimony potassium tartrate), then rinsed and immersed in a saturated solution of lead acetate, washed and dried.

It is possible to prepare transparencies by this process, but as it requires three or four coatings or transfers, the game is not worth the candle, considering that so much better results can be obtained by other methods.