| WATER COLORS WHICH RESIST THE ACTION OF LIGHT. | ||||
|---|---|---|---|---|
| Red. | Indian red. | Light red. | ||
| Orange. | Mars yellow. | |||
| Blue. | Cobalt blue. | French blue. | Smalt. | New blue. |
| Brown. | Raw umber. | Burnt sienna. | ||
| Green | Terre verte. | |||
| Yellow. | Cadmium yellow. | Yellow ochre. | Roman ochre. | |
APPENDIX.
Although we intended to only describe the printing processes without the use of silver salts, we thought it would be well to complete this work by giving the most practical and interesting processes ever published to obtain permanent photographs; as they may give rise in the hand of experimenters to useful applications.
From time to time processes are published under “queer” names, which are based on the well known actions of reagents on the ferric salts reduced by light. They are derived from those described in the following pages.
We call specially the attention of the reader to the process of Poitevin, by which one can experiment with every ferric salts, citrate, lactate, oxalate, tartrate, benzoate, etc., by simply exciting with the corresponding acid. Observe that to obtain good results the paper should be strongly sized; it is a sine qua non, although not recommended by Poitevin.
C.J. BURNETT'S PROCESS(1857).
“A capital process for many purposes,” says Mr. Burnett, “is to float or steep the paper in a mixed solution of bichromate of potash and sulphate of copper, as for Hunt's chromotype process.[36] I have mixed gelatine, or occasionally grape sugar, or both with the solution;[37] but instead of developing it with nitrate of silver, as in chromotype, wash out the salt unaltered by light, and develop by floating on a solution of ferrocyanate of potassium. The purple red color of the copper salt which now forms the picture may be modified or changed [pg 110] in many ways,[38] viz., by soaking the picture, after the ferrocyanate of potassium has been washed out of the lights, in a solution of sulphate of iron. Solutions of gallic acid, tannic acid with alkalies of carbonate, may also be employed to modify or change the color. This process has the advantage that one may regulate the exact tone (black or useful neutral tint) to the greatest nicety by the time we allow the print to remain in the iron toning bath.”