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Cj 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 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."

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