Distilled water 10 oz.
Pyrogallic acid 6 grs.
Formic acid 1 oz.
The latter is not to be the concentrated acid, but merely the commercial
strength. These, when mixed, form so powerful a developing agent, that
the picture is brought out in its full intensity, almost instantly,
while at the same time all the deep shades are quite unaffected, and the
half-tones come out with a brilliancy I have never seen before.