Found in Humphrey’s American Hand Book of the Daguerreotype.
Does it work? Has it ever been attempted? There’s no mention of red light, just heat/darkness.
Sounds too good to be true…
DAGUERREOTYPES WITHOUT MERCURY.
The following process possesses some interest, and is
worthy a trial from operators. M. Natterer, of Vienna,
discovered a process for obtaining proofs on iodized plates
with the chloride of sulphur, without the use of mercury.
A plate of silver is iodized in the usual manner, and then placed
on the top of a vessel six or eight inches high, having at
the bottom, in a small cup, a few drops of chloride of sulphur;
it should remain exposed to the action of the vapor until
the sombre yellow color is changed to a red, after which it
is brought to a focus m the camera, where it is exposed
to the light in the camera, for about the time necessary
to produce an ordinary daguerreotype. The plate is then taken
out and examined in the camera by the light of a candle.
It often occurs that no trace of the image is as yet perceptible,
but if the plate is heated by placing over a spirit lamp
the unprepared side, or if left for some time in the dark,
or, lastly, if exposed only a few seconds to a weak, dimmed light,
the positive picture then appears with all its shades.
Of these three modes of bringing out the image, the second
is superior to the others.