For various reasons I prefer a high temperature and short exposure.
It accelerates the process. It renders the lights of the picture
more strong and clear, while the deep shades are more intense.
It gives a finer lustre to the drapery. The solarized
portions also are very seldom blue, especially after gilding.
If heated too high, however, the light parts become of a dead,
chalky white, and the shadows are injured by numerous little
globules of mercury deposited over them. Just the right
quantity of mercury leaves the impression of a transparent,
pearly white tone, which improves in the highest degree in gilding.
To mercurialize with exactness is a nice point. If there
is reason to suspect having timed rather short in the camera,
reduce the time over mercury in a corresponding proportion.
A dark impression will be ruined by the quantity of mercury
which would only improve a light one.

If practicable, it is most expedient that the plate be submitted
to the action of mercury immediately on coming from the camera.
I have frequently, however, carried plates for miles
in the plate-holders and after exposing in the camera,
brought them back to expose to mercury, and obtained fair proofs;
but for the reason before given, it is advisable to carry
along the bath, and bring out the impression on the spot.

It is sometimes the practice of inexperienced operators to take
the plate off the bath and examine the impression by solar light.
This plan should be abandoned, as it is almost sure to produce
a dense blue film over the shadows.

This I am led to believe is occasioned by the action of light on the yet