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 sensitive portions of the plate, and made to appear only by subsequent exposure to mercury, being equivalent to solarization.
There has been little said by our professors upon the subject of the position of the plates while exposed to the mercurial vapour.

Mr.
Hunt, in referring to this subject, says: "Daguerre himself laid much stress upon the necessity of exposing the plate to the mercury at an angle of about 45 deg..

This, perhaps, is the most convenient position as it enables the operator to view the plate distinctly, and watch the development of the design; but beyond this, I am satisfied there exists no real necessity for angular position.

Both horizontally and vertically, I have often produced equally effective Daguerreotypes." I presume from the last sentence of Mr.Hunt, that he has confined his experiments to the smaller sized plates.