VARNISHING COLLODION PICTURES.
THE collodion picture, either positive or negative, will require to be varnished, to protect it from injury. I find that white lac varnish is the best for this purpose; the precaution necessary in using it is, that the plate should be gently warmed previously to pouring on the varnish, and after it is drained off, again warming the plate to assist in drying it quickly.
This varnish gives a hard and transparent coating to the picture, giving it great brilliancy and depth. If it is a negative drawing, it can be printed from in an hour after being varnished.
The best backing for positive pictures on glass, is a strip of cotton velvet, placed behind the picture in the case; this will be found preferable to either black varnish or paper, for the former is apt to penetrate and reduce the picture several tones, whilst the latter is seldom of sufficient depth to give the best effect to the positive image.
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