Collodion, Photograph′ic

1. There are so many methods adopted for preparing photographic collodion, that a large volume might be filled with notices of them. We have retained Mr Hardwich’s forms, which were formerly much esteemed by practical photographers, and appended to them modern formulæ which are now, we believe, in much greater demand, and for which we are indebted to Mr Ernest Spon’s valuable book ‘Workshop Receipts.’ 2. Pyroxylin, and iodide of cadmium, or ammonium, of each 15 gr.; ether, 3 1 ⁄ 2 oz.; alcohol, 1 1 ⁄ 2 oz. Place the two first in a dry bottle, then pour on the spirits of wine, shake the mixture well, then add the ether, shake again and let it stand for 12 hours. Decant the clear portion into a wide-mouthed bottle, keep well stoppered, and in the dark. Avoid shaking the bottle when about to use the collodion, and never quite use all the bottle contains, as the sediment which will accumulate at the bottom would spoil the picture. The preparation of a sensitive collodion, whether positive or negative, includes three distinct operations, namely, the formation of the pyroxylin or gun-cotton, the conversion of this into plain collodion, and the final proce of iodising the collodion.