This section is from the book "The Druggist's General Receipt Book", by Henry Beasley. Also available from Amazon: The druggist's general receipt book.
Mr. HUGHES. - The description of glass known as "flatted crown" is well suited for positives, but before using it requires careful cleaning. The sharp edges should be first removed with a "corundum" file, or by drawing the sharp edge of one piece over the sharp edge of another; then place the glass on a clean flat surface, or put it in "a plate-cleaning holder," and pour a few drops of the plate-cleaning solution in the middle. Rub it carefully over every part with a bit of clean soft rag; turn the glass over, and do the other side the same. Then polish each side with a clean cloth, and finish with a soft chamois leather kept expressly for this purpose. Now, breathe on the glass, and if the breath deposits evenly the plate is clean. If the plate, however, shows patches and marks, it must be recleaned. Let the edges be carefully wiped, and the plate is ready for use.
The following preparation makes a good plate-cleaning solution for glasses that require mechanical friction to make them clean: - Ordinary water 5 oz., alcohol 5 oz., iodide of potassium 15 grs., iodine 3 grs. When dissolved add tripoli, prepared chalk, whiting, or rotten-stone, in sufficient quantity to make a creamy paste.
This thin pasty solution is to be rubbed on the plates on both surfaces and polished off as already described. This amount of cleaning will generally be sufficient for new glasses, but when they have been used they require more labour.
They must then be well washed under the tap, to get rid of all collodion and chemicals, and be wiped on cloths kept expressly for the purpose. Should the plates have been varnished they must be soaked for some hours in a saturated solution of washing soda till the varnish and film come freely off. The glasses must then be immersed for a few minutes in a solution composed of common nitric acid 2 oz., water 10 oz., and be well washed and treated as already described. It is a good plan when working, to have a dish of water at hand, and to place the spoilt pictures in it at once while they are wet, and at the end of the day to wash the glasses and put them away clean. By thus not allowing the films to dry on the glasses, they are much easier cleaned, and fewer failures will arise from dirty glasses.
Collodion is a good material for cleaning glasses when they are not very dirty. Pour a few drops on the glass and well rub it with a clean cloth, and you will entirely remove all grease; a hint may thus be taken how to use up waste collodion.
 
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