RE: "serum of milk"
Email trouble here means this probably won't arrive for a week, but in case you're still interested... A Dictionary of Photography, Thomas Sutton, c. 1858: SERUM of MILK. Serum, or whey, is the watery liquid which remains after the cream and cheese have been removed from milk. It contains a sugar called sugar of milk and some soluble salts, also a small quantity of uncoagulated casein. It is of great use in photographic printing upon plain paper for giving surface vigour to the proofs without any disagreeable glazed appearance; - and in the paper negative process it seems to act better than any other substance in giving density to the blacks, probably from the presence of the salts of lactic acid which it contains. The simplest and best mode of making whey for the paper processes is to add lemon juice to skimmed milk in the proportion of about 2 spoonsful of lemon juice to a quart of whey. Boil them together and strain the liquid through a cloth, which separates it from the curd. It should be of a greenish colour and slightly opalescent. About 6 grains of salt may then be added for a positive printing paper and about 5 grains of salt and 10 of iodide of potassium for negative paper. The acidity of the whey thus prepared preserves the whites of the paper beautifully. Whey may be made by adding a piece of rennet about 3 inches square to a quart of skimmed milk, and putting it in a bason on a hob so as to raise the temperature to about 120 degrees. In half an hour or so the curd is formed. This is called sweet whey, from its being not so acid as the other. It contains rather more casein. So, it just remains to find out what a 'bason' is. Liam
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