A Few Technical Hints
A Few Technical Hints
EMULSIFYING. - I have found no method of emulsification so good as that recommended by Mr. W. K. Burton, but not, I believe, originated by him. This process consists in dropping the nitrate of silver in crystals into the bromide solution and shaking until the crystals are entirely dissolved. The emulsion thus formed will always be found to be ruby red by transmitted light.
BOILING. - The common notion, that the length of time during which emulsion may be boiled with advantage is limited to about thirty minutes, is a complete mistake. If the solutions be made slightly acid, as recommended by the Editor of the ALMANAC, and if there be a small amount of iodide in the emulsion, as advised by Captain Abney, boiling may be continued with advantage for one or even two hours, especially if the emulsion be in a not too concentrated form.
WASHING. - If an emulsion which is in a fine state of division be washed only for a few minutes, but during that time be kept in constant motion, it is more thoroughly purified from the soluble bromide, iodide, and nitrates than could possibly have been accomplished by a long period of soaking without movement or in a coarse state of division. The emulsion, too, is liable to be deteriorated by a prolonged soaking.
COATING THE PLATES. - the plates should be thickly coated — at least so thickly that the form of the dark room lamp flame cannot he distinguished through the film when it is wet. The advantages of a thick film are as well known as they are enormous, if the emulsion be of good quality. If, however, it be defective all defects will be increased by the thickness of the film. Thus, fogs — whether chemical, green, red, yellow, or otherwise — will show in a ratio which is directly proportionate to this thickness.
DRYING. — In drying, the great object aimed at should be to obtain a thoroughly-brisk current of air well distributed among the plates. If this be secured and the drying-box placed in a perfectly dry spot there is no need for artificial heat, even in winter. Plates so dried — that is, with an ample current of air at atmospheric temperature — never frill, unless the gelatine from which they have been made has been absolutely rotten.
FRILLING. — Frilling of the most obstinate character — even such as makes its appearance in the developing solution — may be prevented by mixing the developer with a certain amount of methylated spirit. Rinse the plate afterwards with a small quantity of methylated spirit and water, and place it in a mixture of a saturated solution of chrome alum and methylated spirit. The quantity of methylated spirit in all these solutions may vary from ten to twenty-five per cent., according to the obstinacy of the malady. With the latter quantity development will he greatly protracted.