A Manual Of Photography

28 HISTORY OF PHOTOGRAPHY. Such was, in all its main features, the description given by Mr. Talbot in bis specification of his process for producing the Calotype, or beautiful picture (as the term signifies) : he in a second patent included the points stated in the next section. Section III.—Improvements in Calotype. Such is the term employed by Mr. Talbot, and these im- provements consist of the following particulars, constituting that gentleman's second claim. 1. Removing the yellowish tint which is occasioned by the iodide of silver, from the paper, by plunging it into a hot bath of hyposulphite of soda dissolved in ten times its weight of water, and heated nearly to the boiling point. The picture should remain in the bath about ten minutes, and be then washed in warm water and dried. Although this has been included by Mr. Talbot in bis specifi- cation, he has clearly no claim to it, since in February 1840 Sir John Herschel published, in bis Memoir " On the Chemical Action of the Rays of the Solar Spectrum," a process of fixing with the hot hyposulphite of soda. After undergoing the operation of fixing, the picture is placed upon a hot iron, and wax melted into the pores of the paper to increase its transparency. 2. The calotype paper is rendered more sensitive by placing a warm iron behind in the camera whilst the light is acting upon it. 3. The preparation of io-gallic paper, which is simply washing a sheet of iodized paper with gallic acid. In this state it will keep in a portfolio, and is rendered sensitive to light by washing it over with a solution of nitrate of silver. 4. Iodized paper is washed with a mixture of twenty-six parts of a saturated solution of gallic acid to one part of the solution of nitrate of silver ordinarily used. It can then be dried without fear of spoiling, may be kept a little time, and used without further preparation. 5. The improvement of photographic drawings by exposing them twice the usual time to the action of sunlight. The shadows are thus rendered too dark, and the lights are not sufficiently white. The drawing is then washed, and plunged into a bath of iodide of potassium, of the strength of 500 grains to each pint of water, and allowed to remain in it for one or two minutes, which makes the pictures brighter, and its lights assume a pale- yellow tint. After this, it is washed, and immersed in a hot bath