Such is the term employed by Mr. Talbot, and these improvements 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 his specification, he has clearly no claim to it, since, in February 1840, Sir John Herschel published, in his 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 of hyposulphite of soda until the pale-yellow tint is removed, and the lights remain quite white. The pictures thus finished have a pleasing and peculiar effect.
6. The appearance of photographic pictures is improved by waxing them, and placing white or coloured paper behind them.
7. Enlarged copies of daguerreotypes and calotypes can be obtained by throwing magnified images of them, by means of lenses, upon calotype paper.
8. Photographic printing. A few pages of letterpress are printed on one side only of a sheet of paper, which is waxed if thought necessary, and the letters are cut out and sorted ; then, in order to compose a new page, a sheet of white paper is ruled with straight lines, and the words are formed by cementing the separate letters in their proper order along the lines. A negative photographic copy is then taken, having white letters on a black ground; this is fixed, and any number of positive copies can be obtained. Another method proposed by the patentee is to take a copy by the camera obscura from large letters painted on a white board.
9. Photographic publication. This claim of the patentee consists in making, first, good negative drawings on papers prepared with salt and ammonio-nitrate of silver; secondly, fixing them by the process above described; thirdly, the formation of positive drawings from the negative copy, and fixing.
These claims, taken from the specification as published in the Repertory of Patent Inventions, are preserved, in their original form, for the purpose of showing how much that is now fully accomplished was foreseen by Mr. Talbot as the result of his discoveries.