CALOTYPE is the name given by Mr.
Fox Talbot to his improved Photo graphic method. The method of obtain ing Calotype pictures is as follows :—Take a sheet of the best writing paper. Dis solve 100 grains of crystallized nitrate of silver in 6 ounces of distilled water. Wash the paper with this solution, with a soft brush, on one side, andput a mark on that side, whereby to know it again. Dry the paper cautiously by a distant fire, or else let it dry spontaneously in a dark room. When or nearly so, dip it into a solution of iodine of potassium, of 500 grains to a pint of distilled water, and let it stay two or three Minutes in this solution. Then dip it into of water, dry it lightly with blottihg pa per, and finish drying it at a fire, or spon taneously. All this is best done by candlelight. The paper so prepared the author ealls iodized paper. It is scarcely sensitive to light ; nevertheless it ought to be kept protected from the light. Shortly before this paper is wanted for use, wash a sheet of it with this liquid: Dissolve 100 grs. of crystallized nitrate of silver in 2 oz. of distilled water ; add one sixth of its volume of strong acetic acid : let this mixture . be called A. Make a saturated solution of crystallized gale acid in cold distilled water ; the quanti ty dissolved is very small ; call this so lution B. When a sheet of paper is wanted for nse, mix together the liquids A and B in equal volnmes,,but only mix a small quantity of them at a time, he cause the mixture will not, keep long without spoiling ; call this mixture the gallo-nitrate of silver. With wash the iodized paper on the marked , side, by candlelight. Let the paper rest half a minute, and then dip it into water, , Then dry it lightly with paper, and at a distance from the fire. The author has named the paper thus prepared Calotype paper, on account of its great utility in obtaining the pictures of objects with the camera. obscura. If this paper be kept in a press, it will often. retain its quali i ties n perfection for three months or more, being ready for. use at any mo ment • but this is not uniformly the ease.
It is best used a few hours after it. has been prepared. . The Galotype paper is sensitive to light in an extraordinary degree, which transcends a . hundred times or more that of kind of photo ; it will take an impression from sample moonlight not concentrated by a lens.
Use of the Paper.—Take a piece of this paper, and having covered of it, expose the other half to daylight for the space of one second in dark cloudy weather in winter, when there will be a strong impression upon the paper, but latent and invisible, and its existence not to be suspected by any one. To make it visible wash the paper once more with the gallo-nitrate of silver, and then warm it gently before the lire. In a few se conds, the part of the paper upon which the light has acted begins to darken, and finally grows entirely black, while the other part of the paper retains its white ness. This paper is well suited to re ceive images in the camera, obscura. When the aperture of the lens amounts to one third of the focal length, and the object is very white, as a plaster bust, &c., one second is sufficient_ to obtain a pretty good image of it, made visible by washing and warming.
The Fixing Proeess.—First wash the picture with water, then lightly dry it with blotting-paper, and next wash it with a solution of bromide of potassium, containing 100 grains of that salt dis solved in eight or ten ounces of distilled' water. After a minute or two it should be again dipped in water, and then finally dried. The picture is in this manner, very strongly fixed ; and with this great advantage, that it remains transparent, and that, therefore, there is no difficulty in obtaining a copy of it. The Calotype picture is a negative one, in which the lights of nature are represented by shades ; but the copies are positive, hav ing the lights conformable to nature. A. negative calotype May serve to furnish' several positive ones,:but after a while it grows faint ; but it may be restored by washing by candlelight with gallo-nitrate of silver, and warming. A second series May now be taken.