CAMEO 675 



Then dip the paper into a vessel of water, dry it lightly with blotting-paper, and finish 

 drying it at a fire, which will not injure it even if held pretty near ; or else it may be 

 left to dry spontaneously. All this is best done in the evening by candle-light : the 

 paper, so far prepared, is called iodised paper, because it has a uniform pale-yellow 

 coating of iodide of silver. It is scarcely sensitive to light, but nevertheless it ought 

 to be kept in a portfolio or drawer until wanted for use. It may be kept for some 

 considerable time without undergoing change, if protected from sunshine. When the 

 paper is required for use, take a sheet of it, and -wash it with a liquid prepared in the 

 following manner : 



Dissolve 100 grains of crystallised nitrate of silver in two ounces of distilled water ; 

 add to this solution one-sixth of its volume of strong acetic acid. Let this be called 

 mixture A. 



Make a saturated solution of crystallised gallic acid in cold distilled water. The 

 quantity dissolved is very small. Call this solution B. 



Mix together the liquids A and B in equal volumes, but only a small quantity of 

 them at a time, because the mixture does not keep long without spoiling. This mix- 

 ture Mr. Talbot calls the gallo-nitrate of silver. This solution must be washed over 

 the iodised paper on the side marked, and being allowed to remain upon it for half a 

 minute, it must be dipped into water, and then lightly dried with blotting-paper. This 

 operation in particular requires the total exclusion of daylight ; and although the paper 

 thus prepared has been found to keep for two or three months, it is advisable to use 

 it within a few hours, as it is often rendered useless by spontaneous change in the dark. 



Paper thus prepared is exquisitely sensitive to light ; an exposure of less than a 

 second to diffused daylight being quite sufficient to set up the process of change. If a 

 piece of this paper is partly covered, and the other portion exposed to daylight for the 

 briefest possible period of time, a very decided impression will be made. This impres- 

 sion is latent and invisible. If, however, the paper be placed aside in the dark, it will 

 gradually develop itself; or it may be brought out immediately by being washed over 

 with the gallo-nitrate of silver, and held at a short distance from the fire, by which 

 the exposed portions become brown, the covered parts remaining of their original colour. 

 The pictures being thus procured, are to be fixed by washing in clean water, and 

 lightly drying between blotting-paper, after which they are to be washed over with a 

 solution of bromide of potassium, containing 100 grains of that salt, dissolved in eight 

 or ten ounces of water ; after a minute or two, it is again to be dipped into water, and 

 then finally dried. The Collodion process has almost entirely superseded the Calotype. 

 See COLLODION and PHOTOGBAPHT. 



CAXiUMBA. See COLOMJU. 



c AMBAY STONE. A variety of carnelian imported from the East Indies. 



CAZVXBOCXA. See GAMBOGE. 



CAMBRIC. (Batiste, Fr.; Kammertuch, Ger.) A sort of very fine and rather 

 thin linen fabric, first made at Cambray. An excellent imitation of it is made in 

 Lancashire and in Scotland, woven from fine cotton yarn, hard twisted. Linen cambric 

 of a good quality is also now manufactured in the United Kingdom from power-spun 

 flax ; this is frequently called Cambric muslin. 



CAMBXiSON IVXUVERAZi. See CHAMCELEON MINERAL. 



CAMEO. (Camee, Fr. ; Cammeo, It.) Correctly a precious stone engraved in 

 relief, as opposed to an intaglio, which is cut into the stone. The earliest cameos 

 appear to have been cut upon the onyx, and subsequently, on the agate. The true 

 cameo is formed upon a stone having two or more layers, differing in colour ; and the 

 art of the cameo-engraver consists in so cutting as to appropriate those differently 

 coloured layers to distinct parts or elevations of the work. 



Many of the varieties of chalcedony present in section transparent and opaque 

 layers ; and beautiful works have been cut upon such specimens of this material. 

 The chalcedony and agate are, however, not unfrequently coloured artificially. The 

 layers vary very much in their structure, some being absorbent and others not so. 

 Such stones are taken, and if it is desired to have black and white layers, they are 

 boiled in a solution of sugar or honey, and then in sulphuric acid. The sugar or 

 honey is, in the first place, absorbed by the more porous layers, and then decomposed 

 by the acid. Eed or brownish-red layers are produced by occasioning the stone to 

 absorb a solution of sulphate of iron, and then by exposure to heat effecting the 

 peroxidation of the metal. This being done, layers very strongly contrasted in 

 colour are the result ; and very fine cameos have been cut upon stones so prepared. 

 See AGATE. 



In Italy and in France, the art of producing the cammeo duro has been to some 

 extent revived ; but the immense labour which such hard materials require renders 

 them so expensive, that these cameos have not come into general use. 



The shells of several molluscous animals are now commonly used. Many of these 



