The Dictionary Of Photography

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Platinum                                               Platinum Toning
" i st. Coating the paper. This may be done with either uranic chloride, ferric oxalate, or sodic ferric oxalate, or a mixture of any or all of these.
" 2nd. Exposure.
"3rd. Development. Half a drachm of a 15-grain solution of sodio-chloride of palladium is diluted with about 1 oz. of water, and the print floated thereon face downwards. It is better to add a trace of hydrochloric acid to the developer.
"4th. Fixing as in platinotype.
The result will be a print like a platinum print, only of a pleasant warm tone, which may be rendered colder by adding a trace of platinum to the developer. For particulars of the printing-out platinum method, see Pizzighelli's Printing-out Process.
Platinum (Ger., Platin; Fr., Platine; Ital., Platino). Pt = 1967. Synonym : Platina. This metal occurs usually in the free state, the chief source of supply being Mexico, Brazil, and Siberia. It is a silvery white metal, having specific gravity 21*5. When in an extremely fine state of division, it is black, and is one of the most permanent and immutable of all metals. It is tolerably hard, very difficult of fusion, not dissolved by hydrochloric, nitric, or sulphuric acid, and only slightly acted upon by some alkaline substances.
Platinum Perchloride. Synonyms : Tetrachloride of Platinum, Platinum Chloride, Platinic Chloride, Muriate of Platina, Chloroplatinic Acid. This salt is prepared by dis-solving metallic platinum in aqua regia. It occurs in small brownish-red masses extremely deliquescent, forming a deep orange or brownish-orange solution. Very soluble in alcohol and water. It is used for preparing chloroplatinite of potash, and has been used for toning prints and collodion positives. This salt readily combines with the chlorides of potassium, sodium, and ammonium to form double salts - e.g., PtCl42KCl.
Platinum Toning. Either with the desire for greater variation in the tones, or for possible greater permanence of the image, platinum has been applied to the toning of silver images, and whilst rich brown blacks and cool sepias are obtained it does not seem possible to obtain pure blacks as when using platinotype paper. There are several conditions which are