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Platinum-Iron Printing Papers 630

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PLATINUM-IRON PRINTING PAPERS 630. Platinum Papers. Pictures consisting of reduced metallic platinum may be obtained by methods similar to those indicated in the two preceding paragraphs by using potassium chore platinite instead of silver nitrate. The com mercial " platinum " papers are similar to kallitype paper in that they contain the ferric oxalate and the chloroplatinite and require to be developed in a solution capable of dissolving the ferrous oxalate formed (W. Willis, 1878).

Platinum prints, apart from the pigmentary quality of the image, which is not covered by any glossy coating, have the rare quality of being entirely unaffected by all the usual destructive reagents, that is, as long as the paper forming the support is able to resist them. Thus, platinum prints have been recovered intact from a sunken ship which was re-floated. after several years. Unfortunately, the ex tremely high price of platinum considerably restricts the use of this fine printing process. " Palladium " papers, with almost identical properties, have been used for some time, but even this metal reaches prohibitive prices.

Platinum papers are generally supplied in two kinds, giving black and sepia tones respec tively ; each kind is obtainable on various types of support, thin or thick, smooth or rough.

Platinum papers are extremely susceptible to damp, and are therefore usually supplied in metal tubes which have been hermetically sealed after desiccation ; when the original package is opened, the unused sheets should be kept in a dried atmosphere, for example, in a tin fitted with a double bottom containing drying materials.

Platinum papers are only suitable for making prints from negatives of fair vigour but not excessive in this respect.

Owing to their high sensitivity, platinum papers should only be handled in a very weak light, both when filling and emptying the printing frame, as well as when examining the progress of printing.

The sensitive surface of the paper is of lemon-yellow colour ; the image appears as purplish-grey, inclining to a light orange-brown in the densest parts of the shadows when fully printed. No details should be visible in the


Various toning processes have been suggested for platinum the toned images, however, no longer possess those qualities which dis tinguish a print on platinum paper, and at the same time are not of undoubted permanence. For these reasons the processes will not be described.

631. Use of Black-tone Platinum Papers. It is advisable to develop the prints almost im mediately after they are taken from the printing frame. If development is deferred for a few hours the papers should be kept away from damp.

Development may be done in either a hot or a cold solution ; printing should not be carried quite so far for hot development.

Development is carried out in weak daylight or in strong artificial light.

Extreme cleanliness should be observed throughout the operations. Glass dishes should preferably be used, as they are the only kind which can be properly cleaned ; for hot develop ment, an enamelled iron dish, free from cracks, and keipt solely for the nurnose. may be used.

For use, dilute with an equal volume of water.

Hot development is almost instantaneous ; cold development takes about one minute. No harm will be done if the immersion in the bath is prolonged, as the development ceases of its own accord when the ferrous salt, formed by the action of light, has reduced the equivalent quantity of platinum.

In point of fact, the hot-development process has now been practically abandoned, and is only used for the treatment of papers which are required to give sepia The dry print is usually floated face down wards on the solution. In order to do this, it is taken hold of by two opposite corners, so as to give the sensitive side a pronounced convex curvature. It is then lowered on to the surface of the liquid, and, when the lowest part of the paper is in contact with the solution, the two hands are gently lowered and the print released. After a few moments, it is raised from the bath to dislodge any air bubbles if necessary.

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