SPECIAL PRINTING PROCESSES 485 



recommended under Multiple Printing is desirable. This, however, each worker must 

 decide for himself. It should be noted that gum-platinum printing is much easier than 

 straight gum printing; it is usually possible to get the same richness and depth of tone 

 with one printing of platinum and one of gum as with six or seven printings of gum 

 alone. 



Miscellaneous Notes. — Having no gelatin emulsion, platinum prints have no 

 tendency to curl; once flattened, they remain flat. 



With most papers, the surface has much more tendency to rub, especially when wet, 

 than is the case with bromide or gaslight papers. Therefore platinum prints should 

 never be processed in bulk, and they should be handled with some care. Damp or 

 dirty fingers placed on the surface of the paper at any time between sensitizing and 

 development will be almost certain to leave marks. 



Platinum paper is very hygroscopic and, if allowed to become damp, will give fogged 

 or degraded prints. Therefore it should be sensitized immediately before use and 

 developed as soon as printed. If it is to be kept for any length of time, it should be 

 stored in an airtight receptacle with a small amount of calcium chloride, which, being 

 even more hygroscopic than the paper, acts as a preservative. Even so, the length of 

 time which the paper can be kept without fogging is about 3 months. Old or fogged 

 paper can often be salvaged by the use of a small amount of potassium bichromate in 

 the developer, as described under Increased Contrast. 



Sometimes, through improper choice of paper or of sensitizing formula, the dry 

 print may have a dull, sunken look in the shadows; this occasionally results also from 

 letting the print soak too long in the developer or the clearing baths. In such a case, 

 the brilliant appearance of the wet print may be restored by simonizing, either 

 Simoniz wax or Old English Floor Wax being used; the former gives the print a 

 slightly greenish tone, the latter being a pure yellow. The wax is brushed as evenly 

 as convenient over the surface of the dry print and is then polished with a rather stiff 

 scrubbing brush, such as a nail brush or a vegetable brush. This polish, of course, 

 destroys the characteristic surface texture of the paper, and if this is not desirable, a 

 marked lightening of the shadows may be obtained by applying the wax as described, 

 then melting it into the paper over a gas flame or an electric plate, taking care not to 

 set the turpentine in the wax afire. The polishing should not be omitted, or the wax 

 will probably go into the paper unevenly, causing streaks. The yellow tone thus 

 obtained is often very valuable in the case of portraits or sunlit landscapes. It should 

 be noted that this waxing operation tends to make the print more brittle, so a waxed 

 print must be handled rather more carefully than an unwaxed one. 



Various methods of toning platinum prints to red, blue, green, and other colors 

 have been suggested. Since these depend chiefly on the use of salts of iron or uranium , 

 they impair the permanence of the prints and are not recommended. Von Hlibl has 

 shown that the warmth of tone secured by the use of mercuric chloride does not depend 

 on the addition of any other substance to the platinum image but is solely a question 

 of the grain size of the deposited metal. Therefore a properly cleared and washed 

 print is as permanent if developed with mercury as if processed for a pure black. 



Unless working on a very large scale, it is not worth while to salvage the platinum 

 from the clearing baths and the trimmings of paper. However, the developer should 

 never be thrown away; age does not impair its working qualities, and an older devel- 

 oper will contain a considerable quantity of platinum as well as of iron. This forms a 

 sludge at the bottom of the bottle, and for use the clear solution is poured off. A 

 certain amount of the solution, of course, adheres to the prints, so that the total bulk 

 must be kept up by the occasional addition of new solution, but the main body of 

 solution should never be thrown out; the developer which the writer is now using dates 

 back at least 25 years and is giving perfect results. 



