Clearing Bath
This is simply a 0.3% solution of hydrochloric acid. You will save considerably by purchasing Muriatic Acid from a hardware or pool supply store-this is essentially a 30% hydrochloric acid and is diluted 1 to 99 for use (10ml. in a liter of water). In its 30% strength, the acid is very strong and will burn skin and clothing, so wear eye protection and gloves to make several gallons at once, adding acid to the water, (not the other way around) slowly, while stirring. At 0.3% dilution the acid is very weak and fairly harmless. Keep the large supply stoppered as hydrogen chloride will evaporate into the air and cause problems in the darkroom. While there are several alternative clearing baths currently recommended such as citric acid and EDTA (a chelating agent) hydrochloric acid has the advantages of working well with a wide variety of papers, and if made more concentrated can act as a print reducer if palladium is present in the emulsion. This can leave the paper acidic and brittle, however, if the paper is not sufficiently washed and neutralized.

This is all that is needed to sensitize and process a platinum print once a paper is selected. The choice of paper has more effect on the final look of the print than any other single factor. Paper color, size, weight, and surface all influence the final look. For a paper to work well it needs to be sized sufficiently to keep the sensitizer from soaking into the paper too quickly- we need time to spread it around to get an even coating before it is absorbed into the paper. It also needs enough wet strength to stand soaking for half an hour or more, some of that time in the hydrochloric acid. Experimenting with different papers will most likely be frustrating before it is rewarding. If a paper will take a calligraphy pen and ink without bleeding, it is a likely candidate as long as it is 100% rag. Rising paper company's Gallery 100 is a good heavy weight paper and Strathmore 500 series drawing is a very good light weight paper, both used with the plate finish surface.

Before actually printing, we need to discuss the kind of negative needed to make a platinum print. The platinum emulsion is very slow and UV sensi-tive, making it out of necessity a contact process. The negative has to be the same size as the print you wish to make. A large camera can be used to make the negative, or an enlarged negative can be generated. Platinum doesn't have a straight line response to light as some claim, but it does have a much gentler toe and shoulder than silver resulting in more luminosity in the print. It is also softer, requiring a negative with more contrast than a negative made for silver printing. The smoothest platinum prints are made from emulsions with no added con- trast agent so the ideal negative would be made with this in mind. While the paper type and sizing does affect the printing speed and contrast of the emulsion, most papers work well with a negative that has a contrast range of 1. 7 or slightly less. Pyro, the traditional developer for platinum printing negatives, works well but requires a negative with a density range that would work well with a grade Ilh to grade 2 paper, because of the self-masking nature of the Pyro's yellow stain in this blue light sensitive process. Printing times will be approximately twice as long over that of conventional negatives..

Copyright (c) 1994 John Rudiak