Modified Platinum printinggreenspun.com : LUSENET : Large format photography : One Thread
This is some thing which I am interested in, as I understand, you can only make platinum prints the same size as the negatives used - however would itbe possible to replace the cold cathode lights in an enlarger with UV lights to expose the paper and therefore allowing perhaps the 6x7 user to print up to 20x24 or what?
-- David Kirk (David_J_Kirk@hotmail.com), March 24, 2000
-- Bill Mitchell (email@example.com), March 24, 2000.
There is at keast two problems with this approach that I know of, and there may be more. First, the platinum or palladium mixtures are very insensitive; they often take 10-20 minutes of exposure under very high light levels (or in sunlight maybe 5-10 minutes) to achieve proper exposure. It would be nearly impossible to produce an enlarger that could andle that amount of light (and heat) without major problems.
Second, the optics in an enlarger lens are not designed for UV light, which is the range of wavelengths that these mixtures are sensitive to. So, you would need to search out some highly specialized enlarging lenses that will focus UV wavelengths (and not absorb or reflect them, as most optical glass tends to do.)
So, your best option is to make an enlarged negative to use for contact printing. This can be done in the traditional method, or with digital methods. Dan Burkholder has a book out about the digital method. You may want to look it up.
The internegative will also allow you to make a negative that has the proper density range that is necessary for platinum or palladium printing (normally about 1.35 for platinum, and 1.6 for palladium, if I remember correctly.)
-- Michael Mutmansky (firstname.lastname@example.org), March 24, 2000.