Making positive transparencies from negatives?

[benrains]

I imagine this is pretty easy question to answer, but what are the best ways to make b&w positive transparencies from existing film negatives? I'm not looking to create enlarged positives, although I suppose the process would be similar, but rather 1:1 copies. The idea of contact printing to regular sheet film had initially crossed my mind, but I thought I'd check to see if there's something else more suitable.

[Greg Lockrey]

First, the negative image is developed but the undeveloped silver halide salts are not removed by fixing. The negative image is removed by bleaching with a solution of potassium permanganate and sulfuric acid, which is removed by washing and a clearing bath containing sodium metabisulfite or potassium metabisulfite. The remaining silver halide salts are re-exposed to light, developed and fixed, and the film washed and dried. I may have more in the morning but I have to dig out my old notes from 20 years ago.

[benrains]

Greg, that sounds like a way to make positives from an original shot. (Which is still good to know. :-)

In my case I already have processed negatives that, in addition to making regular contact prints on paper, I'd also like to contact print onto film (to make a positive transparency). I'm just curious to know what sorts of film are well suited to being printed onto. Preferably it'd be one with a very clear film base, and ideally it'd have low enough sensitivity to light to allow time for darkroom manipulations like dodging and burning.

[Robert Hughes]

Try some slow speed ortho film for contact printing.

[benrains]

Try some slow speed ortho film for contact printing.

Thanks. Checking the ortho lithography film offerings on Freestyle and their accompanying descriptions, this sounds exactly like what I need.

[JRFrench]

Im not sure you want litho film, isn't that really high contrast? Something like the Rollei Ortho 25 from freestyle or something should be good. You can use a normal film like FP4 but you have to handle it in total darkness and the exposure will be fairly short. Safelight handling of ortho film will be very welcome, and its cheap.

As for processing a negative into a positive, Greg was on the money: http://www.darkroom.ru/info/manuals/...manual_eng.pdf

[domaz]

There is a bunch of resources on APUG about how to develop regular film as B&W slides. Just contact print them on regular film and go through one of those processes and you are good to go. They are not easy processes though- require mixing your own bleach etc..

[Robert Hughes]

The previous 2 posts are assuming the OP wants to make reversal slides, but in post #3 he says he has previously processed negatives and wants to make positive transparencies from them - essentially a negative of a negative.

Another way to handle this could be to scan the negatives, reverse to positive in Photoshop and print to transparencies. That would save a buncha film.

[Mark Barendt]

I think I read somewhere that one of TMax 100's design criteria was for this type of duping, Delta 100 would probably work too.

You biggest challenge will be defining the right exposure.

[Jim Michael]

Lith film is nice because of the clear transparent base (no blue or other tint like you often see in TX etc.) and it's nice and slow. It's high contrast if you use a high contrast developer (something with a lot of hydroquinone IIRC) but if you use a developer like HC110 etc. should be pretty normal tonal range like your original.