Please Explain Lith Film!

I'm using it for transparent positive images from contact printed negs with tremendous success, but...

"What the heck am I using?" :confused:

Is it a silver gelatin on a very thin base? Are there incorporated dyes in the emulsion? I'm under the impression it's original purpose is super high contrast negs of screened B/W copy work for reproduction printing processes...is that correct? Is it still commonly used for it's intended purpose?

It just seems logical to want more details about the material, and web searches haven't revealed many details about the stuff.

Thanks in advance!

Jo

Lithographic films (Lith) were originally designed for the printing industry to make lithographic plates. The film was designed with ultra high contrast to yield essentially a black and white only image with no gray mid tones.

The size and number of dots formed in a lith plate were used to form mid tones from the black and white image.

A lith film was designed to work with a high pH lith developer to give optimum results.

This film was also used in copy work for line drawings and text pages.

There is nothing special about the emulsion except that it is made to give high contrast. It is blue sensitive only and has low speed. There is a section in Haist on this including an emulsion formula.

PE

Haist, p. 493:

"Analysis of commercial lith films has indicated that the emulsion is essentially a chlorobromide one, with chloride about 60 to 90% with a few percent or less of iodide, the rest being bromide. . . The classic lith photographic material has contained a cadmium chlorobromiodide emulsion"

I don't believe there is dye in it. Yes, it was used in the printing process and is not used widely anymore in the US but it is still used by some shops. Most of the pre press work is done with computers now.
I do not know a great deal about the compostion of lith film but I used it a great deal 20 years ago as I worked in a prepress shop. We did the film work for pages that were to be lithographically reproduced (printed with a printing press). Halftone films (dots) were made to reproduce photos, mimicking continuous tone, in print and line films were made for text and line art images and perhaps tint color boxes. Usually the film was exposed in a process camera, the 12 foot long horizontal types with like a 400 mm lenes. It was all quite fun in retrospect. The lith film is a fine grain material. Pretty much all the grain are similar size. The fine grain is was makes it slow, the uniformity of size makes it high contrast. The goal with line film was to have a density of opaque areas like 3.0 to 4.0 so that when the film was used to expose a printing plate it would it could stop the carbon arc light source used to expose the areas of the plate (clear area of film) intended to carry ink to the sheet of paper on press. All the pages were assembled in negative form.
I'm getting to ramble here. Anyway I don't much of the technical stuff but might be able to answer a practical question or two or certainly theroy of what it is used for i litho printing.
Some black and white photographers today use lith films to expose in camera and some use it for generating mask films used with enlarging and it is used in some of the alternatve photo printing processes. It is pretty fun stuff. developed in a print like developer such as dektol it has a bit of a curve and less D max. In the old lith developers it has NO curve and high D max.The old lith developers were a two part product, A B, that was combined right before use. It was potent stuff with paraformaldehyde and sodium hydroxide in it.
I recall the type of metals in the emulsions were changed over time with tighter environmantal regulations but as Michel states above cadmium, I heard talk of small amounts of mercury in some at times but I sure it was removed. The manufactuers were protective of their formulas.

Thank you, all, for your knowledgable replies!!

Jo