From: utzoo!decvax!duke!harpo!seismo!hao!hplabs!hp-pcd!tw Newsgroups: net.rec.photo Title: Lith film info - (nf) Article-I.D.: hp-pcd.570 Posted: Fri Jan 7 18:02:23 1983 Received: Sun Jan 9 01:57:42 1983 #N:hp-pcd:7800011:000:2776 hp-pcd!tw Jan 7 12:16:00 1983 >From harpo!fortune!wdl1!rmb Thu Jan 6 16:11:23 1983 To: fortune!harpo!hp-pcd!tw Subject: please forward Please forward to net.rec.photo, our inews is fubar. Subject: Lith film info There is a Kodak book called Creative Darkroom Techniques that has a very good step-by-step description of lith film processing. This book also covers toning, photo-silkscreens, intensification, reduction, and solarization. It is well written, and full of very good photos. It's definitely a cut above the general Kodak "any amateur could do this" level. If it's not on the shelf at the photo shop, ask for the Kodak L-5 Index. This is an index to all Kodak publications, about 1000 titles, as I remember. I think that Creative Darkroom Techniques is known as 'AG-18' to the Kodak order department. You can even get your own L-5 index -- mine is about five years old, and was free. About Lith Film: The name comes from Offset Lithography Printing. Making plates for printing probably uses 99.9% of the lith film manufactured. Printing requires a "binary" image -- ink or no ink. Lith film (and lith developer) is designed to do this. Exposure below a certain threshold leaves the film clear; above that threshold, the film is much darker than normal film. The transition takes place in about one-third stop. The exact location of the threshold is dependent on the developer, the age of the film, etc., so it is wise to bracket the exposure generously. Lith films are also called line films, and regular films are called continuous-tone films. These terms come from the world of copying. If you are copying a line subject, something that is white and black with no greys, like a printed page or a schematic, you want the copy be white and black, not light grey and dark grey. Line films do the trick. If you are copying a something with greys, like a photo or a pencil drawing, you use continuous-tone film. Line films do *not* give an image that is black up to threshold one, clear from there to threshold two, and black thereafter. Someone suggested that line film worked like that. It does not. Such a film would require negative processing for one emulsion layer and positive processing for another layer. It might be possible to make a film like that, but it is easier to do the trick using lith film. Make two exposures, make a positive of one of them (that is, make a negative of the negative), and sandwich the two. The other distinguishing characteristic of lith film is its powerful attraction for dust. Nothing shows dust spots like an expanse of solid black. Luckily, dust is easy to fight. You can blob on Kodak Opaque to cover clear spots in the black, and cut out a piece of the film to remove black spots in the clear. Simple, huh? wunderwood