tw (01/08/83)
#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