Re: x-ray film

There are two different kinds of x-ray films.

One kind is for direct x-ray exposure. Films of this type have low
sensitivity to light (despite large grains) and they do not use
sensitizing dye. The x ray-optimized emulsions and light-optimized
emulsions are different in terms of grain composition (e.g., iodide
content), prefered kinds and doses of dopants used, and the use of
sensitizing dye (i.e., x-ray emulsions do not use a sensitizing
dye). Increasing x-ray sensitivity does not mean increased light
sensitivity. It's often opposite. Absorption of x-ray by silver halide
is very low, that is, the film is virtually transparent to x-ray. This
is why direct exposure x-ray films are very thickly coated on both
sides to enhance sensitivity. These emulsions are also minimally
hardened to increase Dmax. Although the manufacturers have worked to
increase the degree of hardening without compromising image quality,
the level of hardening is nothing like what we see with pictorial films.

Another kind of x-ray films is for screen exposure. This is used in
combination with green flurescent screen (phosphor screen) and these
are light-optimized emulsion with an appropriate green sensitizing dye
matched to the screen. The film has high sensitivity to green
light. The films contain higher level of silver (called coating
weight) than average graphic art films, but it's probably comparable
to fast camera negative films and nowhere near that of the direct
exposure x-ray films.

Both types of x-ray films are used. Screen exposure requires less
x-ray dose. Direct exposed x-ray images are generally much sharper
than screen exposed images. X-ray does not cause diffraction and
scattering like light does, so x-ray with a knife edge is the
preferred method of exposing film when adjacency effect is studied.

Standard developers for x-ray films are not too dissimilar from DS-14.

I wouldn't be excited with x-ray films for alt uses.

Ryuji

From: Etienne Garbaux <photographeur@softhome.net>
Subject: Re: x-ray film
Date: Sat, 26 Nov 2005 00:47:29 -0500

> John wrote:
>
> > Has anyone played around with x-ray film for alt purposes?
>
> X-ray film is generally coated quite heavily on both sides with a fairly
> fast, fairly contrasty blue-sensitive or, sometimes, ortho (blue + green
> sensitive) emulsion. These days, the image is formed largely by
> fluorescence from phosphors in the film holders (as opposed to directly by
> the X-rays), which allows for much smaller X-ray doses. Because of the
> thick emulsion on both sides, it has huge amounts of silver in it -- silver
> recovery is not optional for X-ray labs. I've never tried using it for alt
> work -- I assume getting the back side exposed without the phosphorescence
> could be problematic.
>
> Best regards,
>
> etienne
>
Received on Sat Nov 26 00:37:56 2005