Re: uranyl nitrate and photo processing

["William Kolb" <William_Kolb_at_SETA@mail.hq.faa.gov>]

Early homebrew photographic formulas sometimes called for uranium as a
sensitizer in printing papers.  But even without the addition of uranium,
photographic films and emulsions normally contain 0.2 to 1.0 ppm of uranium,
which may increase considerably after photographic processes such as
intensification and toning.  The primary method of intensification is to render
the film image red, orange, yellow, or brown so that the blue light to which
printing papers is most sensitive was absorbed and image contrast is increased.
Uranium intensifiers produce a brick-red color almost opaque to blue light.  A
typical intensifier consists of equal parts uranyl nitrate and potassium
ferricyanide in a 10-percent acetic acid solution. Uranium replaces the silver
in films treated this way.  The variety of print tones available in black and
white photographic papers has always been limited to a few shades of brown and
brown-black. A much broader range of image tones can be achieved by using toning
baths after the print is developed. These baths either change the silver image
to silver sulfide or substitute another metal such as uranium for silver in the
image. Metal toning, as the latter process is called, offers the greatest
variety of colors, depending upon the metal used and the paper to which it is
applied. Metal toners usually proceed through a range of different colors in a
definite order and the choice of image tone is controlled by the time of
treatment. Uranium salts such as uranyl nitrate produced tones ranging from warm
black to brick-red.  Many of the newer photographic papers are not suitable for
toning and the amount of black and white processessing has declined markedly.  A
roll of B&W film now costs twice as much as a roll of color film.  With
inexpensive color materials readily available, the interest in toning has all
but disappeared. 

Few if any labs ever did toning or intensification, probably because of the
degree of personal taste involved in these processes.  Most, if not all
intensification and toning are done by the individual photographer.  Until say,
the late 50s, any well stocked photo store would have uranyl nitrate and anyone
could buy it off the shelf.  Now you need to order it from a chemical supply
house at $40-50 an ounce and shipping regulations require special handling
because it is a powerful oxidizer.  In agreement states, at least, uranyl
nitrate is treated as source material and no license is required to purchase it. 

bill


_______________________________________________________________________________
Subject: uranyl nitrate and photo processing
From:    radsafe@romulus.ehs.uiuc.edu at smtpgate
Date:    11/27/96  11:57 AM

Does anyone know if and when uranyl nitrate was used for photo processing?
 What quantities might be used in a typical photo lab?  And, whether this
compound would have been sold to exempt persons or generally licensed?

Please e-mail any info to:

BLHamrick@aol.com

Thanks in advance - you're all very helpful!

Barbara L. Hamrick
Los Angeles County Radiation Management
213-738-4148 phone
213-380-5630 fax