Uranium Toning

Eugene Robkin (erobkin@uwc.edu)
Tue, 10 Dec 1996 12:23:25 -0600

"When toning in uranium a considerable intensification of the the image is
effected. Allowance must therefore be made for this increase in density
when making a print, which should be rather thin and flat if the best and
most vigorous results are required with this bath.

The process cannot, however, be considered permanent ... if the print is
varnished with a thin coating of water varnish or gum ... uranium-toned
prints have been known to remain unchaged for a great number of years.

The prints should be very thouroughly washed to get rid of every trace of
hypo ...

The toning bath is made in two solutions, which keep indefinitely, and are
mixed in equal proportions just previous to use. The mixed solutions to not
keep, and must be used as soon as prepared: -

1. Uranium nitrate ------------------- 50 grs.
Acetic acid (glacial) ------------- 1 oz.
Boiled water ---------------------- 20 ozs.

2. Potassium ferricyanide ------------ 50 grs.
Acetic acid (glacial) ------------- 1 oz.
Boiled water ---------------------- 20 0zs.

The prints may be toned in this directly they are taken from the last wash
water. If they have been allowed to dry, they should be soaked in water
until limp before toning.

The toning solution must be kept in motion over the prints to prevent uneven
markings, and colours from warm sepia to Bartolozzi red are produced with
the greatest ease. When the desired colour is attained, the prints are
transferred to a dish of acid water (20 drops acetic acid to a pint of
water), and then washed by soaking face downwards in <+italic> still
<-italic> water. Washing in running water will remove some of the colour.
Washing is complete when the yellow tinge is discharged from the white of
the picture."

The grs. units are clearly grains. There is no entry I can find for the
water varnish mentioned for protecting the toned prints.

For what it is worth there is another toning formula claiming to give
Bartolozzi red, whatever that is, in the 1976 revised edition of
Photographic Facts and Formulas. That one used ammonium carbonate, copper
sulphate, and potassium ferricyanide. There are other copper based formulas
that claim to give various reds in other texts.

Hope this helps.

Eugene Robkin