Hi All,
Selenium is extremely nasty stuff that many photographers won't even touch;
I believe it's safe enough at room temperature (with skin contact avoided),
but a boiling solution does give off toxic fumes. I make mine in the open
air, usually 25 litres at a time, in an aluminium "Burco" boiler (which, I
understand, was used in the old days for cleaning dirty nappies/diapers).
The toning solution attacks other metals, so I've had to replace the tap
with a nylon one from a home-brew shop.
The published Kodak recipe (T-55 or T-56, I forget which) contains about 6g
of selenium per litre, but I could never get it to dissolve completely, even
with boiling for an hour. I don't remember the Kodak formula exactly, but
I've modified its quantities as follows. so that the selenium should
dissolve fully in less than 30 minutes:
Sodium sulphite 140g
Selenium powder 5g
Ammonium chloride 140g
Water to 1000ml
Dissolve the sulphite in hot water, bring to the boil and add the selenium.
Boil for as long as necessary, then stir in the amm. chloride. Kodak said,
I think, that the solution should be cool before adding the amm. chloride,
but it dissolves much easier in warm/hot and does not seem to make any
difference. The toner is then diluted 1+5 for use, at which strength its
action is roughly equivalent to Kodak Rapid Selenium at the 1+3 dilution.
Maybe selenium came in a different form in the 60s and further back (which
Clerc appears to confirm), but you're not alone in finding that specified
quantities do not always dissolve completely. I once tried to speak to
someone at Kodak about their selenium recipe, but they knew nothing about it
and denied it was one of theirs. If I got that in writing, maybe I could
patent it...
Finally, a bit of info from Clerc:
The use of selenium in the form of seleno-sulphate* (with ammonium chloride
added) for toning print-out papers was suggested in 1912 by P. Rehlander as
being more economical than toning with gold and platinum. [Clerc says
elsewhere that the same solution is fine for development papers.] Even with
papers that have been well washed to remove the soluble silver salts, toning
with sodium selenosulphate tends to stain the whites of the image very
strongly. This trouble can be obviated, when toning is done after fixing
and washing, by adding a small quantity of sodium hyposulphite [what they
then called sod. thiosulphate, or hypo] to the toning solution (Lumiere and
Seyewetz, 1924). This procedure greatly increases the speed of toning. The
tones obtained vary from dark brown to red**, according as the image is
coarse or fine grained; this toning gives (with certain papers) an
appearance of platinum toning when used on a print which has been toned with
gold and fixed.
Sodium selenosulphate may be obtained by dissolving 260 gr. of powdered
selenium in 20 oz. (30 grm. in 1,000 c.c.) of a warm 20 per cent solution of
anhydrous sodium sulphite. [No way!! But see first footnote - doesn't
sound like the selenium I buy. Liam.]
Twenty to 50 minims of this solution are added to 20 oz. of a 30 per cent
solution of hypo (2 to 5 c.c. per litre of hypo solution). The smaller
quantity is used for toning albumen papers and the larger for emulsion
papers (gelatine or collodion P.O.P.). The bath is limpid, colourless, and
keeps well.
Toning is very rapid, taking from 2 to 5 minutes, according to the degree of
exhaustion of the bath. This toning solution is very economical; 35 oz.
(1,000 c.c.) will tone 80 prints 7 X 5 in. in size, and the results are
highly permanent if washing is properly done.
* Selenium, which in many of its properties resembles sulphur, appears
usually as grey crystalline masses; in a fine state of subdivision it is
generally red. The alkaline selenosulphates, and particularly the sodium
salt (Na2SSeO3), have a constitution which is closely analogous to that of
the hyposulphites (Na2S2O3), the selenium replacing a portion of the
sulphur. Just as thiosulphate is obtained by dissolving sulphur in a hot
solution of sulphite, so selenosulphate is obtained by dissolving selenium
in hot sulphite solution. As selenosulphate is not made commercially it
must be prepared as required by dissolving selenium. Solutions of
selenosulphates should be kept in full bottles, well stoppered to avoid
conversion into inactive selenotrithionates by oxidation; they are more
stable in presence of sodium sulphite or hyposulphites. Analogous compounds
of tellurium have also been used for the toning of silver prints.
** The ratio (1:0.88) in a long while toned print is greater than that for
silver selenide (Lumiere and Seyewwtz). The selenium is deposited on the
silver without combining with it until each grain of silver is completely
enclosed in selenium.
[In recent times, there have arisen serious doubts about the ability of
selenium to protect silver images against oxidation, which others on this
list can probably say more about.]
Liam
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