Kevin O'Brien (kob@paradise.net.nz)
Sat, 13 Feb 1999 13:17:50 +1300
I have done reversal processing of b&w and even Cibachrome.
I can't find the R-21 formula amongst my collection but it appears to be the
old sulphuric/permanganate bleach which is also useful prior to
re-development or toning.
The formula I have is:
Sol A Pot permanganate 0.4% w/v (2gm in 500ml water)
Sol B Sulphuric acid 2% soln (10ml in 500ml water)
Clearing bath sodium or pot metabisulphite 2.5% soln. (25g in 1t water)
Kodak in its 1977 edn of formulas gives R-9:
Water 1.0 liter
Pot Dichromate anhy 9.5gm
Sulphuric acid conc 12 ml
with 1.1% w/v clearing bath of sod sulphite anhydr.
For those not wanting to use sulphuric acid this works well as a bleach:
A. Pot bichromate 5% soln
B. Hydrocloric acid 10% soln
To use A is diluted with 6 vols of water and an amount of B varying from 1/4
to 4x the amount of A is added. The less hydrocloric the slower the
process.
The yellow stain washes out and can be removed completely with 1% pot
metabisulphite soln.
If these are considered hazardous - try a bleach made from mercuric cloride
or pot cyanide! (Formulae available on request).
Concentrated acid given appropriate care is no more hazardous than what we
normally work with. When diluted to stock solns for storage it is relatively
safe.
Kevin O'Brien
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