Liam Lawless (lawless@vignette.freeserve.co.uk)
Wed, 17 Feb 1999 03:22:28 +0000
Hi everyone,
I'm glad to see continued interest in the reversal method, but surprised at
all the fuss over the bleach. Everyone is apparently terrified of sulphuric
acid, but the P-F article clearly states that 10% strength solution can be
used instead of concentrated: use 500ml of 10% rather than the 50ml of conc.
specified in the recipe, and, by reducing the amount of water added, you
still end up with 1 litre!
If 10% sulphuric is still a problem, use 50g of sodium bisulphate instead of
the sulphuric. I haven't done this myself and can't say whether it will
affect the speed of bleaching, but it WILL work.
The T-Max reversal bleach described by Mac will certainly work if it is
indeed permanganate and sulphuric, but this requires a different clearing
solution of 5% sodium (or potassium) metabisulphite [50g sod. meta. in 1
litre water]. T-max bleach might be stronger or weaker than R-21, but this
isn't important - it just means that it may work a bit quicker or slower.
Perhaps I should repeat the warning on sulphuric for the benefit of anyone
who might have heard of the reversal method from some other source than
Post-Factory. Water MUST NEVER be added to concentrated sulphuric,
otherwise it will boil violently and spray out of the mixing vessel. To
dilute, the acid must be added to water, very slowly. Much heat is
generated, even with 100ml of acid added to 900ml of water. But a drop of
the stuff on your finger won't kill you, though it might sting a bit on an
open cut. Not a good idea to put it in your eyes, so wear suitable
protection and make sure there is plenty of clean water nearby in case it's
needed.
Hope this puts everyone's mind at rest,
Liam
This archive was generated by hypermail 2.0b3 on Sat Nov 06 1999 - 10:06:51