Fixing of a kallitype

Dear members,

When I started reading articles (papers ?) about fixing I got into disorder.
At first because every author gives a different quantity of sodium
thiosulfate per liter and a different receipe and a different time.
Sandy King: 50 g/l + 10 g Na2CO3 + 2g Na2SO3
                                             time: 240 sec. or 2 x 120 sec.
Judy Seigel: 55 g/l + 10 ml ammonia
                                             time: 120 sec.
B & S : 25 g/l time: 15 sec.
Keepers of : 50 g/l + 6 ml ammonia
    Light time: 300 sec.
Dick Stevens: don't know what he is saying about it .
WHAT IS CORRECT ?
Second: Do they use
    sodium thiosulfate : Na2S2O3 CAS: 7772-98-7
or sodium thiosulfate.pentahydrate : Na2S2O3.5 H2O
                                 CAS: 10102-17-7 . Most common.
The same with:
    sodium carbonate : Na2CO3 CAS: 497-19-8
or sodium carbonate.monohydrate : Na2CO3.H2O
                                                    CAS: 5968-11-6
or sodium carbonate.decahydrate : Na2CO3.10 H2O
                                                    CAS: 6132-02-1
or sodium carbonate.hydrate : Na2CO3.aq
                                                    CAS: 24551-51-7
WHAT IS THE RIGHT STUFF ?
Third: What is the concentration of the used ammonia ?
          Is it 5%,10%,15% or even more ?
( In the Netherlands 5% is usual as household ammonia but you can also buy
15% )
TIP : sodium thiosulfate.pentahydrate (CAS 10102-17-7)
        cools on dissolving
        sodium thiosulfate anhydrous (CAS 7772-98-7)
        heats on dissolving
(SPSE Handbook of Photographic Science and Engineering
 page 528 ISBN 0-741-81880-1 (1973)
                  ISBN 0-685-20939-3 reprint
                  ISBN 0-608-17768-7 reprint )
But the most confusing to me is the (low) concentration of
sodium thiosulfate.
As a student I learned that fixing in standard photography is
a very complicated chemical process.
First step: 2 AgBr + Na2S2O3--> 2 NaBr + Ag2S2O3

(insoluble)
Second step:
    Ag2S2O3 + Na2S2O3 <--> 2 Na(AgS2O3) and
    Ag2S2O3 + Na2S2O3 <--> Na2Ag[Ag(S2O3)2]
                                                 (slightly soluble)
Third step :
    Na(AgS2O3) + Na2S2O3 <--> Na3[Ag(S2O3)2]
   Na2Ag[Ag(S2O3)2] + Na2S2O3 <--> Na4[Ag2(S2O3)3]
  Na2Ag[Ag(S2O3)2] + Na3[Ag(S2O3)2] <-->
                                           Na5[Ag3(S2O3)4]
Because all the reactions in the second and third step are
equilibrium reactions you need a large excess of sodium thiosulfate Between
18 C and 21 C (for Americans : between 64 F and
 70 F ) the optimum is a 40-50 % solution.
(Photography for the scientist. Ed: Charles E.Engel
                        1968. Academic Press N.Y.
page 260. No ISBN
      Library of Congres Catalog Card number: 66-16698. )

Mostly used : 20 % solution
WHAT IS THE REACTIONMECHANISM OF FIXING
IN KALLITYPE ?
IS FIXING OF A KALLITYPE SO TOLERANT THAT IT DOESN'T MATTER HOW YOU'LL DO IT
?

I am really interested in soundly based answers,so please don't
tell me stories with : "when I remember well.. " or "I am not quite
sure... " or "I believe that..." etc.
There are already (too) many articles whit presumptions,
suppositions and idle thoughts on internet.
Kind regards
Erich
Received on Sat Dec 13 00:08:17 2003