>>Could someone describe the dichromate method of contrast control? Sorry if
>>this repeats earlier posts. Thanks.
>>V6263@aol
>
>This method works with Potassium Oxalate developer only. As incrasing
>amounts of Sodium Dichromate are added to the developer it increases in
>contrast (and, as with other restrainers in other developers, decreases in
>speed). Dick Arentz has the details in his book on Pt/Pd printing, but my
>copy of his book is on loan to someone. Perhaps someone else on the list
>can give the mixing and dilution formulae.
A 50% solution of Sodium Dichromate is added to Potassium Oxalate (KOx) as
follows:
Bottle # Na2Cr KOx
0 -------- 200ml
1 1 drop 200ml
2 2 drops 200ml
3 4 drops 200ml
4 8 drops 200ml
5 16 drops 200ml
6 32 drops 200ml
7 64 drops 200ml
I use 2 liter bottles and top them off in 200ml increments as needed. As
with plain KOx, it does not go bad and can be replenished indefinitely. A
recent step-wedge test of the full range (O-7) confirmed this. This set of
developer bottles has been in use since the fall of '95.
I have found that this method works better with a mixture of Pt & Pd than
with Pd alone. With straight palladium, I find that with #4 and higher there
is a bleaching of the shadows i.e. a loss of density (Dmax = 1.2 or 1.1
rather than the usual 1.4 or higher).
According to Arentz, this method was worked out by Phil Davis.
Best wishes,
Keith Schreiber