[rollei_list] Re: OT:Photographic Chemistry
- From: CarlosMFreaza <cmfreaza@xxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Wed, 24 Feb 2010 08:27:30 -0300
2010/2/23 Richard Knoppow <dickburk@xxxxxxxxxxxxx>:
> ... Glycin was widely used with PPD in the 1930s to make very fine grain
> developers. The problem with PPD is that it it has a very low development
> potential so it results in low contrast negatives unless time is extended
> for very long times and loses a very substantial amount of speed, as much as
> 5 to 7 stops! By combining it with glycin a more powerful developer can be
> made. The combined developer does not produce as fine grain as pure PPD but
> delivers greater film speed and has shorter development time...
Yes Richard, a normal developing process with PPD (10g) and sodium
sulfite (50g/1L water) takes 25' in average, if you add Glycin to the
formula (Edwal 12 formula I reproduced above) normal developing time
is about 19'; anyway Glycin is slow (but with strong potential) in
comparison with others developing agents, this is the Ilford ID 10
with Glycin only: ILFORD ID-10:
Water, 125F/52C 750 ml
Glycin 33.3 g
Sodium Sulfite (anhydrous) 26.6 g
Sodium Carbonate (monohydrate*) 166.6 g
Cold water to make 1L
* = 142.5 g Sodium Carbonate (anhydrous)
Developing time is about 20', BTW you need several developing time
tests with these old formulas and it's interesting to note that
decades ago developing times were given at 18ºC mostly and they are
given at 20ºC today and then you can find discrepancies for the same
formula suggested developing times according the source.
Glafkidès suggests the no toxic or less toxic paradiamine-sulfonamide
as good replacement for the PPD.
Carlos
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