Any PPD will work. In my comments the term PPD is meant to include the basic compound and all of its derivatives up through CD6. They all work, but need a boosting agent to achieve the true speed of the emulsion. Above posts indicate what some of them are. They work fine, but you have to understand the underlying chemistry that is working here before you come up with a suitable formula that works. It can yield outstanding results. These formulas were developed (pun unintended) in KRL but never commercialized. I have no exact formula.
PE
Yes - thank you. Well the work of the
underlaying chemistry before coming
to a fine formular is indeed not simple
on ones hand.
I should have some of the very early formulas with PPD (long before Edwal's 12) - I just have to find them.
As I have it in mind - these formulations
comming from pre 1900 and they are in use with a "boosting agends" I mentioned it as superadditives.
Still 1900 there was a need of a "second
develloper" to make PPD usable.
It is mentioned here before as a " losy"
allone developer agend.
That should be absolute correct.
As I remember the very early formulars
I have - are with some speculations for
all of the used chemical compounds.
Because it was the work of very early
photographers - so there were formulars
in often "variations" as a secret from many.
As I understood they have the superadditives to PPD in use (from year to year )
witch were the modernest at the time.
So you have just have a look to the history of developer agends and the concerning period - and you know
whant was in use - the latest agend.
But with speculations on correct formulations. (very lots of variants).
As a result - the Asa rates comming up
from decade to decade as combination
of new emmulsion improvements and
better developer agents.
BUT in the very early years they used
PPD "allone" developer with very bad
results due to insufficient speed.
Yes - the correct working formular is
a mystery - but very interessting because
"Forgotten" !
with regards