On Wed, 4 Jun 1997, Ron Silvers wrote:
<SNIP> I'm not sure that such a small difference of freshness
> would be enough to cause a 20% speed difference. I can't find the step
> tablet results for other papers that I've tested, but based on them I've
> had to recalibrate speeds to much higher differences than 20%.
I doubt it as well. I suspect that the componets in your batch from Brian
react differently than those of B&S. I have no experience with Brian's and
many years experience with B&S. Although I've been making it myself for
the last year and 1/2. You might contact Brian and ask him what his Sp.
Gr. and pH are.
I've recently checked two samples of B&S ferric that local prints used.
one batch with Ox acid = .3, another .5 with a meter with +/- .1. I got
it for $70. Something to consider. The Specific Gravity meter
(hygrometer) cost about $15. Tri Ess, VWR, etc... Items well worth
their expense.
>
> Yes, speed variation may come from changes in our equipment--I take it
> that being a good detective is part of the trade. But I still believe
> that mixture differences may well be the greatest source of exposure
> variations. I'll be watching out for speed changes for Brian's mixture as
> it ages.
>
> Eric, I don't add anything to the B&S mixture. As to a ph test: I don't
> have the necessary materials. An Sp Gr test? I don't know what that is.
>
Sp Gr is a Specific Gravity. The chart in Dick Stevens book show the
different Sp Gr for differing %s of solutions. Some ferric is more
concentrated than others. And after Dicks last posting on ferric, I
wonder what else is in his ferric. No disrepect Dick just a question.
Ron, the Sp Gr will be affected by the addition of anything other than
Ferric Oxalate, ie Oxalic Acid, EDTA, ferrous ions, whatever.
So the use of it as a test is helpful but not the definitive test for
purity. Anything that works and does not give you fog or weak images, is
probable OK.
Awhile back David was looking to make his prints warmer. A pH adjustment
upwards will do that. A pH of .3 will give you blacker prints. I make
mine at .7. Conversations that I've had with other printers, indicate
that platinum may reacte better with lower pH. I have not done the test
to check.
> And yes, Ginger as long as your kits were in powder form, they're still
> good. Welcome to the wonderful world of Palladium!
>
Although a caution about where might have been stored. Cool dark room OK,
HOt storage locker, maybe not 100%.
> Ron
>
>
>
EJ Neilsen
ejnasn@laplaza.org