From: Manuel Gomes Teixeira (punctumgt@netvisao.pt)
Date: 04/09/03-05:40:20 PM Z
Kerik,
Tomorrow I'm going to order Na2 for the first time from B&S.
It will be interesting and useful for all of us to hear some more details
of your and others experiences with this method of contrast control in
Pt/Pd printing.
I suppose that you use NA2 in substitution of K2PtCl4 when printing with
the classic Pt/Pd approach. Is that so ? Or is there any other more
complex procedures advised ?
Until now I've had better results with H2O2 added to the sensitiser
solution than with Potassium Chlorate.
My last question for today:
Why in all Pt/Pd literature is never advised to use Potassium Chlorate
solution added to the sensitiser as H2O2 and instead is added previously to
the Ferric Oxalate solution ? Is there any chemical explanation for that ?
Thanks for your time ! :-)
Kindest regards from Portugal
Manuel Gomes Teixeira
Punctum Studios
Aveiro
Portugal
> From: Kerik <Kerik@kerik.com>
> Reply-To: alt-photo-process-l@sask.usask.ca
> Date: Wed, 09 Apr 2003 11:09:12 -0700
> To: alt-photo-process-l@sask.usask.ca
> Subject: Re: hp and pot di with pt/pd
>
> Christina,
>
> HP in the developer will increase contrast somewhat, as others have stated.
> However, I really don't recommend this approach. The HP is quite unstable
> and the developer contrast character will likely change during the course
> of a single printing session. Enough to drive you nuts and waste time and
> materials.
>
> Sodium dichromate is more commonly used as a developer additive rather than
> potassium, although I would think potassium would provide similar effects
> if you balance the quantity of the dichromate relative to sodium. I say
> this because this approach has been standardized (by Phil Davis, I believe)
> based on a drop count of 50% sodium dichromate solution per a given volume
> of potassium oxalate. If you were to use potassium, I believe you would
> have to use more of it since it will only exist in solution at a
> concentration of about 11%.
>
> And finally, if you haven't already, I really recommend experimenting with
> B&S's "Na2" contrast agent which is added to the sensitizer rather than the
> developer. It gives you a much wider range of contrast adjustment than
> available with the dichromate approach, and it doesn't cause the
> degredation of print quality associated with the "Ferric Oxalate No. 2"
> approach that causes so many people problems when the are starting with
> this process.
>
> Kerik www.Kerik.com
>
>> Good morning!
>> Does anyone use either hydrogen peroxide or potassium dichromate added
>> to the developer or hp added to the sensitizer (the latter not for
>> palladium)?
>> Correct me if I am wrong here: added to the developer, dichromate will
>> increase contrast? And hp will decrease contrast? Why does this happen?
>> Chris
>
>
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