>I quote directly from the sheet "USING ARCHES PLATINE PAPER":
>Develop for two minutes.
>Rinse.
>Clear in acid baths, two baths eight minutes each. (4% citric acid)
>Rinse.
>Final clearing in sodium sulphite bath for five minutes. (minimum 2%)
>Wash for twenty minutes.
Can I follow up with some more questions/comments to try to help resolve
this problem?
What developers are recommended? The pH (degree of acidity/alkalinity - for
the non-chemists) at this point in the processing could be critical in
deciding the state of hydrolysis of the iron(III) and therefore the ease of
its subsequent removal. Precipitated iron hydroxide slowly converts into a
highly insoluble form that cannot even be removed by dilute acids and
chelating agents.
The water rinses could also be a source of trouble in allowing the pH to
become less acidic. Old textbooks (which deal with the 'traditional'
platinotype) specifically warn *against rinsing in water* between developer
and acid clear baths, otherwise yellow stains tend to arise. I think this
would depend very much on the pH of the developer.
The "final clearing in sodium sulphite" is essentially the same as using
HCA - but many years ago I found this to be more effective if placed
*before* a final bath of tetrasodium EDTA.
I am sure Keith is right when he says:
>and always there remains a faint yellow stain around the edges. I wonder
>if those printers who do not mask the edges of their prints might not
>notice such a faint stain.
Masking at least part of the sensitized paper from any light exposure
provides an essential 'telltale' for imperfect clearing. I am convinced
that the 'lovely warm creamy-yellow' highlight tones on some historic
platinotypes (which usually have no margins at all) are due to iron
residues.
Keith also asks:
>Mike, do you know if there is a source for the Buxton and Van Gelder
>papers in the US?
Buxton - no, definitely, (see my other post); Van Gelder - I couldn't say.
>If not would you post the address and telephone for John Purcell Papers,
>>London?
John Purcell Paper
15 Rumsey Road
London
SW9 0TR
UK
tel: +44 (0)171 737 5199
fax: +44 (0)171 737 6765
The man to ask for is Jeremy Youngs, who is well-acquainted with our needs
for paper, and has been very helpful. I have no commercial interest -
except as a satisfied customer.
I'll say a bit more about the paper problem in a separate post.
Mike
Dr. Michael J. Ware
email: mike@mikeware.demon.co.uk
snailmail: 20 Bath Road, Buxton, Derbyshire, SK17 6HH, UK
phone and fax: +44 (0)1298 78604