Given recent postings on Pt/Pd printing I thought people might be interested in
the following excerpt from the proceedings of the April 4 1877 meeting of the
Edinburgh Photographic Society where the first presentation of this new process
was made to a Society in the UK. Mr Willis himself was to be at the meeting but
circumstances did not allow. After an account of the principles involved that
seem to suggest that a print made using the ferric oxalate/potassium
chloroplatinate method will not print out,( when I left mine under the light for
a long time to see if they would, they did), Mr Rodger from St Andrews gave a
practical demonstration.
"For this process any kind of surface may be employed provided it be somewhat
porous, and it is better that it should have received a coating of organic
matter in the form of gelatine, or, preferably,arrowroot. In the commercial
prosecution of this process ordinary photographic or other good quality paper is
treated with arrowroot. This is now placed for a moment ona weak solution of
nitrate of silver ( six grains to the ounce) and dried: in this form the paper
may be kept for an indefinite time. When it is required to produce copies it is
only necessary to take a solution of the chloro-platinite of potassium and a
solution of ferric oxalate, mixed, and coat the sheet therewith; then dry and
expose under the negative. The picture on development may be considered beyond
the reach of change; but the colour of it is rather too black to please, and ,
therefore, it is desirable to modify it, and this is readily done by subjecting
it to a solution of gold for a short time. After the desired colour is obtained
it should be put into a weak solution of hyposulphite of soda or sol. chlor.
soda for a few minutes, and from that to water; and, finally, in order to remove
all traces of the feric oxalate, the print should be placed in a weak solution
of oxalic acid for as short a time as may be considered necessary, and then with
a slight amount of washing the picture may be hung up to dry."
There, easy, isn't it.
|What does the hypo do at that stage in the operation ? Why the salt ? And
what is the rationale behind the oxalic acid as a clearing agent.
"Trusting that I may not have wearied you in the foregoing remarks, and that a
spirit of enquiry may be aroused on the subject, I now conclude with my trhanks
to you for your patience and kind attention. "
Terry King