From: TERRY KING, 101522,2625
TO: Bas van Velzen, INTERNET:eland@knoware.nl
DATE: 02/06/96 09:23
RE: Copy of: Re: Copy of: buying Gum Arabic
Bas wrote.
pH 3-4, strong reductor specially in> alkaline solution> to
help in the confusion,
>
In relation to hardening gelatine for the initial size with sallysilic acid and
formaldehyde.
Bas's comments on red staining from Iron ( III ) when using salycilic acid were
interesting. Presumably this is what leads to 'foxing' in old maps and staining
in platinum prints. Is the Iron ( III ) in the atmosphere and being attracted to
the prints whatever one does. I have seen this staining in prints that I know
have never been anywhere near Iron (III ) during the processing.
As to pre-sizing, I observe these discussions with a detached and academic
interest. I would be interested to know what the practical effect of the
'strong reductor' in the formaldehyde method of sizing would be and I am
interested to learn that the hardeners can lead to the gelatine falling off the
paper.
The first coat of hardened size is recommended in some books and the
recommendation is followed by many as if it were holy writ.
I have been making gum prints successfully for many years. I have never applied
a gelatine size first, whether hardened or not. A good body and tub sized paper
will accept the first and second coats of pigment without staining; subsequently
one can size between coats.
The best papers for this method are Fabriano 5 and Bockingford. I find that
BFK, for example, does not work so well for this method and that is why I do not
use it for gum.
I have recently suggested to the list that a first coat of bichromated gum or
Gloy works very well as a foundation. Peter Frederick says that he has confirmed
this in tests he has made. The sensitised gum is dried in the dark and then
exposed for two or three minutes, and then washed to remove the traces of
dichromate, before the first coat of pigment is applied. I did think of a name
for this method.
The method works well for hot pressed papers.
Terry King