[alt-photo] Re: Alternative sensitiser

[Peter Friderichsen]

Hi Sam,

The autotype patent that I refer to specifically mentions the use 
of  ferric salt, pigmented gelatin, and hydrogen peroxide for 
developing the image. There is no mention of casein in this patent. 
The patent also mentions that the process of "tanning" i.e. hardening 
gelatin by this method is "well known". It was that mention of 
tanning gelatin that had me wanting to do some tests using gelatin 
and other  natural protein materials i.e. casein, soy and gum arabic. 
I then came across Halvor's Chiba system document.

Re patent, search for GB665649 (GB is Great Britian) at the espacenet web site.

Thanks for the additional information on Franklin Enos. I did see his 
name mentioned in some research I did on casein printing although I 
never did come across any of his prints which would have been interesting.

I have not had a staining problem and have done tri-colour prints. 
The paper I am using right now is sized as purchased (Fabriano extra 
white -hot pressed) I was told it is internally sized with a waxy 
emulsion called AKD. I have not tried hardened gelatin sized paper 
but I wish to do this at some point.

I will be brief (as possible).  First, I prefer the green ferric 
ammonium citrate (FAC) as a 20% solution since it is more light 
sensitive, and for some reason allows for a smoother coat (I have 
tried the brown variety). There is one major problem that must be 
overcome however. FAC is somewhat acidic and it will cause the casein 
to curdle. You need to modify the FAC by upping the ph. You must 
alkalize the working sensitizer solution to get the pH up to about 6 
to 6.5.(I use a pool test kit which has phenol red as a pH indicator) 
You can go higher but it will hinder the sensitivity. The FAC 
solution will shift in colour slightly towards yellow-green. I use 
ammonium bicarbonate as the alkalizer which I can get at retail food 
stores. You can use sodium bicarbonate but the sodium seems to 
interfere with the speed, but it still works. If you go too alkaline 
just get it back with a little citric acid.

I use a 5% casein solution made from skim milk/vinegar. It is 
dissolved with a small amount of sodium bicarbonate to get it into 
solution. I make sure the final pH is around 7.

The peroxide needed is very dilute (0.1%) If you go above 3% the 
print actually will not develop as well, and it wastes a lot. ) 
0.1-1% range is good. You can add a small bit of ammonia to help with 
dissolving the emulsion (as you know).

I use a 1:1 casein/sensitizer ratio.

I hope this will help.

Peter Friedrichsen



At 02:13 AM 04/16/2010, you wrote:
>Hello Peter,
>
>Great to know that and to see your casein prints!
>
>Many years ago I learned casein from Franklin Enos, who till now was the
>only original source for the process that I know of. Franklin did a lot of
>original research in the 50's while he was vice president of French's, and
>had a copy of a patent but unfortunately I did not record the number.
>Perhaps that was the Autotype patent? Would you by chance have a copy or
>details about it?
>
>Your method of using ferric ammonium citrate and hydrogen peroxide is very
>interesting. I was using dichromate and a dilute solution of ammonia. I had
>a hard time finding paper that allowed multiple printing without staining.
>Obviously that's not the case with your method. I would be very interested
>if you care to elaborate it further.
>
>Thanks, Peter, for sharing!
>
>Sam Wang
>
>On Fri, Apr 16, 2010 at 11:35 AM, Peter Friderichsen <
>pfriedrichsen at sympatico.ca> wrote:
>
> > Sam,
> >
> > I have made some "gum" prints sensitized with ferric ammonium citrate. Use
> > those quotes because in actual fact I have used casein, and previously
> > gelatine that I modified to remain liquid at room temperature, 
> although I am
> > now working mostly with casein because it has such excellent clearing and
> > can manage a  high pigment load, although it has its own temperaments as
> > well. I have a few of these scanned and have posted them at
> > http://picasaweb.google.ca/pgfriedrichsen/AlternativePrints#
> >
> > Essentially the sensitizer is mixed in as you would dichromate. Exposure
> > time is equivalent to gum dichromate. The print must then be immersed in a
> > dilute solution of hydrogen peroxide (0.1%) is sufficient. (Oddly, this
> > system does not work with Gum arabic) I then flow water over the print for
> > about 1 minute and then hang it to dry. Dynamic range is about 5-8 steps on
> > a 21 step stouffer wedge. That is it.
> >
> > If anyone wants to go this route, be prepared to spend a lot of time
> > figuring things out because there really is little literature to go by with
> > the exception of a study done by Halvor Bjoerngaard of Chiba 
> University, and
> > it is quite informative. He coined it The Chiba system although it was
> > suggested more than 50 years ago, and the Autotype company had a patent for
> > this approach for use in making photographic stencils back in 1952.
> >
> > This low toxicity system is what I now use pretty well exclusively, and I
> > believe it is capable of producing excellent results, just not right out of
> > the box.
> >
> > Peter Friedrichsen
> >
> >
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