[alt-photo] Re: Alternative sensitiser

[Kees Brandenburg]

Hi Peter,

Interesting results!  Can you tell us how you use the hydrolised gelatin? 
I really think ferric citrate can be a usefull hardener for colloïds. I have been working with Halvor's method (hi Halvor) for Carbon extensively and found a method to make a different protection layer without the agar-agar. I also have found some interesting ferric related patents. Apart from Autoype the Ulano corporation was very active too. That's were Kosar worked, for some time. I found strange patents too! Like the one using plain  ferric chloride as a hardener and ferric citrate as a restrainer. It claimed to speed up sensitivity but allways left me with a chewy lump of pigmented gelatin. A patent is not always  a true working process and often used to mislead others and hide the real stuff.

I earlier suggested zerochrome as a new generic prefix for these processes. Zerochrome-carbon, zerochrome-gum what do you think?

Kees






On 16 apr 2010, at 05:35, Peter Friderichsen 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