[alt-photo] Re: Alternative sensitiser

[Peter Friedrichsen]

Kees,

In regards to the slow hardening of gum. I believe what you say in 
regards to the slowness may be the problem. I did an experiment once:

I added a ferrous salt to gum arabic and it remained liquid. I then 
added a few drops of hydrogen peroxide to the solution to convert it 
to the ferric form, and it immediately hardened as a clumpy 
precipitate. The same thing happened with gelatin but perhaps it just 
is not quite fast enough with gum, when the peroxide has to compete 
with water dissolving it off the paper surface. The only conclusion I 
was able to draw here is that the ferric/peroxide will harden gum. 
Perhaps something can be done to slow the dissolution and give it more time.

Peter Friedrichsen

At 04:51 AM 04/19/2010, you wrote:
>Thanks Peter!
>
>Is the pineapple enzyme in the juice of the fresh fruit? Just press it?
>
>The problem with gum and ferric ammonium citrate for me was that the 
>exposed emulsion floated of the paper in the peroxide bath. The 
>peroxide doesn't have the time to do it's hardening I think. It 
>seems to work though with the hydrolized gelatin and maybe even 
>better with casein as your prints show.
>
>Kees
>
>
>On 19 apr 2010, at 00:54, Peter Friderichsen wrote:
>
> > Kees,
> >
> > To mildly hydrolyse the gelatin, you can either acidify, or 
> alkalize it, then heat it for a limited time, or use an enzyme like 
> that from fresh pineapple. They all seem to result in different 
> surface properties of the gelatin which now is liquid at room 
> temperature and whose prints produced from such, can be developed 
> at room temperature.  M. Carey Lea first made something like this 
> which he called meta-gelatine.
> >
> > You can keep this for some time at room temperature if you add 
> the right preservative, but like any gelatin in solution, it will 
> slowly auto-hydrolyse (much slower if kept cold), and the result 
> will be weak prints. At room temperature, I find it works well for 
> about 6 weeks. Gum arabic as you know seems to last much longer if preserved.
> >
> >
> > Peter Friedrichsen
>
>_______________________________________________
>Alt-photo-process-list | http://altphotolist.org/listinfo