Re: Tanning theory of dichromated colloids (was gelatin

"I was thinking of adding monomers to the colloid. I expect this to enhance
both speed and rigidity of the colloid. E.g. it actually might "replace" the
pre-hardening step - hence the handling of formaldehyde and the like."

Sorry, I thought your former "encounter" with glutaraldehyde was related to
gum printing.

"You just put dichromate with gum and go, that's all there is to it."

I see. So you are likely to be dealing with much higher levels of
crosslinking.
For holography dichromated gum, PVA etc. absolutely requires some sort of
pre-hardening.

Martin

----- Original Message -----
From: "Katharine Thayer" <kthayer@pacifier.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Monday, May 17, 2004 2:35 PM
Subject: Re: Tanning theory of dichromated colloids (was gelatin

> MARTINM wrote:
>
>
> >
> > I was thinking of adding monomers to the colloid. I expect this to
enhance
> > both speed and rigidity of the colloid. E.g. it actually might "replace"
the
> > pre-hardening step - hence the handling of formaldehyde and the like.
>
>
> Here you have lost me totally. Pre-hardening step? Formaldehyde? None of
> this is part of the gum process. You just put dichromate with gum and
> go, that's all there is to it. So I don't understand what you're talking
> about here.
>
>
> In
> > some areas grafting colloids seems to be a common thing. To give you an
> > example of a
> > graftet gum, see:
> >
> > "Synthesis and Characterization of Poly(methyl methacrylate) Grafted
from
> > Acacia Gum
> >
> > P. Chowdhury*, S. Samui, T. Kundu, B. Saha
> > Department of Chemistry, Siksha Bhavana, Visva-Bharati,
Santiniketan-731235,
> > India
> >
> > Abstract. Graft polymerization of methyl methacrylate onto acacia gum
> > has been studied in detail. The grafting was found to be optimal under
the
> > following reaction conditions: gum at 0.4 g/dL, monomer at 7.52¡Ñ10-2
> > mol/dL, ceric ammonium sulfate at 15.81¡Ñ 10-4 mol/dL, H2SO4 at 0.037
> > mol/dL, temperature at 50°C and time at 3.0 h. Fourier transform
infrared
> > spectroscopy was sed for the confirmation of grafting. Thermal and
physical
> > properties of the copolymer were studied. A probable mechanism of
> > polymerization has been suggested based on reaction kinetics."
> >
> > I suppose methyl methacrylate would not be particularly convenient in
the
> > context of a dichromate system. No doubt there are more promising (more
> > reactive and hydrophilic) monomers around.
> > With regards to the grafting catalyst ceric ammonium sulfate I am fairly
> > sure it would be compatible with dichromate.
> >
>
>
> I'm afraid that here you have lost me again. I don't understand what the
> point of adding this monomer would be. The dichromated gum process works
> fast and the hardened gum is quite rigid. It's impervious to dilute
> acid, to ammonia, and to boiling water either soaking or by pouring on
> with force. The only thing that I tried that disturbed the hardened gum
> was full strength household bleach. So I guess I don't understand why
> one would need to complicate the process by adding another step to speed
> up the process and add rigidity, as we really don't need more of either.
> Katharine
Received on Tue May 18 11:38:33 2004