Re: A PVA for printing "gum" from Mike Ware

----- Original Message -----
From: "Ryuji Suzuki" <rs@silvergrain.org>
To: <alt-photo-process-l@usask.ca>
Sent: Sunday, April 02, 2006 1:47 AM
Subject: Re: A PVA for printing "gum" from Mike Ware

> From: martinm <martinm@gawab.com>
> Subject: Re: A PVA for printing "gum" from Mike Ware
> Date: Sat, 01 Apr 2006 15:54:11 +0200
>
> > In another paper (Lafond/Pizzocaro/Lessard/Bolte, Primary photochemical
> > process in films of dichromated gelatin: a quantitative spproach, Opt.
Eng.
> > 39, March 2000) the authors showed Cr(V) to be quite stable both in
> > dichromated gelatin and dichromated PVA. One of the most interesting
aspects
> > (at least for holographers) of Cr(V) consists in its strong absorption
band
> > around 520nm. That suggests it might be possible to "activate" a
dichromated
> > colloid (gelatin, PVA, possibly gum) with a weak overall UV exposure,
which
> > willl turn the Cr(VI) into Cr(V). Then the image exposure is carried out
at
> > a visible (non-UV) wavelength, preferably around 520nm.
>
> What's your goal? If the goal is amplification, it may work to a
> certain extent in converting Cr(V) to something else, probably
> Cr(III), but 520nm irradiation ("flash exposure") cannot create any
> additional imagewise Cr(V) so I think the degree of amplification is
> very limited, and nowhere near the developer in silver-gelatin process.
> Indeed, you may get all of the benefit of the flash exposure from
> thermal reaction, rinsing or semiwet plates. Don't you think?

The main goal is speed enhancement at 532nm. It may turn out that UV
pre-exposure will greatly increase speed for green light. No doubt, speed
will remain weak compared to silver halides. But DCG has some features
silver halides cannot rival: notably bandwidth and index modulation. By the
way, 532nm is the line where reasonably priced lasers fit for holography
(single frequency lasers) can be found relatively easily. So DCG holography
becomes accessible to amateur holographers. Moreover, that green line seems
to be important in the context of full color DCG. In addition, that green
wavelength being highly visible, is very pleasant to work with.

Martin
Received on Sun Apr 2 06:04:53 2006