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

On Mar 29, 2006, at 6:02 PM, Katharine Thayer wrote:

>
> Why the people who want to reproduce gloy want to do that, they'll
> have to answer themselves. But it's probably worth emphasizing,
> since the things seem to have gotten confused, that however gloy is
> made or approximated, PVA all by itself works fine for a
> dichromated colloid process, as Mike's student demonstrated and as
> holographers and researchers have been proving for quite a while,
> and that's why it makes some sense to use dichromated PVA as a
> standin for dichromated gum in trying to understand the
> crosslinking mechanism, especially since most researchers believe
> that the crosslinking mechanism is probably the same for both PVA
> and gum (although maybe not the same for gelatin).

I can't find Ryuji's post that asks me this question, but looking at
the Bolte et al paper I was reminded that Ryuji asked me the other
day to explain my rationale for this last statement. I'm not sure if
he meant the first part (that the crosslinking mechanism for PVA and
gum are probably the same) or the last (that gelatin may be
different.) I'll assume the latter, since the fact that when I asked
a question about gum crosslinking, Ryuji cited a paper about PVA
crosslinking, suggests that he's probably in agreement with the
former. As to the latter, I'll quote the Bolte paper again (the
introduction): "For a long time chromium (III) the final chromium
species was thought to be responsible for the crosslinking process in
dichromated systems. This assumption is quite logical with
dichromated gelatin, chromium (III) being the only chromium species
remaining after development. On the contrary, it is more surprising
when dealing with dichromated PVA, a material in which chromium (V)
has been proved to be stable..." I suppose it's statements like that
which make me wonder if maybe the mechanism for gelatin might be
different than that for PVA/gum.
Katharine
Received on Fri Mar 31 09:42:50 2006