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

On Mar 29, 2006, at 3:24 PM, Judy Seigel wrote:

>
>
> On Wed, 29 Mar 2006, Katharine Thayer quotes Mike Ware as saying that:
>
>
>> .... they settled on was a "polyvinyl alcohol-acetate; i.e. only
>> partially hydrolysed co-polymer, which is much more easily
>> dissolved in water than the pure alcohol. We found an 88%
>> hydrolysed PVA, with an RMM around 25 kD in 20% w/v solution, to
>> offer the best all-around results-- comparable to a 14 Baume Gum."
>>
>
> I have read, or tried to read the 5,380 posts on making gloy, or
> gloy substitute, or a gloy-like substance that accrued in the 20
> minutes I was offlist, but now I surmise from this citation that 14
> baume gum is (still) the criterion.

Judy,
Perhaps you read them too fast; I think you may be confusing a
couple of things here. I don't think Mike and his student were
trying to reproduce gloy, nor was I interested in reproducing gloy
when I asked Mike about PVA. My reason, and I assume theirs as well,
for using PVA for research into dichromated colloids, is that it has
a simple and well-understood chemical structure, so you have a better
chance of being able to tell what's going on than with, say, gum,
which has an enormously complex structure that's not completely
understood, and what's more is variable in its molecular weight, so
it wouldn't be possible to do any stoichiometric analysis with it.

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).
Katharine
Received on Wed Mar 29 20:03:10 2006