Re: A PVA for printing "gum" : a practical approach

Chris, there's little to disagree with below, about gum printing.
But what does any of it have to do with PVA, which since you have
retained it in the subject line that you have otherwise altered, I
assume you must think it has something to do with?

My point, and Ryuji's, I think, was that PVAs vary on several
parameters, and just because one PVA works fine mixed with glycerine
and water to approximate gloy, that doesn't mean every PVA will. PVA
doesn't work like gum, where it's just a matter of adding more or
less water to get the viscosity and the printing properties you want.
You have to start with an appropriate PVA in the first place, which
is why Mike Ware and his student took some time to determine what
that "right" PVA would be to approximate the printing characteristics
of a 14 Baume gum, before proceeding with the research question. For
example, if you get a PVA that's not hydrolyzed enough (too much
toward the "acetate" end of the PVA continuum) then it's not going
to be soluble when coated and dried and therefore wouldn't work in a
dichromated colloid process. And if Mike's quote is correct, if it's
too hydrolyzed, then it may be hard to mix with water. And by the
same token you need to pay attention to the degree of polymerization.

It reminds me of a time when I was having trouble printing on glass,
and someone here suggested silane as a sub. So I ordered some silane
and tried it, and it didn't work, and I reported that back here.
Then someone cheerfully said, well, then you probably got the wrong
silane--there are about a thousand of them and they all do different
things. At that point I said, life is too short! I was trying to
print on glass for an upcoming show, and I just simply didn't have
time to do trial and error with silanes, never mind the expense, so I
figured out a different way to print gum on glass. But it would have
been helpful if someone could have pointed me immediately to the
"right" silane for the purpose.

So I thought it might be helpful, when Loris asked what PVA to use,
to share what I know about what PVA might work best. I don't think
this is being particularly pointy-headed. From what I've read of
Terry's description, and this could of course be incomplete because I
don't see all of his posts, it sounded like he just happened to have
some PVA on hand and it happened to work. But to conclude from this
lucky happenstance that if this PVA worked, then surely all PVAs must
work the same way, is quite a reach.
Katharine

On Mar 30, 2006, at 5:49 AM, Christina Z. Anderson wrote:

> Terry said:
>
>
>>> I started with a heavier gum and found that the printers' 14 gum
>>> was too thin
>>>
> for me. I tried a gallon of the printers' 14 but passed it on to
> someone else
> even before I discovered Gloy all those years ago. I prefer the
> 17 but
> that does not make the 14 wrong.
>
>
>>> The result is that when I mix up PVA and glycerine for my gum
>>> prints I aim to
>>>
> achieve the same consistency as that of Gloy or the gum I
> preferred, but that
> is my choice.
>
>
> Hmmm....Terry, I must be missing something so I'll appear really
> stupid and ask it anyway: is there anything wrong with plopping in
> some gum arabic powder into the "too thin" gallon of gum arabic to
> make it thicker? And then when that gallon is used up, just start
> mixing your own from scratch anyway? I'm never one to waste a
> gallon of that stuff...
>
> I always do that because I agree that most commercial gums are a
> bit thin. I usually mix a batch of gum arabic at 1+1 or 1+2 and use
> a dash of the thicker stuff in the mix if I'm using up a bottle of
> commercial.
>
> All the hoopla about gum being hard to mix up, or needing a certain
> baume, in my practice, is a waste of time, literally. I whip it up
> in a blender and use it immediately, kitchen measurements. I
> figured if all the oldies did the 2 in 5 or 2 in 4 there must have
> been something to it.
>
> But, whatever floats your boat-er-baume meter.
>
> But there's nothing better than having 15 students in a semester
> prove your method right, and if there's anything missing from your
> method, they'll sure find it :)
>
> Speaking of which, 15 students have successfully hardened with
> glutaraldehyde, successfully made tricolor gums with very saturated
> colors, with nary a stain.
>
> Their biggest problem, IMHO, is learning how to "Zen" it....not to
> rush, not to opt automatically for the hair dryer, the spray
> bottle, the brush...next time I will NOT teach the shortcuts right
> away. I had a number of them hair drying the layers immediately
> before and after development so they could do a tricolor gum print
> in a couple hours! I mean, that's fine and dandy in their own
> home, but in a squunched alt process lab with 15 students vying for
> space, hair dryers going all the time...where's the pleasure? Oh
> how I digress, obviously this is fresh in my mind...
> Chris
>
>
Received on Thu Mar 30 11:03:14 2006