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

I changed the subject line as we seem to be becoming somewhat theoretical
when what we need is practical advice. Earlier someone had changed ir from 'New
Gloy=bakerex' which I rather liked.

My practical advice is that it does not much matter which PVAs one uses. Try
some, see what happens.

As I said, did all that research, more than 300 exchanges forsooth, come up
with any answers.

Terry

In a message dated 30/3/06 6:04:51 pm, kthayer@pacifier.com writes:

> 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
>
Received on Thu Mar 30 11:32:56 2006