Re: polivinyl alcohol vs. gelatin sizing

Giovanni Di Mase wrote:
>
> Thanks Katharine.
> You just spare me to test that.
> What about using PVA alcohol or acetate for sizing?
> In my case I was able to have bot chemicals separated and not confused but I
> am trying to figure out which one is good for what.
> Kevin said to me that the acetate works for sizing and he uses but that was
> it, I haven't get any further info.

Hi Giovanni,

If you use polyvinyl alcohol for sizing, it's going to dissolve in the
non-image areas on the first introduction to water. So, assuming you're
printing gum, if you print more than one layer you're not going to have
sizing on those areas for the subsequent coatings, which depending on
the paper could result in pigment staining in those areas.

So my recommendation would be that if you're going to use one of them,
then use the acetate. Or just use Elmer's Glue. I don't know what's in
it; I've always assumed it was mostly polyvinyl alcohol, but it can't be
entirely because I don't think it dissolves in water once it's dry.

 It still seems to me that acrylic medium would not only be easier to
use but easier to find, and would produce a similar sizing feel at the
same dilution, but I haven't ever used the other stuff and for all I
know it may be that the difference between them is greater in effect
than I'm imagining. I just haven't ever got an answer to that question,
why the PVA/Elmer's Glue rather than acrylic medium.

  The only trick about acrylic medium is that most people (including me
in the beginning) think that you'd use matte medium, assuming that the
gloss would give you a glossy surface; this is wrong. The matte medium
has waxy stuff added to kill the gloss, that makes the size less
hospitable to gum. It's the gloss medium that works best, and at the
dilutions that work best for sizing (1:10 or so) it doesn't make the
paper shiny at all.

Katharine

> Giovanni
>
> ----- Original Message -----
> From: "Katharine Thayer" <kthayer@pacifier.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Sunday, July 31, 2005 4:55 AM
> Subject: Re: polivinyl alcohol vs. gelatin sizing
>
> > Ryuji Suzuki wrote:
> > >
> > > From: Giovanni Di Mase <gdimase@hotmail.com>
> > > Subject: Re: polivinyl alcohol vs. gelatin sizing
> > > Date: Sat, 30 Jul 2005 16:28:30 -0400
> > >
> > > > Let's be very clear, which one is Elmer's glue made from?
> > >
> > > The main ingredient is poly(vinyl acetate) and water.
> > >
> > > > When you said PVA is acetate or alcohol?
> > >
> > > PVA is an ambiguous acronym. Some people use PVOH to indicate
> > > poly(vinyl alcohol) to avoid confusion.
> > >
> > > > Yes, there is a confusion between them.
> > >
> > > There is no confusion in terms of chemistry. The confusion is just in
> > > acronyms. It's also that vinyl acetate and vinyl alcohol are often
> > > used as copolymers and also as mixtures of multiple copolymers in
> > > practice to achieve desired properties. One example I gave was acrylic
> > > medium.
> >
> > Perhaps, but in practice, which is what I think we're talking about
> > here, they behave very differently. You can use polyvinyl alcohol as the
> > colloid in the gum process. You can't use polyvinyl acetate or acrylic
> > to print gum with, as neither of them will dissolve once dry, and the
> > polyvinyl acetate won't mix with the dichromate; it just precipitates
> > into little clumps of gunk. (I found this out once when I bought
> > something called PVA glue, assuming it was polyvinyl alcohol). So it
> > doesn't make sense in terms of practice to talk about them as if they
> > were interchangeable.
> > Katharine Thayer
> >
Received on Sun Jul 31 11:00:51 2005