[alt-photo] Re: I know, another sizing question

[Peter Friedrichsen]

My results with Elmers PVAc have been 
unsuccessful since,as Loris points out, it will 
not resist water and will fail as a size.

I did some digging some time ago (an earlier 
post) and found that the Gamblin PVAc is a 
chemically modified beast that greatly improves 
water resistance of standard PVAc, so it works. 
Trial and error runs from paint/hardware store 
products may eventually yield success as Loris 
has found, but even if you luck upon the right 
PVAc type, you still have to deal with the 
unknowns of the ageing of a sizing from a product 
with unknown composition and pH.

Re Casein as size

I haven't used it as a size but I do know it will 
form a  very water resistant coating once 
hardened with Glyoxal or Formaldehyde. These 
hardened films are a little more brittle than 
gelatin films, and the films forma mat finish 
with may provide more tooth good or bad.

I think if you had a source of sodium caseinate 
powder, then it may be worth experimenting, but 
to precipitate the casein from skim milk every 
time you need to size would be more effort than 
it is worth unless there were some clear 
advantages in terms of performance or 
convenience. The only clear advantage I can see 
off the top is that the caseinate solution is 
liquid at room temperature and avoids the warming step of gelatin sizing.

Re whey

As was mentioned, the whey (clear solution) that 
is left over after the casein is filtered out 
also contains hardenable protein but it is mixed 
with lots of lactose and other impurities. I know 
you can purchase purified whey protein isolate 
which is used in foodstuffs and as a body 
building powder. From what I understand it 
suffers from poor adhesion and forms a film that 
is brittle and flaky but I have never tried this 
as a sizing.  It does have the advantage that it 
is very soluble in water and you can make 50% 
solutions without too much viscosity.-kind of like gum arabic in this regard.

Peter Friedrichsen

At 06:14 AM 09/10/2010, you wrote:
>If I'm not mistaking, Elmer's glue was used in 
>place of gum or something - that means it isn't 
>waterproof; something good for a gum 
>replacement, but not good for being able to used 
>as a sizing... As I said before, you should look 
>for something that is PVAc based, clear (when 
>dried as a film) and waterproof. See hardware / 
>paint stores, I buy mine from a paint store, 
>dilute it 1+4 and use - paper's ready when dry, 
>and the sizing is very robust; I had a student 
>put 9 layers w/o any staining... Regards, Loris. 
>2010/9/10 Trevor Cunningham 
><trevor at chalkjockeys.com>: > Â Maybe not? I read 
>in the manufacturer's details that it has a pH 
>of 4.7...I > know the Gamblin product (which I 
>can't get) is pH neutral. Would diluting > the 
>glue with distilled water help to raise this 
>number a little? Mix a > little baking soda into 
>the solution? > > On 9/10/10 9:25 AM, Trevor 
>Cunningham wrote: >> >> Â Is good old fashioned 
>Elmer's school glue a suitable PVA glue? That I 
>can >> find. 
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