U of S | Mailing List Archive | alt-photo-process-l | Re: Stock Paint:Gum Solutions?

Re: Stock Paint:Gum Solutions?

24 Ekim 2008, Cuma, 9:41 am tarihinde, Alberto Novo yazmış:
> ...Also very confusing is parts/parts, because the units of
> such parts are not declared. Is it weight/weight, or volume/volume?
> In the first case, 1+3 leads to 25% w/w, and 1+2 leads to 33% w/w...

I always assumed that 1+2 is w/w since gum can be in various forms;
powder, tears and lumps, therefore the only logical conclusion is that
it's expressed in w/w (or w/v, since density of water is 1 g/ml, therefore
weight and volume are interchangeable - keeping the scale proportional). I
mix it 100g gum into 200ml (200g) water. The consistency is very good that
way, when using 1+1 coating solution (v/v, paint/gum+dichromate solutions)
-> in watercolor, that corresponds to fluid concentration (1:6), according
to paint amnt. in the coating solution, or creamy concentration according
to gum amnt... I guess both are fine for getting good results(!?), the
choice depending on practitioner's personal preference (and not to any
kind of technical limitation).

Of course, still, there's the problem of gum not being a defined compound
(it can change depending on source and year of harvest). Therefore I'm
interested in synthetic alternative such as PVA. I haven't find a good
source of suitable PVA, plus, I'm not completely sure which kind of PVA is
most suitable for our purposes. As soon as I figure these out (source and
type), I'll leave gum aside and use PVA as the colloid. (My current
understanding is that something like 85% hydrolized, with a molecular mass
around 10 - 12.000 should do well... Any thoughts?)