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?) Regards, Loris.
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