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

Re: Stock Paint:Gum Solutions?

I have been using Mowiol on/off the last couple weeks. The 8-88
variety recommended by Mr Jeanlis was sold out at Kremer's so I used
4-88  (310grs per litre of water). I don't know if I will be using it
much in the future, it reacts differently than gum of course. It seems
to be slower than gum : MY exposure times for gum are between 2 and
3:30 mins, Mowiol needs 7 to 10 mins exposure. It seems to dry slower
and requires some heat to loose it's tackiness. What I do like is the
fact that a mixture of Mowiol, paint and pot dichromat does not seem
to get bad, even after 2 weeks.

2008/10/24 Loris Medici <mail@loris.medici.name>:
> 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.