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

Re: Stock Paint:Gum Solutions?

This discussion about baume, concentration etc. periodically returns on the list. I myself have had some difficulties the first time I started printing gum, because very often the concentration is expressed in a fake percentage, like 30% for a mix made from 30 g of gum plus 100 mL of water. For me, as a chemist, this was very puzzling because this is not 30% but 30/(30+100)= 23% weight/weight. 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.
Dirk-Jan: your 30% gum, which is for me a 23% w/w, is very close to Kees' 1+3 (if both parts are weights, it is my 25%) and the respective Baume degrees are quite consistent.
Hi Kees (and others),
When you're tired of converting the hydrometer results to baumé:
in the better cooking shops, you can find baumé meters that are used for
measuring the syruppy of sugar-melts/caramel kind of mix..
I bought mine for about 7 euro's :-)
My 30% gum solution (30 grams gumbrick dissolved into 100 ml distilled
water) turned out to be 13 baumé

2008/10/23 Kees Brandenburg <ctb@zeelandnet.nl>
Hi Marek,
That's a bit confusing. When I measured my former mix (1 part gum + 3 parts
water) some year ago when Chris asked us about our gum mixes it turned out
to be near 14 baumé. Now I use a heavier 1 part gum + 2 parts water mix.
As I have both concentrations at hand I just (re)measured both mixes with
my simple winemakers hydrometer.
these are the results:
My 1+3 mix has a specific gravity of 1.101 this is 13,3 baumé
My 1+2 mix has a specific gravity of 1.132 this is 16,9 baumé
You can lookup the baumé grades here:
And some pictures from the lab:

On 23 okt 2008, at 16:40, Marek Matusz wrote:
I use 14 baume ready gum solutions (about 30% as I recall), so it is the
same as yours 1:2.