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

Re: Stock Paint:Gum Solutions?

DJ et al,
This whole thing used to confuse me so much until one book from early 1900s addressed the fact that a "30%" gum solution (meaning 300g gum + 1000 ml water but sometimes some authors meant 300g in a total volume of 1000ml) wasn't truly 30%.  Then I went to just the "practical" or "cooking" method of worrying about gum printing--e.g. "2 in 5" and whatnot.
And this is why I would like that -at least in these cases- the percentage were not used but a different, universally understandable and less confusing notation like for example the ratio (e.g. 1:2, 1+3, "2 in 5", etc.).
But DJ brings up a great point--the people who measured pigment by weight.  Pigments vary so much by weight, and a lot of time the weaker pigments (e.g cerulean blue) weigh a ton and the stronger pigments (e.g. thalo) weigh very little.  Like comparing the weight of ground up rock to the weight of a vat dye.  I found that a light pigment weighed 5g and a heavy 9 g. given the same volume, and weight did NOT correspond to covering power or saturation.  So I quit using weight as a form of measurement as well.
And this is why the term "part", if not followed by the measure unit (weight, volume, etc.) may be confusing.
About the use of "tube" as a measure unit... Who knows what is -and in what proportion- in a tube other than pigment, water and (if possible) gum arabic? This means that comparing tubes to tubes is almost insignificant unless for the same pigment and the same brand.