U of S | Mailing List Archive | alt-photo-process-l | Re: variables in gum (was Re: greens in gum)

Re: variables in gum (was Re: greens in gum)

On Oct 1, 2006, at 2:02 PM, Tom Sobota wrote:

My dry green pigments are from Maimeri. Viridian green, which has been brought to my attention by Christine some time ago, is an easy color to work with, and not staining at all. Not much covering power either. Maimeri sells it as 'verde smeraldo' PG18 and it is a hydrated chrome oxide. BTW it doesn't seem to react with the dichromates at all.
That myth just doesn't want to die, see


Phthalocianine green mixed in small quantities with viridian makes a nice strong covering green.
This is a good idea, since viridian is a weak pigment and pthalo very strong; the pthalo will add some body to the viridian.

I don't find that any specific pigments stain, green or any other color, but the discussion of the last few days makes me very aware of how little use any of our observations are to any of the rest of us, except that I do think that in the aggregate, all of our observations added together will eventually help us to a better understanding of how gum works.

Judy Seigel wrote:

On Sat, 30 Sep 2006, John Brewer wrote:

I remember reading in a book somewhere that greens are more likely to stain and should be made from yellow and blue. I've not had a stain problem with greens. One of those gum old wives tales I guess. Here's recent gum over cyanotype http://tinyurl.com/ ly3bb using DVP 277 sap green (PG7 and PY 42).

Hi John,
Isn't there another expression besides "old wives tale", something arguably more politically correct? How about old boys' something or other... Actually I think there isn't, probably for lack of trying. (There's an expression something like bubba meisser, but I think that means old wife too.)
Meanwhile, I agree about green, whoever told the tale. I've found that thalo green clears as well as thalo blue, which clears as well as anything I use when other conditions are right, but I usually use the blue with another color to make green anyway, as it producs a richer tone. (Tho I have used thalo green for its covering strength, much greater than for instance viridian, tho I suspect that tubes labeled viridian may now be thalo... my book giving the specifics has been stolen by -- I suspect a surreptitious visit from the list... I mean why else would my Kosar AND my pigment book BOTH disappear around the same time? )
As for the apparently inconclusive considerations of variations of temperature & humidity and/or relative humidity in gum exposure, let me suggest that other variables affect the effects as well, which would explain the lack of consensus. We have in fact agreed that results in gum printing depend on a *combination* of variables, so it seems unlikely that exposure/development variables would respond to only two. My own guess (and extrapolating from casual observation and anecdotal "evidence") is that developing water, the gum arabic and particular pigment(s) affect results as they see fit, making "principles" involving only two conditions in isolation dubious.
Theoretically, one practitioner's results in his/her studio, using same everything for comparison tests should be more indicative -- but I wonder how perfect any such tests can be, without true "rocket science" lab conditions-- at least not in, for instance, urban locations. For instance (a very small instance, but a good warning) I found that a particular gum arabic that was unusable in my studio worked fine at school with same everything (paper & paint) but *Brooklyn* water (or that was the only variable I could think of -- could have been I suppose the cigarette smoke in the air).
I've played this game with other printers, exchanging gums & papers & using paints from same lot, etc., with some totally opposite results (eg, stained badly vs. cleared, etc.). In my own practice these systems have less importance, because I don't do a standard development OR exposure, rather making a ball park exposure time (according to mix, negative, requirements of print & atmospheric conditions) then developing ad hoc -- by eye. My feeling also is, how do I know what I want until I see it? Or, as the extremely old lady said when her children asked what funeral arrangements she wanted, "Surprise me").
And one other thing... my guess & experience is that even if you suss out all the variables for your particular set up, some are beyond your control -- unless you develop in distilled water & maybe even then. At least here in NYC the water changes by the season, by the weather (including what sediment the winds stirred up in the Catskills that week) AND, what the boys in the pumphouse (maybe even a few girls) decided to add that day. They also vary additives by season... and (according to the literature in small print they send along with my water bill) "conditions."