Re: A few gum things
Let me say first that I have zero technical knowledge or training on this topic, but I wonder whether there is any real basis for preferring glutaraldehyde over formaldehyde. Although g'de is marginally less likely to get up your nose than f'de at room temperature, it seems just as nasty in almost every other respect. At least the appalling smell of f'de prompts you to take immediate steps to protect yourself. One analysis I found on google suggests the apparent lack of carcinogenic response to g'de is due to its greater toxicity compared to f'de! Don Sweet ----- Original Message ----- From: "Christina Z. Anderson" <zphoto@montana.net> To: <alt-photo-process-l@usask.ca> Sent: Monday, April 07, 2008 8:14 AM Subject: Re: A few gum things > Wpw, Henry, > Thanks for this--I will try the extreme dilution thing asap! > > I totally agree about the yellow. I try to forbid myself from developing > the yellow layer at night because invariably I wake up the next day and the > resultant print turns out too yellow biased. If I err on any layer, it is > development of the yellow. > > LOL I have to tell you a funny. The first time I taught gum in my alt class > a la PDN, the students felt pretty bogged down with curving gum AND learning > it, and I only had 2 final projects in gum at the end of the class. The > next time I taught gum, I had one non-curved/low tech assignment in gum and > then went into gum curves and I had students who really wanted to explore > monochrome, duotone, tricolor, etc. etc.--in other words, more assignments. > > SO, this year, I assigned these assignments: one layer monochrome uncurved > gum, duotone uncurved, tricolor uncurved, tricolor curved, and then tricolor > curved over cyano. The overwhelming opinion from the students was to start > out with correct curves because when they finally got to the curved gum > prints it was infinitely easier to get a good print! > > I always learn and morph with my students....next time I will do one carbon > black uncurved monoprint and go right into curves. > > Now, some other gum things: > > Two, with offlist correspondence a gummist struggled with gum immensely, > specifically the blue layer staining horribly and/or not releasing, and > finally bit the bullet and sized with glutaraldehyde-hardened gelatin. > Presto, perfect gum print first shot. I have had this experience with a > number of offlist gummists. Photographer's Formulary now sells glut, but it > is at a 25% (!) strength so must be cut down to 2.5%! If used at 25% it > requires less than a ml of that per liter! > > I decided this fall/winter to size a bunch of paper a la formaldehyde, > because I really wanted to compare the two (glut and formalin) side by side. > Hey, formaldehyde works great. I sized my paper with gelatin inside, then > went out into my garage and hardened in a bath of 100ml formalin to a gallon > water. Hung all my papers to dry out there. When fairly dry, I brought all > the sheets inside the house and hung them in the bathroom. I was not > prepared for what happened. > > My garage was about 40 or so degrees. My bathroom was 70. The formalin > outgassed horribly, so bad that I had to slam shut the bathroom door and not > enter because my eyes stung horribly. Glut does NOT outgas at that low > temp. Another plus for glut! > > Well, it wasn't a question of not entering the bathroom again. I slammed > the door shut so hard the doorknob locked on me and I could not get the door > open even with picks and screwdrivers and wrenches so my son in law had to > come over and remove the door handle and replace it. By that time all the > outgassing was past. > Chris > > > ----- Original Message ----- > From: "Henry Rattle" <henry.rattle@ntlworld.com> > To: <alt-photo-process-l@usask.ca> > Sent: Sunday, April 06, 2008 11:41 AM > Subject: A few gum things > > > Over the past month or two, Iıve been working through the PDN process for > tricolour gum (for the second time, but this time doing it properly, and > avoiding ³shortcuts² that turned into dead ends). I really enjoyed the logic > of PDN and the way it makes you look at every step of your working > procedures, and also the fact that it actually works! > > On the way I learned a few things which most of you probably know, but might > be of some use to someone. Here they are: > > 1. Thereıs a use for that long-neglected darkroom masking frame - itıs > perfect for holding paper flat for brush coating. > > 2. Donıt develop and clear gum, especially yellow, by the light of a > low-energy compact fluorescent bulb! One evening I ³cleared² a yellow > pigment layer in a room lit by an energy-saving bulb. Next morning, by > daylight, the pigment layer was all still there! I looked up the emission > spectrum of these bulbs. There are spikes and gaps in the spectrum > everywhere - (see for example > http://beale.best.vwh.net/measure/cf-spectrum/index.html, or > http://home.freeuk.com/m.gavin/grism2.htm). These lamps emit blue, green and > red wavelengths, but in particular there is almost no yellow. I should have > known this - I studied physics - but experience is a better teacher... > > 3. The best way for me to clear a gum print in a reasonably repeatable and > controllable way is to use a gardenerıs hand-held spray-mist (thank you, > Christine!). > > 4. For tricolour prints using gum over cyanotype, Iıve found that > traditional cyanotype, used at full strength, is just too strong a colour to > balance with watercolour pigments. However it works fine if you dilute it. > Diluting 1 ml of (A+B) with between 5 and 7 ml of deionised water gives a > good medium blue. Once diluted, it needs less exposure than full-strength > (1+7 was 2 stops faster than full-strength A+B) and it also needs a > significantly different PDN curve. (Again, thanks Christine for offline > discussion). > > With best wishes > > Henry > > >
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