Re: A few gum things
I've tried it and it works fine, but in my case I am trying to reduce dichromates, so I choose glut as my primary pollutant in place of another dichromate step. Until my recent discovery of Masa, I had use gesso for over eight years. Gesso on paper (old prints_. gesso on wood, on tap paper, and primarily on aluminum. I find that bottled artist's gesso using acrylic did not have enough tooth and gum. Some stuff that came from Canada (forgot the name - white containers with red lettering) worked OK, but that the best results were to be had with using the "old formula" gesso: home made with rabbit skin glue. On Sun, Apr 6, 2008 at 11:27 PM, Diana Bloomfield <dhbloomfield@bellsouth.net> wrote: > Oh, I would like to also add that I tried that sizing suggestion in James' > book (and I saw it mentioned somewhere else, too) where you size with gum > and dichromate-- I tried that twice and couldn't get it to work. Has > anybody ever actually tried that, and does it work? > > > > > On Apr 6, 2008, at 11:16 PM, Christina Z. Anderson wrote: > > > > Don, > > Maybe this might help, a quote from Mike Ware. Also, Ryuji has posted a > lot of info in the past on glut, and he was the one who intitially led me to > use it. BTW I had not told Mike what strength I was using, and I normally > use a 2.5% solution but with the 25% that the Formulary sells, I take a ml > out of the bottle, immediately put it in a thermos of 1 liter of gelatin, > and keep that capped at all times, pouring out 1/2 c. at a time. He was > talking about 40% to 40% (or 37% as formalin is) and the most important > thing here is that formalin is a gas at room temp. I can also locate my > notes from Ryuji but he may chime in without my having to do that. > > Chris > > > > "Whence, it seems from the LD50 (lethal dose, 50% rat population) values, > > that glutaraldehyde is about six times more toxic than formaldehyde *on a > > weight basis*. This is generally born out by the recommended Occupational > > Exposure Limits, which is about four times lower for glutaraldehyde - > again, > > on a weight basis. > > > > Set against this is the fact that formaldehyde is a known carcinogen in > lab > > animals but glutaraldehyde is not known to be. > > > > Both substances are said to have "reproductive effects" i.e. may be > > teratogenic or mutagenic. (Pregnant students keep away!) > > > > But the toxicity measurement per unit weight gives you no idea of the > > relative risk in practice, which also depends on the amount of substance > > that might be ingested/absorbed/inhaled:- > > > > Let's suppose no-one is going to drink the hardener baths - that's a short > > road to a painful death. > > Let's further suppose that gloves and labcoat will always be worn and a > > face-mask if needbe with the concentrated solutions, so there is no > > possibility of skin contact with the solutions. > > > > Then the only risk comes from *inhalation of the vapours*. > > The relative risks here could be very different - and much less for > > glutaraldehyde - because of their differing physical properties. > > > > Both substances are usually supplied as 40% solutions in water (tho' you > may > > well dilute them 10x ? for use as hardeners). But this is where I run out > of > > data - I don't know the vapour pressures of these substances over their > > aqueous solutions, but they must be very different: > > > > formaldehyde (pure) is a *gas* at room temperature, Boiling Point -21 C > > > > glutaraldehyde (pure) is a rather involatile liquid, Boiling point +187 C > > > > so glutaraldehyde is far less volatile, and its solution will have a much > > lower vapour pressure over it than formaldehyde - so far less is likely to > > be inhaled. Just the 'smells' are an indicator. Sorry I can't quantify it. > > > > What I'm saying is: > > > > 1) The higher intrinsic toxicity of glutaraldehyde should not be an > argument > > for preferring formaldehyde, because you are likely to inhale much more > > formaldehyde than glutaraldehyde - so the toxic effect is comparable or > > worse. > > > > 2) Both substances are toxic enough, in concentrated solution, to require > > handling in a fume hood with an adequate air extract system." > > > > ----- Original Message ----- From: "Don Sweet" <don@sweetlegal.co.nz> > > To: <alt-photo-process-l@usask.ca> > > Sent: Sunday, April 06, 2008 7:36 PM > > Subject: 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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