Re: A few gum things
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.
"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
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" <email@example.com>
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
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!
----- Original Message ----- From: "Christina Z. Anderson" <firstname.lastname@example.org>
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
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
a la PDN, the students felt pretty bogged down with curving gum AND
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
then went into gum curves and I had students who really wanted to explore monochrome, duotone, tricolor, etc. etc.--in other words, more
SO, this year, I assigned these assignments: one layer monochrome
gum, duotone uncurved, tricolor uncurved, tricolor curved, and then
curved over cyano. The overwhelming opinion from the students was to
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
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
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
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
water. Hung all my papers to dry out there. When fairly dry, I brought
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
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
open even with picks and screwdrivers and wrenches so my son in law had to
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
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
red wavelengths, but in particular there is almost no yellow. I should
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
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