Re: A few gum things
Thanks, Keith. I have no idea what I did wrong-- followed the steps
to the letter with the gum/dichromate sizing, but you are correct--
reducing the use of dichromate is certainly preferable. I was
actually trying to get away from gelatin as I just don't like what it
does to the surface of the paper. Since then, I tried less gelatin
and it looks better and still seems to work fine.
Thanks about the gesso information, too.
Diana
On Apr 7, 2008, at 10:11 AM, Keith Gerling wrote:
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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