Hans & Chia wrote:
Hi All
We have been making gum prints since 1984. The last 10 years we have made
our gum solutions from lumps. Today a very odd thing happened. As we were
going to test a new supplier we made two different solutions. With the new
supplier everything went well but with the one that we have used before an
odd thing happened. When the gum lumps (from Sudan) were almost solved the
solution became very thick, like tough glue and even if we added more water
than we usually use it is still like snot and has now become more viscous.
Last two weeks we teached gum in a school. The gum lumps were in a bag in
the same room where we sized the papers and hardened them with glyoxal
(using glyoxal for the first time in our alt-photo life.) We had two paper
sizing sessions. The first time when we hardened the papers we noticed a
little irritation but far from the problems with formaldehyde. The second
time the students made it themselves and they were "complaining" over the
smell of the glyoxal, telling almost the same problems one gets from
formaldehyde.
Just before we went to this school we made one liter of gum solution,
tested it and it worked very good and also kept that way (no snot!) during
the first week. The last days during the course we made more solutions for
the students so they can continue themselves. The gum solution was tough
like glue!!! We could not find any answer there (rumours said that the
students had put too much glyoxal in the solution). But today, at home,
with the lumps that were left over from the teaching session the same thing
happened again!!!
Now we are wondering: What has happened? Has the glyoxal something to do
with it? Shall we throw away the lumps we still have?
Hans & Chia
Dick Sullivan replied
Gum is quite a variable substance. I have a rather long and interesting
paper on gum Arabic on my web site that came from the Sudanese government.
It may be the Glyoxal is reacting with something in the old gum. You don't
say how you are dissolving this stuff and my experience was that it would
often ferment. If you add the Glyoxal when you are dissolving the gum then
it might not ferment, but then that may have caused problems, especially if
you are dissolving lumps in a muslin or cheesecloth bag. I prefer to
dissolve powder in a blender by slowly adding it to cold water while it is
whirring, you can make it thick enough to walk on Use a high quality food
grade gum, some grades will kick out enough dirt to start a garden.
Glyoxal is not foolproof and it does have a slight odour, but it is a far
cry from formaldehyde!
Dick<<
>>Hans & Chia replied
We dissolve the gum lumps in boiled but cooled (20C) water and when all
lumps are dissolved we strain it, check the Baume and then we add
formaldehyde. The gum we used was the best we have found during the years.
Bright lumps and when in solution still very transparent. This time we
wanted to try Glyoxal but we did not get the chance....
The only difference this time was that "Glyoxal was in the air". The gum
lumps were placed in a brown paper bag in another bag 5-7 meters away from
the sizing tray!
From: TERRY KING <KINGNAPOLEONPHOTO replied
>>Hans
>>In the days, at least ten years ago, that I used gum arabic for making gum
prints, I always placed the gum arabic in cold water and allowed it to
dissolve over a couple of days without stirring or heating. I would
certainly never have dreamt of adding a hardener to the gum and I still
cannot see what purpose it serves as perfectly good gum prints can be
obtained without doing so.
Cold water and no hardener would seem to be the answer.
Terry King<<
This has the making of a good thread, whilst hating to contradict my old
friend Terry
[in any case who would dare :-)] neither Hans or Dick said anything about
heating
the gum solution only boiling and cooling the original water. I have found
by independent research that you cannot harden gum with formaldehyde! and
here
Dicks point about fermentation has relevance ,the addition of a small
amount of formaldehyde! actually seems to preserve the gum solution, so
that no acidification
takes place. I cant make the same claim for Glyoxal, as I have not tried it
out yet, but
it could be different to formaldehyde, as gum is to gelatin, each colloid
has its own
distinctly different nature, as I tell my students add ad nauseam [ if you
wont to be the best you have to test ] .
Another good point made by Dick is his referral to the Use of high quality
food grade gum, instead of the sometimes dubious quality of third world
natural products as he says, some grades will kick out enough dirt to start
a garden.Another digression is that there must be a great amount of
parallel food technology out there, which we alternative worker's could tap
into, all those jellys,sauces, rouse, custards, mayonnaise, souffles
cre'mes,glazes,soups, and many others all waiting to be deliciously
poisoned by the addition of the salts of chromic acid.
Yes I know it is all very sad !
pete
Ps it is nice to read good old Anglo Saxon again to describe the errant
gum, rather than terms such as Nasal bodily fluids