| Ferric
Oxalate
its care and feeding
Bostick & Sullivan is the only manufacturer
in the world today making powdered ferric oxalate. We have made
a highly consistent product for over 17 years. We do not make a
liquid grade and dry it down, but it is made as a precipitate, then
filtered and dried.
Dry powder ferric oxalate has a very long shelf
life. I still have some that I made in 1984 and it is still bright
yellow green and in perfect condition. Many top printers depend
on this consistency. Several times I have made "improvements"
to this product and then to have the phone ring off the hook with
"complaints."
Some of the best platinum printers in the world
today use our powdered version and make perfect prints. Some printers
make some modifications to the base product, others use it straight.
Seventeen years of experience have taught us that there is no universal
magic witches brew ferric oxalate. The best magic we can see is
for the ferric oxalate to be stable and consistent from batch to
batch and then let the printers make their own modifications to
it if they wish.
Powdered ferric oxalate will last a long time
and can be quickly put into solution. Here are some of the things
that some printers do with it after it is put into solution:
| 1.) |
Add hydrogen peroxide to it.
This will clear up any slight content of ferrous oxalate to
ferric oxalate, and will act as a long term preservative. Some
outgassing may occur with the use of peroxide, and vented cone
caps should be used so the bottles do not explode. Though we
have heard of no reports of this happening, we don't add peroxide
to our liquid grade products because of this slight risk. We
will be doing more assessment on this in the future. Some printers
use hydrogen peroxide in the developer or emulsion as a means
of contrast control which is another reason we don't add it.
Our powdered product will last over 10 years and we produce
dry packs, so the longevity issue is a minor one with most printers |
| 2.) |
Add oxalic acid to it. This will slow
it down and increase contrast a bit in most cases, these things
depend a lot on personal variables. Our dry grade has a small
quantity of free oxalic acid already in it. One of the "improvements"
I tried to make was to remove this free oxalic acid. Was I wrong.
When oxalic acid is added the color goes from yellow brown to
yellow to green. Some printers add as much as 15 grams of oxalic
acid per 100 ml of 27% ferric oxalate solution. |
| 3.) |
Add an emulsifier, surfactant, wetting
or spreading agents to it. These can be gum Arabic, poly vinyl
alcohol, Tween 20, (Tweens 40,60,80 work as well). These will
alter the spreading and absorption qualities of the material. |
| 4.) |
Add lead oxalate or lead citrate, or lead
nitrate to it. Add cadmium compounds. Add mercuric compounds.
These compounds are dangerous and should only be dealt with
by advanced and trained printers. |
Dick Sullivan
Notes:
David Kennedy relays this tip to us. He and John Rudiak have been
experimenting and say that the following formula will increase the
speed of the ferric oxalate without any degradation.
To 100 gm of liquid for add 18 gm oxalic 6 gm edta
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