Here is my Ferric Ammonium Citrate puzzle:
Early in the semester we mixed cyanotype from a partly-used bottle of
ferric ammonium citrate, which I shall call lot #1. I supervised mixing at
first in the morning class, then let students mix on their own. We made
many prints, all fine.
In the afternoon class, the last of lot #1 was used up and another
container of fe am cit from a later delivery, which I shall call lot #2,
was opened. Students mixed as before and we made many prints, all fine --
although I realized later we were printing with emulsion mixed in the AM.
Nor did I check the appearance of solution being made from lot #2.
The following week several students from the afternoon class revealed that
their cyanotypes printed during the week had not "come out." After some
head-scratching we realized all failures were from lot #2. The powder
looked fine, like ordinary green scales, but mixed into distilled water, I
now discovered, it immediately turned a dark brownish blue-green -- not
the usual light green. (This was just the fe am cit in distilled water,
before adding potassium ferricyanide.) The bad prints were very pale and
foggy, even after half-hour exposures (usual is 6-9 minutes).
Luckily I found one last bottle of lot #1 in the closet. We shipped the
bad lot #2 back to Amend, which replaced it with a different batch, which
I will call lot #3.
No further fe am cit incident until we got to van dyke brown. We began VDB
with the tag end of that last lot #1 bottle -- all OK, the usual light
green. Then we opened the first lot #3 bottle. Uh Oh! Dark brown
blue-green. Let's not risk silver nitrate in bad chemical, I said. There
are no more over-the-counter chemical stores in NYC, but I had a nearly
full bottle of ferric ammonium citrate (part of lot #1) at home. That
night I mixed a little with an ounce of distilled water to show the light
green colo r it's supposed to be & brought chemical & water to a student
living nearby who brought it to school next day & mixed his vandyke brown
with it. (I'm there Mondays only.)
Uh oh, again! When he mixed my chemical with distilled water it turned the
same dark green-brown as lot # 3. Or he said it did, I didn't see it.
Student, however, went on to mix it with his silver nitrate & tartaric
acid to make vandyke brown. Printed fine, he said.
So the next week -- this past Monday -- I took a bottle of lot #3 home
with me and mixed it with my distilled water, thinking maybe all ferric
ammonium citrate is light green in what is, after all, Greenwich Village.
No. It mixed up the same "bad" dark brownish-green as it had in Brooklyn.
So now I have to decide -- to send lot #3 back because it mixed up a bad
color, or keep it because my good lot #1 mixed up the same "bad" color" at
school, or the student thinks it did.
If I hadn't seen the failed cyanotypes from lot #2, I wouldn't have
worried so much about the dark solution. (Is this perfectly clear?) We'll
have enough of my lot #1 to see us through the semester, which ends week
after next. I'll mix up a small batch of VDB with lot #3 next week to see
for myself. But if someone out there (still reading, and getting the
numbers straight) has an idea, I promised to "ask the list."
The questions for Dr. Science are:
1. Why did lot #1 turn dark in the distilled water at school but not in my
distilled water at home?
2. Is there any other test I can apply to lot #3 before either mixing it
with the silver nitrate or sending it back?
PS: A while ago, here at home, I mixed some ferric ammonium citrate for
cyanotype that looked light green in the distilled water, but as soon as I
added the potassium ferricyanide it turned darkest total blue. At the
time, Mike Ware was on the list, and he prescribed a certain % of
ammonium dichromate to add to cure the badness, which I did. The cyanotype
then mixed up without precipitation and made a print -- but was so slow
and contrasty, I threw out the chemical anyway. This isn't the same
thing, since solution goes blue before anything is added, and not so
intense.
Blue and boohoo,
Judy