Re: ferri sesquichlorati
Halvor,
This is really fascinating...
First of all, I found the quote: "...earlier observations by Alphonse
Poitevin in 1863, that ferric salts cause gum and similar colloids to harden
and become insoluble in water, whereas ferrous salts do not." p. 53 Ware,
Cyanotype.
I had heard this once before on the list--I think Judy brought it up a long
while back--and thought it an interesting phenomenon, but didn't know where
it came from until you brought it up.
I dunno, might just try mixing a bit of A and B and plopping it in my gum
solution as per normal--it'd have the dichromate in it to harden, and the
cyanotype would just get exposed at the same time? Might be worth a try. I
never thought about this until China Hamilton talked about adding the silver
nitrate to the mix--a dichromatype he called it.
Chris
But; first I did probably only do a few attempts with gum, with no result,
that was mixing ferric chloride and tartaric acid in a ratio to make
ferric
tartrate, as I can remember it right now, (that also means I did not
follow
the recipe properly) this is about one year ago. With gelatine that gave
the
result in the link I sent. With gum nothing. It is very possible that
different concentrations than what I used would have given better results
for gum (and for the gel :-).
I did several attempts with gelatine, got good edge sharpness but the
surfaces where quite uneven, sort of woolly. Possibly thinner layers would
work better, but contrast might be high, believe this process, as the
pellet
process, was used for line drawings and copies. This might be possible to
adjust with pigment concentrations or otherwise ...
If you have Mike Wares Cyanotype book, have a look on the pellet process.
It
contains gum, ferric and tartaric acid. It is mentioned somewhere in there
that Prussian blue can harden colloids, but have again not found any
closer
explanations. For gelatine normal cyanotype "hardens" gelatine in thinner
layers, but I had less success with thicker layers. (A cyanotype mix in
gelatine makes a very thin relief on glass for example, but seems like the
gel need to hang onto something in addition, not too strong hardening).
How
does a normal cyanotype solution mixed in gum arabic work btw ? I have not
tried this..
In my experience it is particularly the tartaric acid that makes this
works
in a "positive manner" - the exposed areas becoming soluble, as mentioned
something like this happened when mixing in tartaric acid + AFC in
gelatine. It does not happen if mixing in citric acid or "long list of
other
acids" + AFC in gel, have not tried that with other ferric salts.
______________
some guesses on this.. (and I am not really a chemist so please suggest
things anyone..)
Fe3+ could, maybe, crosslink, same as cr3+ ... On exposure link breaks,
problem is that then the ferrous could be a stronger cross-linker than the
ferric. Which is when the tartaric acid could come inn and link up with
the
ferrous in competition with the gel - maybe. Easy to check, does FeCl
harden
gel ?
Or the tartaric acid alone crosslink's the gel, on exposure it is oxidised
by the ferric going to ferrous and the link breaks ... Easy to check, does
tartaric acid harden gel ? :-)
It is possible that ferric tartrate crosslink's the gel and hardens it,
(sort of; gel-tartaric-Fe-tartaric-gel) on exposure the link breaks and
the
gel becomes water-soluble... Ratios given in the recipe I looked at did
not
match making ferric tartrate out of the all the ferric chloride, but the
recipe I looked at was old and so on... Should be possible to try some
tests..
Have not had time to play with this, maybe next life, or in some weeks,
but
are, obviously, interested..
______________
The last chapter in "The American Carbon Manual" : HISTORICAL NOTES ON
CARBON PRINTING. Have several descriptions of this method, for example:
(If you don't have it, there is a word file somewhere.. Or I can mail
it..)
"The first results of this process were shown to the French Photographic
Society, in July, 1860, the process having been patented the month
previously. The details were published in the following November.* In this
process a mixture of perchloride of iron and tar-taric acid, ten parts of
the former to four of the latter, dissolved in one hundred parts of water,
is the sensitive preparation. It is poured on a plate of glass which has
been previously coated with collodion or other suitable material; it is
then
left to dry in the dark, and becomes spontaneously insoluble. Submitted to
the action of light, however, it again becomes hygroscopic."
Goes on to describe what is a "dusting on process"..
________
Seems like I just wrote most of the basis for that "summary" :-)
On 10/18/06 9:43 PM, "Christina Z. Anderson" <zphoto@montana.net> wrote:
You all are great!
OK, so here is what it says:
Photo American, 1903, A Gum Bichromate Modification:
Dr. Lux has written about this in the Deutsche Photographen Zeitung.
Paper coated with a 12% hard gelatin containing "some acetic acid and
some
iron solution", the liquor ferri sesquichlorati (as you say, below) of
pharmaceutical lore. It is added until the color of the mixture is such
that a layer 2 mm thick makes white paper look distinctly yellow.
Pigment
then added as usual. Coating done thick and even at 112 degrees F.
Expose
and develop as soon as dry. Develop in dark in water til soluble iron
salts
are removed, and then do rest of gum print in light.
Now, of course, he says "gum or other colloid" and proceeds to talk about
gelatin...
That's about it, and not very clear for sure!
I have also somwhere a person's process who uses silver nitrate in the
gum.
But Halvor, it sounds like the same in Silver Sunbeam, which I have, so
I'll
check it out, and you say no luck with it...interesting. But I did
think,
one day, when accidentally using my cyano brush to brush a gum layer on,
what would happen when it was mixed into the layer?
No mention of dichromate in this mix, though? Weird. Does the ferric
chloride harden the gelatin?
Chris
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