Re: Making Ferric Oxalate from Scratch


On Tue, Nov 17, 2020 at 04:21 AM, Pfriedrichsen wrote:
In regards to lactate, some time ago I made some ferric ammonium lactate (FAL) using precipitated ferric hydrate ...  Here is the unusual outcome: The prints are deep but have a muted violet hue ...  if this finished print is placed in bright light like sunlight, and the print is left to recover, the violet hue is lost and the colour reverts to a more traditional cyanotype hue.
That's very interesting, Peter.
I'm wondering if there is a way to change the title of a thread on this new server - say, to "Ferric lactate sensitizers" Advice anyone?
I seem to have led us away from Niranjan's original ferric oxalate question...

Do you know the stoichiometry of your FAL complex?
Regarding your violet coloured cyanotype and its reversion, one sees the same behaviour with ammonia vapour: here is a quote from my Cyanomicon §8.1, p.261:

Exposure just to ammonia vapour, rather than solution, does not fully

hydrolyse the Prussian blue but imparts to it an impermanent, though

striking, violet colour; this toning is reversible within a few hours simply

by restoring the print to air, when the occluded ammonia gas is

presumably lost, and the pigment reverts to its original blue colour.

It is conjectured that this effect may be due to ammonia causing a

reversible deprotonation of water coordinated to Fe(III) in the PB lattice;

transformation of the ligands from OH2 to OH- would affect the

energy of the electron charge-transfer transition between Fe(III) and

Fe(II), and change the colour.

Perhaps your resulting print contains some free NH3?

Mike Ware

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