Excess Oxalic acid in Ferric Oxalate

[Jorge]

Well, I made a mistake that seems to have some good consequences. I was making fresh Ferric Oxalate to make some prints, and I made a mistake and added twice as much as I should have.

The resulting prints with this Ferric Oxalate solution are noticeably cooler and with higher contrast that usual. Anybody has seen this before?

 

[Thomassauerwein]

Makes sense that that would happen, never thought to try it though. Course you could warm it back up with some palladium but there goes your contrast.

 

[Michael Mutmansky]

Jorge,

The increased oxalic acid may also increase your printing speed.

I haven't made direct comparisons for color, but I think that the excess Oxalic acid will be beneficial for several purposes. It will help eliminate any carbonate in the paper that might reduce the tonality of the final print. It will also help make the print clear easier after development.

I'm sure there is a point where the benefits are compromised by some other drawback, but making a subtle change in the formula in this manner may make your life easier.

I typically use more EDTA in the FO mix than is called for in the books for a similar reason.


---Michael

 

[Jorge]

Thomas, even with pure PD the prints look cooler, I dont like it!!!!

MIchael, Ah ok......at least I am notr seeing things..

 

[wmlaven]

Jorge,

The increased oxalic acid may also increase your printing speed.

I haven't made direct comparisons for color, but I think that the excess Oxalic acid will be beneficial for several purposes. It will help eliminate any carbonate in the paper that might reduce the tonality of the final print. It will also help make the print clear easier after development.

I'm sure there is a point where the benefits are compromised by some other drawback, but making a subtle change in the formula in this manner may make your life easier.

I typically use more EDTA in the FO mix than is called for in the books for a similar reason.


---Michael

I also use more EDTA and Oxalic Acid than some formula call for, but then there's a range of formula out there, too. I've found that if I have too much EDTA or Oxalic Acid in the FeOx it just precipitates out and doesn't cause problems with the printing.

 

[Jimmy Peguet]

Jorge, William, Michael and other, which FO formulas do you use ?

Mine is 0.5 g acid oxalic and 6.6 g FO for 25 ml water (FO bought from BS or Artcraft).

 

[nze]

Hi Jorge

In the Pizzigheli and Hubl Book about Platinotype.They speack abput the effect of pH of the developper. And they conclude that acid developer make cooler print than alkalin one. years ago I make some test with some ferric salt with different pH and conclude that this may also be applied to sensitizer.
to get warmer print, instead of usind hot developper the use of Basic bath result in really warm tone. the better are carbonate bath. For sure it is harder to take the ferri calt out after this developer but in traditional platinum palladium the more acid the less warm.

 

[Jimmy Peguet]

Hi Christian,

The formula I use is the one I taught from you, and I've always used it without any questions. So what is the role of oxalic acid in the sensitizer ? I thought it was used mainly to help dissolving FO, I had never thought before reading you all it could have a real impact on color print.

 

[Jorge]

Thanks Christian.

Jimmy I use a similar formula. I use .5 gr OA, 5 gr FO 27 ml of water. But I have used this without OA and it worked fine. IN this case I made a mistake and added 1 gr OA to the same formula. I get the feeling the OA was or is used to aid in acidifying the paper as we coat it. It seems we now have another variable to produce cool looking prints.

Ina nay case I dont like it, I will be more careful in the future..

 

[Jeremy]

So this is just taking the normal FO that I buy from B&S and adding oxalic acid?

 

[Kerik]

I use .5 gr OA, 5 gr FO 27 ml of water.

Hmmm... this is a pretty low FO concentration ~19%. I use ~27% solution - 6.75 gm FO, 1.2 gm OA and 0.5 gm EDTA (tetra) to make 25 ml. But, whatever works!

Kerik

 

[Jorge]

Hmmm... this is a pretty low FO concentration ~19%. I use ~27% solution - 6.75 gm FO, 1.2 gm OA and 0.5 gm EDTA (tetra) to make 25 ml. But, whatever works!

Kerik

Uh, you are right, I just went and checked. It is 7.5 gr of FO...

 

[Jimmy Peguet]

Kerik,

This is what I was wondering about Michael's answer above : what is EDTA used for in sensitizer ?

 

[Michael Mutmansky]

Jimmy,

I generally use:

FO 15g
OA 2g
EDTA 0.75g
H2O 55ml

If I have any trouble getting the FO into solution, I'll add a pinch or so more EDTA to the mix.

Note that the formula for FO is somewhat up to intrepretation, and you will find that the FO from one supplier will produce different results than the FO from another supplier. I believe theis is about the only compound that we use that is like this, with all the rest being more or less the chemical compound with a certain purity, and subject to little deviation.


---Michael