Oxalic acid pre soak or Potas Oxalate additive?

[dpurdy]

I am finally getting smooth prints on my Cranes after soaking the paper for a short while in 2% Oxalic acid. It gets rid of the mottling and makes the blacks very black.

what I am wondering is if the same thing would be accomplished by adding Oxalic Acid to the Potassium Oxalate developer. I hate to put a bunch of Oxalic acid in my developer and ruin it. But is the Oxalic acid really helping with coating or is it helping more with the processing? My coatings look very smooth without it but the prints get very mottled in the developer it seems.

I guess the obvious thing is to try a small amount.

Dennis

 

[Vaughn]

I have heard of putting Oxalic acid in the Ferric oxalate solution, but not in the developer. This was something suggested by Terry King of Great Britain. I don't have the details. He suggested it on a forum rather than soaking the paper in Oxalic acid (forum is no longer available).

I just printed on some Cot320 that I soaked in a 3% Oxalic acid bath and got some of the nicest prints that I have made in a long while. Coating was a dream -- about three passes with the glass rod, and finished off with a brush.

Vaughn

 

[photomc]

Might consider this, if you are using Potassium Oxalate for a developer, it alreay has oxalic acid in it. When you treat the paper with it, you are removing the buffers in the paper. To my knowledge adding more to the developer will only lower the pH of the developer is all.

 

[dpurdy]

I have always put some Oxalic acid in my Pt A and B and I have heard you need to tune up your Potas Oxalate with a bit of Oxalic acid now and then to keep it acidic. However I tested it today by exposing a sheet and cutting it in threes and processing one in my old developer and one in my fresh clear developer and one in my old developer with quite a lot of Oxalic acid in it and they all processed out exactly the same with the exact same mottling. Back to the drawing board.
Dennis

 

[clay]

I am strictly speculating here, but I think the reason that the oxalic acid pre-soak works is that it neutralizes the basic buffers in the paper fibers. The problem with archival buffered papers is that the buffers react with the wet pt/pd chemistry when it is coated onto the paper. So by the time it gets to the exposure and the subsequent development, the damage has already been done.

I know that paper acidity is a huge factor. I have some no-longer-available Whatman's watercolor paper that tests about pH 5.5, and it gives the best one-coat pt/pd print I have ever seen. The only knock on it is that it is very textured, (a 'not' paper) and the texture just screws up anything but a print done on a full sheet. I have always wondered if I could get somebody to put this stack of paper through a gravure press and calendar it. It would be awesome stuff if it were smoother.

Of course, this could just be the turnips talking.

 

[scootermm]

test the PH of your developer (B&S sells a reasonably priced PH tester which youll find immensely useful) Assuring its still acidic. If your fresh clear developer, old developer, and old dev with more Ox Acid, are all the same PH then its not surprising you are getting exactly the same mottling. Your Pot Ox dev is a combination of Potassium Carbonate and Oxalic Acid.

As youve experienced, and as mike has pointed out... the reason you are getting better black etc with the presoak is because the acid prebath is nuetralizing the buffer agents that are used in MANY papers. Imagine you might actually be noticing bubbling occuring when you are presoaking the paper? thats the neutralization.
Just keep presoaking your paper in an acid bath and you'll be better off. I often times will by 3 (10 sheets) pkgs and cut them in half and presoak all 60 sheets in a large tray of acid prebath and will have paper for a good long while.

One thing to note. your Pt/Pd solution A... is Ferric Oxalate Fe2(C2O4)3.5H2O it contains Oxalic Acid. by adding more Oxalic acid to your Solution A you are increasing the oxalic acid concentration.

 

[Ian Leake]

The "standard" Ferric Oxalate Solution A has, according to Arentz, 1 gm of Oxalic Acid for every 15 gms of Ferric Oxalate. The Oxalic Acid changes the speed of the coated paper (i.e. exposure times), and I've a suspicion it may also change the contrast too (but I've not done enough testing to be sure about that). Straight Ferric Oxalate needs at least 15-25% longer exposure times, more with some negs.

 

[dpurdy]

Thanks to the suggestion of using the Oxalic bath I was able to make the smoothest prints I have made in about 15 years yesterday. My working procedure ended up being, 1 minute soak in 2% Oxalic acid, air dry completely, short humidification over my steamer, coat using NA2 as contrast agent, dry with hair dryer completely, short humidification then print under florescent tubes. I managed to make 5 8x10s in a row that are nearly perfectly smooth.

BUT here is the next problem. Every print but one were left with a couple of small spots that wouldn't clear. Round spots about 1.5mm in diameter. I left the prints in the HCA baths longer than usual and stood there adgitating for long periods of time and the small spots would't budge. Looking through the prints at a light bulb I can see the spots have a bit of brown color so I know they are not clear. I guess I will try reclearing though I don't see how that will help. I guess I could use a stronger than normal clearing bath but I hate to damage the predominantly palladium image. Any suggestions?

 

[Vaughn]

One possibility -- I get lots of bubbles forming on the surface of the paper when in the Oxalic acid bath (chemical reation between the alkaline sizing and the acid). I make sure that I get these off the paper, as one might get uneven soaking in the acid. I wonder if the print color might slightly change, as well as the exposure rate, in areas not fully acified.

Second point...be aware of blow-drying platinum/palladium prints. I now have low-grade asthma (possibly platinosis) due to breathing platinum and/or palladium dust from blow-drying the coated paper. (see 8.008 in OvereXposure by Shaw & Rossol). It took me five years for it to happen. Most people might go their whole lifetime without problems. It started off as a sore throat that lasted for 3 days after each printing session, then a deep cough which lasted a few days without any other sign of illness. Conditions improved when I began to wear a good quality dust mask. I no longer have problems after printing sessions, and even have nicer prints, by air-drying coated paper for 1 to 2 hours with a fan. But I do have a slight background level of asthma that I now just live with...not too bad really.

Again, most folks might never have any problems...just be aware of any symptoms that seem to correspond to one's printing sessions.

Vaughn

 

[rbergeman]

thanks, vaughn, for the tip about air-drying and potential for platinosis -- and sorry to hear about hour first-hand experience with it ...... it serves as a sobering reminder not to take lightly the toxity of our materials ..... guess i need to stock up on some masks!

rich

 

[Vaughn]

thanks, vaughn, for the tip about air-drying and potential for platinosis -- and sorry to hear about hour first-hand experience with it ...... it serves as a sobering reminder not to take lightly the toxity of our materials ..... guess i need to stock up on some masks!

rich

Hey, it allows me to understand what two of my triplets are going through -- they also have asthma...most likely due to being borm almost 3 months premature and their lungs did not get the chance to fully develop before needing to be used.

Vaughn

 

[Dana Sullivan]

Just to clear up some confusion; there are two separate things going one here with oxalic acid.

Soaking you paper: If you soak your paper in oxalic acid, you're neutralizing the akaline buffers that paper manufacturers add to make the paper 'acid free'. You're also physically treating the paper by swelling the cotton fibers, making them more likely to absorb your coating emulsion evenly and completely.

Adding Oxalic to Ferric Oxalate: Bostick & Sullivan has not been adding oxalic acid to our liquid ferric oxalate solutions since we moved to Santa Fe in 1995. Second off, our ferric oxalate will pass the silver nitrate test for the presence of oxalic acid, meaning it does not contain any residual oxalic acid from the manufacturing process. (My dad developed a process back in 1981 that removes any excess oxalic acid, ferric nitrate, nitric acid or water from the powdered ferric oxalate). This also means that our ferric oxalate will work well for Kallitype prints, since silver nitrate is the other main ingredient in that process.

It is correct though, that oxalic acid and ferric oxalate have a close relationship. Ferric Oxalate is a ill-defined molecule, which means it is actually a group of closely related chemicals that all act the same way. When you add oxalic acid to ferric oxalate solution, you're converting the ill-defined ferric oxalate into it's stoichiometric form. To make a long story short, the stoichiometric form is a 'balanced' solution that reacts more completely with the platinum and palladium, yielding richer blacks, smooth tonal separations and more contrast. (I have gone back and forth about adding it to our liquid grades, but for now I'm not going to change things.)

Does the residual oxalic acid in your pre-soaked paper have an effect on the ferric oxalate when you lay down your emulsion? Sure, there's probably enough left in the paper to change the ferric oxalate into it's stoichiometric form. If you add oxalic acid to your ferric oxalate, will it neutralize the buffers in the paper enough to make a difference? I doubt it. Our tests show that you can add about 15 grams of oxalic acid to 100 ml of 27% ferric oxalate before it begins crystalizing out. If you used 1 ml of ferric oxalate to make an 8x10 platinum print, you'd only be applying .15 grams of oxalic acid, hardly enough to neautralize the calcium carbonate buffer in the paper.

It's late, so I'm not making sense, but I hope this has helped clear up some misconceptions.