cyanotype question

[claras]

After reading a few APUG posts on the subject of cyanotypes, I set a couple of sheets of paper into a tray of water with a bit of diluted vinegar. After drying, coating and making the exposure I used a first clearing bath with a small amount of citric acid added. Now I immediately noticed a huge amount of blue being washed off!...something I never saw before using the vinegar and citric acid. And yet the resulting prints were, in my opinion, much better!
It's my understanding that both the vinegar treated paper and the citric in the first bath are for the purpose of retaining mid tones...and it seems to have done that.
Today, I made a print with only the vinegar treated paper and without the citric bath. Also a very improved result...but without any blue being dramatically washed away.
So now I'm wondering if it is the citric bath that caused so much blue going down the drain, or is it the combination of vinegar treated paper and a citric bath?
Anyone have any thoughts about vinegar treated paper vs citric acid bath?

 

[cliveh]

Have you tried it without using any acid?

 

[claras]

Have printed using the same negatives in the past without either vinegar paper or citric acid. Results were alright, but with more loss of mid tone. I am pretty well convinced that vinegar paper improves my images...and, I think, may reduce exposure time. It is really the combination of the treated paper and the acid bath I am wondering about. Is there any advantage to one over the other...and does using both result in more mid tone...and does it cause chemical being washed off?

 

[jp498]

The vinegar probably remove PH buffering from the paper, and the buffering can create all sorts of problems. Paper choice is a big deal.

The vinegar soaked paper could also be making the paper damp, which means it will soak in the cyanotype chemistry quicker/deeper than fresh dry paper. Some instructions say to brush on a little water prior to coating for this reason.

 

[tony lockerbie]

What JP says, the paper can have a very heavy buffering which the vinegar will remove/neutralize. Experimenting with different papers is very worthwhile.

 

[claras]

Thanks everyone. The paper I'm using is Crane's Weston Diploma Parchment.

 

[gandolfi]

I have used Zerkall papers for 25 years now - for all sorts of techniques - never needed any treatment of the paper prior to any process...

 

[jp498]

I've used Stonehenge and Arches Platine for cyanotypes and haven't needed any vinegar treatment.

 

[falotico]

acetic and citric acid washes for cyanotype

Commercial papers commonly are sized (coated) with gelatin or starch, both of which have an attraction for ferricyanide compounds. Adding these mild organic acids could increase this attraction by making the naturally acidic gelatin or starch even more acidic and thus even more likely to bind with the iron ferricyanide complex, (this also applies to ferrocyanide compounds). That would explain why the resulting print image is as strong or stronger than before.

I concur with the idea that these acids would overcome the buffers added to the paper and allow the reaction forming the cyan complex to proceed more aggressively. Lowering the ph in this way would not help the light sensitive reaction, which is Fe3+ =hv=> Fe2+, but it might make the ferricyanide more reactive, again making the reaction more aggressive.

In any case if the reaction proceeds more aggressively for whatever reason then more of the blue cyan complex will form--some even in liquid lying unbonded with the paper. More forms and there is more for the image and more to wash away in the clearing rinse.

 

[claras]

falotico@ Thank you. It hadn't occurred to me that chemical floating around in the water might also react.

 

[Mainecoonmaniac]

I've tried clearing cyanotypes with citric acid and it kills the Prussian blue. The blue goes towards green. I clear it in just plain water then soak in it hydrogen peroxide to intensify the blue.

 

[claras]

gandolfi@ jp498@ I will buy some of the paper you have mentioned. I don't know that Crane's Parchment really needs any treatment. It was mainly just to see if it would make any improvement. I'm afraid I'm one of those people who know how to drive a car...but I don't really know why it works.