Non-toxic oil prints again: residual iron test?

[NedL]

I've been stuck at home for the past 7 weeks with a disk problem in my neck... I'm finally well enough to drive and today will go pick up some Strathmore 400 printmaking paper to resume experiments with non-toxic oil prints. Among lots of different papers I've tried, this one worked the best ( for clearing, lack of gelatin blisters, and adhesion ).

Brief description of the process:

I had a blog about this before the new APUG site, but the basic idea is to make a relief image in gelatin, and ink it like a bromoil print. A mixture of Ammonium Ferric Citrate [AFC] and gelatin is coated onto paper and allowed to dry. Then the paper is exposed to UV or sunlight under a negative, and put into a weak solution of hydrogen peroxide. The hydrogen peroxide hardens the gelatin where it was exposed to light. The paper is then washed to remove the iron salts.

Later, when the gelatin is swelled for inking, the hardened areas accept ink and the softer areas contain more water that repels the oily pigments.

I've done a lot of experimenting with different papers, different amounts of AFC and ways of coating the paper, and learning the quirks of soaking and inking ( one trick is to use cool water only for this process ).

There is only (there was a url link here which no longer exists)... maybe not the best print, but it gives you an idea of what the results of this kind of printing is like.

Here's the question:

When I left off these experiments, everything was working pretty well, but I was not completely sure that all the iron salts were getting washed out. I spent a lot of time trying different combinations of citric acid, EDTA, sodium sulfite, and other things to make the gelatin perfectly clear. This created various other problems with blisters and with the gelatin coming off the paper and in some cases ( oxalic acid ) affected the gelatin relief image itself.

I got to the point where the gelatin was almost clear, and clear enough that the resulting prints look good, but there are doubts remaining! You have to look closely to see that the dried gelatin is not water-clear.

What I learned from PE and others here:

1) wet gelatin is slightly yellow, and becomes clear when it is dry.
2) I think it was APUG member Hexavalent who pointed out that iron-hardening gelatin causes a slight yellow color.

When there is a very slight amount of yellow tint left, I don't know if it is residual iron or if it is a natural consequence of hardening gelatin with AFC. I'd like to be able to test for residual iron to be certain. Searching the web for residual iron tests only came up with a couple of very complicated possibilities.

Any thoughts/ideas/suggestions??

Some other thoughts:

All this, and especially my experience with EDTA, has made me skeptical about Halvor Bjoerngaard's "Chiba system", and whether the iron salts are really completely removed in his process... his hardened gelatin has pigment mixed in, so it would not be possible to see any remaining yellow color. His assumption is that a soak in di-sodium EDTA removes the iron, but this was not tested. My experience so far leads me to think it is far from certain and there are a lot of variables in play ( paper, acidity, %AFC in gelatin, how long in the hydrogen peroxide, etc etc! )

How I'm going to start up again:

I've noticed the yellow washes out most quickly during the soak in hydrogen peroxide ( which itself is slightly acidic, so should not promote formation of insoluble iron salts ). I'm planning to increase the time in the hydrogen peroxide bath, change it several times, followed by plain water wash or with just a pinch of citric acid. Reading over my notes, this seems like the most promising approach. Some kind of residual iron test would sure help.

 

[pschwart]

some suggestions:
- Some gelatins are whiter than others. Start with one of these
- A thinner gelatin coating will minimize visible yellowing
- Be sure your papers are sufficiently sized and hardened before coating with the sensitized gelatin
- You may not want to go this route, but FYI: a dichromate sensitizer is easily cleared using potassium metabisulfite
- Use the inked print as a matrix and run it through an etching press (Rawlins oil transfer). Another benefit is you can make multiple
prints from the same matrix

I've been stuck at home for the past 7 weeks with a disk problem in my neck... I'm finally well enough to drive and today will go pick up some Strathmore 400 printmaking paper to resume experiments with non-toxic oil prints. Among lots of different papers I've tried, this one worked the best ( for clearing, lack of gelatin blisters, and adhesion ).

Brief description of the process:

I had a blog about this before the new APUG site, but the basic idea is to make a relief image in gelatin, and ink it like a bromoil print. A mixture of Ammonium Ferric Citrate [AFC] and gelatin is coated onto paper and allowed to dry. Then the paper is exposed to UV or sunlight under a negative, and put into a weak solution of hydrogen peroxide. The hydrogen peroxide hardens the gelatin where it was exposed to light. The paper is then washed to remove the iron salts.

Later, when the gelatin is swelled for inking, the hardened areas accept ink and the softer areas contain more water that repels the oily pigments.

I've done a lot of experimenting with different papers, different amounts of AFC and ways of coating the paper, and learning the quirks of soaking and inking ( one trick is to use cool water only for this process ).

There is only (there was a url link here which no longer exists)... maybe not the best print, but it gives you an idea of what the results of this kind of printing is like.

Here's the question:

When I left off these experiments, everything was working pretty well, but I was not completely sure that all the iron salts were getting washed out. I spent a lot of time trying different combinations of citric acid, EDTA, sodium sulfite, and other things to make the gelatin perfectly clear. This created various other problems with blisters and with the gelatin coming off the paper and in some cases ( oxalic acid ) affected the gelatin relief image itself.

I got to the point where the gelatin was almost clear, and clear enough that the resulting prints look good, but there are doubts remaining! You have to look closely to see that the dried gelatin is not water-clear.

What I learned from PE and others here:

1) wet gelatin is slightly yellow, and becomes clear when it is dry.
2) I think it was APUG member Hexavalent who pointed out that iron-hardening gelatin causes a slight yellow color.

When there is a very slight amount of yellow tint left, I don't know if it is residual iron or if it is a natural consequence of hardening gelatin with AFC. I'd like to be able to test for residual iron to be certain. Searching the web for residual iron tests only came up with a couple of very complicated possibilities.

Any thoughts/ideas/suggestions??

Some other thoughts:

All this, and especially my experience with EDTA, has made me skeptical about Halvor Bjoerngaard's "Chiba system", and whether the iron salts are really completely removed in his process... his hardened gelatin has pigment mixed in, so it would not be possible to see any remaining yellow color. His assumption is that a soak in di-sodium EDTA removes the iron, but this was not tested. My experience so far leads me to think it is far from certain and there are a lot of variables in play ( paper, acidity, %AFC in gelatin, how long in the hydrogen peroxide, etc etc! )

How I'm going to start up again:

I've noticed the yellow washes out most quickly during the soak in hydrogen peroxide ( which itself is slightly acidic, so should not promote formation of insoluble iron salts ). I'm planning to increase the time in the hydrogen peroxide bath, change it several times, followed by plain water wash or with just a pinch of citric acid. Reading over my notes, this seems like the most promising approach. Some kind of residual iron test would sure help.

 

[NedL]

pschwart: All excellent thoughts, thank you!

I've got some "super clear" gelatin... it has it's own challenges ( harder to make a strong relief image with it ) and is how I discovered there is still slight yellow remaining ( compared to plain gelatin coated on the same paper ) I don't know if the remaining yellow is iron or if it is natural from the hardening.

I know for certain that I've been using thicker gelatin than is necessary. That's a great point.

Agree that sizing needs much more attention. PVA was a disaster, the gelatin slides right off! I've tried coating plain gelatin first but didn't see much improvement. But this needs more work.

Dichromates... avoiding them is the point of using AFC. ( Not from fear, but managing the waste... )

That's an awesome point that in the transfer process, who cares if there is iron in the gelatin! I've been trying to resist that particular rabbit hole... it wouldn't take much to push me in

 

[pschwart]

Agree that sizing needs much more attention. PVA was a disaster, the gelatin slides right off! I've tried coating plain gelatin first but didn't see much improvement. But this needs more work.

Some artist acrylic polymers work well (Golden GAC 100 is one example). Care required or you can ruin the special qualities of your watercolor paper.
Gelatin makes an excellent sizing, but the hardeners that work well (dichromate, formalin, glutaraldehyde) are toxic. I use formalin -- it's noxious but only a couple of drops are required, there is zero waste, and it's very reliable.

 

[NedL]

I'll get some GAC 100 or similar next time I'm at the art store, thanks! Too bad I didn't see your post in time, I just got home with my new paper. I take your point about sizing ( undiluted PVA really changes the look of the surface too, dilutions much nicer ) and of course the gelatin does too. If I ever get this process under good control, the next thing will be to try adding starches to minimize this. Thinner coats of gelatin should help a lot too.. I'm going to start testing with some really thin coatings, inking the result, and build it up only as much as necessary.

I'd prefer to keep the whole process pretty benign if I can, but the zero waste aspect of formalin is good and I'll try it if nothing else works.

Now to come up with a way to do a series of fairly quick tests ... on each one I will coat a strip of plain gelatin to the side, to provide a comparison, and I'll vary the sizing/coating/washing to see how close to clear I can get.

Cheers!

 

[pschwart]

- Lower concentrations of gelatin == lower gloss. I use 5% when sizing carbon supports, and that is a demanding application. You can probably get away with less
- You can also try fumed silica or even adding some matte acrylic to reduce gelatin gloss
- A single coat of albumen over a gelatin sizing works extremely well for carbon. Not sure if this is necessary for your oil prints, but fyi, albumen is easy to harden with a very quick application of isopropyl
- You might want to try some papers that don't require sizing (photo paper, Yupo, ...).

I'll get some GAC 100 or similar next time I'm at the art store, thanks! Too bad I didn't see your post in time, I just got home with my new paper. I take your point about sizing ( undiluted PVA really changes the look of the surface too, dilutions much nicer ) and of course the gelatin does too. If I ever get this process under good control, the next thing will be to try adding starches to minimize this. Thinner coats of gelatin should help a lot too.. I'm going to start testing with some really thin coatings, inking the result, and build it up only as much as necessary.

I'd prefer to keep the whole process pretty benign if I can, but the zero waste aspect of formalin is good and I'll try it if nothing else works.

Now to come up with a way to do a series of fairly quick tests ... on each one I will coat a strip of plain gelatin to the side, to provide a comparison, and I'll vary the sizing/coating/washing to see how close to clear I can get.

Cheers!

 

[NedL]

I used 3% gelatin for sizing when tried it, and my gelatin containing AFC has varied from 3% to 10%, depending on whether I applied multiple coats or only one thicker single layer. Many of my prints were made with 3 layers of 3% gelatin + 1.5% AFC, no sizing. I didn't realize before now, but you're right, the glossiness is more noticeable on the ones with a single layer of higher concentration gelatin. That's interesting -- and sort of odd since it's about the same total amount of gelatin.

With the paper I'm using now, the gelatin adheres well without any additional sizing ... so the real question is if washing works better with sizing, by keeping the AFC+gelatin from sinking into the paper at all. I've thought about albumen and IPA... and that would be an excellent thing to try before going to more extremes. We've got four ducks laying big eggs every day, so no shortage of albumen.

Off to coat some paper now....

 

[NedL]

Yikes I'm guilty
There are a lot of threads on photrio where someone is working on something, gets suggestions from the forum, and then we never hear what happened. Right now I am playing around with replacing dichromate with AFC for a totally different process, and a google search found this thread from a little over a year ago.

Here's what happened. I spent a couple more weeks after this post trying and failing to get a perfectly clear gelatin relief matrix, until some di-sodium EDTA I ordered arrived in the mail... and that was the real solution. Using a 1% solution of di-Na EDTA made the results perfectly clear, and I really need to retract the skepticism I wrote above about Halvor Bjørngård's clearing. I can't say there is NO iron left in the reliefs, but visibly, they now appear perfectly clear. The slight yellow I was seeing really was residual iron, and not the natural color of the gelatin.

So, if you are attempting a process that uses AFC to harden gelatin, make sure to get some di-sodium EDTA and don't waste lots of time trying tetra-sodium EDTA or other things...

 

[Andrew O'Neill]

Thanks for the update, Ned!