Classical cyanotype sensitizer solution leaves powdery blue-green residue

Vandita · Jun 8, 2021

Hi good people!

I am relatively new to the classical cyanotype process. I have mixed my chemicals before but am facing a new problem.

My Solutions A and B look alright on their own (25g FAC and 10g Pot Ferrocyanide each in 100cc distilled water). However when I mix them to make sensitizer a strange reaction seems to take place which makes the whole thing turn a bright deep green and leaves a fine powdery residue which is impossible to filter (image 1).

When I coat the paper with this solution the powder gets lathered on with the bright green solution and dries much greener (image 2) as compared to the usual chartreuse yellow I am used to getting.

The image I get from this has significantly blue highlights, although the shadows are a nice saturated blue (image 3). I previously had clear whites for the same exposure from this very negative.

For testing, I developed an uncoated paper in water, and it did not leave the paper clear like it should. Some light blue was left.

Could it be that the dry FAC I used was exposed to light and so its solution formed insoluble ferric ferricyanide powder when it came in contact with solution B?

Waiting to hear from the community.
Vandita
https://www.instagram.com/van.devi/

Andrew O'Neill · Jun 8, 2021

How fresh is stock A? After a few days it can go bad and moldy. In regards to lighting, I work under a yellow bug light.

Herzeleid · Jun 8, 2021

Your mixture's color shows that prussian blue pigment is formed upon mixing. Most likely, FAC solution contains ferrous ions. It might be a result of storage conditions of powder, it might be light exposure or it might be heat. I assume you keep your solutions in amber bottles and away from strong light sources.

To remedy this problem you can add hydrogen peroxide to you FAC solution and ferrous iron will be oxidized to ferric iron. In order to prevent diluting your solution use high concentration of peroxide. A few drops of 30 or 50 percent hydrogen peroxide added in to your FAC solution could fix it. After adding one or two drops of peroxide, throughly mix your solution then on a white plate/dish mix one drop of newly mixed FAC with a drop of PFC. If you see no color change, then the problem is fixed.

fgorga · Jun 8, 2021

Andrew O'Neill said:
How fresh is stock A? After a few days it can go bad and moldy. In regards to lighting, I work under a yellow bug light.

In my experience both traditional cyanotype stocks are very stable when stored away from light. I routinely use solutions that are months old.

Yes, will grow mold rather quickly in the ferric ammonium citrate but as long as you avoid getting the mold on your paper the solution works just fine. When I have a moldy solution, I simply filer the amount I need to use right before mixing the solutions together.

As far as lighting goes, if you stay away from fluorescent bulbs and day light and stick with dim(ish) light otherwise, you should be fine.

I work in my basement which has a number of overhead light fixtures. These have been converter to warm LED bulbs in the area where I do alt process work. I just leave them on these days for both cyanotype and salted-paper without problems.

fgorga · Jun 8, 2021

Herzeleid said:
Your mixture's color shows that prussian blue pigment is formed upon mixing. Most likely, FAC solution contains ferrous ions. It might be a result of storage conditions of powder, it might be light exposure or it might be heat. I assume you keep your solutions in amber bottles and away from strong light sources.

To remedy this problem you can add hydrogen peroxide to you FAC solution and ferrous iron will be oxidized to ferric iron. In order to prevent diluting your solution use high concentration of peroxide. A few drops of 30 or 50 percent hydrogen peroxide added in to your FAC solution could fix it. After adding one or two drops of peroxide, throughly mix your solution then on a white plate/dish mix one drop of newly mixed FAC with a drop of PFC. If you see no color change, then the problem is fixed.

I agree with this assessment of the problem.

Personally, I would just purchase a new batch of 'FAC' from a reputable vendor.

The addition of peroxide might well work. (I have no experience here.) However, be warned that concentrated peroxide solutions are very nasty. Be very careful and where good protective gear.

In my career as a chemist, I used 30% hydrogen peroxide routinely. The worst chemical burn I ever received was from an small drop of this solution that was sitting on the lab bench unnoticed... I touched the drop with my finger hours after having cleaned up from the experiment. The wound it caused was deep and took a long time to heal. This occurred over 40 years ago and I still remember it! Beware!!!

nmp · Jun 8, 2021

I wonder why not just use a dilute (like 3%) peroxide solution to make the FAC solution - instead of adding the concentrated version drop-wise.

:Niranjan.

glbeas · Jun 8, 2021

Another avenue for iron contamination is the water from the tap. I always use distilled to make these solutions to avoid tht problem

Herzeleid · Jun 8, 2021

nmp said:
I wonder why not just use a dilute (like 3%) peroxide solution to make the FAC solution - instead of adding the concentrated version drop-wise.

:Niranjan.

In the past, I had such problematic FAC and I had to source the chemicals from the same company for a few years. I have tested and I found that I needed to add at least 3, 4 to be safe, drops of 50% hydrogen peroxide for 25% FAC solution.

If I assume that a drop is 0,05ml then 4*0,05*50=X*3. 4 drops 50% H2O2 equals roughly 3,3ml of 3% H2O2.

However, while mixing FAC solution before adding all water to make the final volume of the solution, it is possible to determine the required amount with 3% peroxide. But if the solution is mixed in order not to dilute it further, concentrated peroxide helps.

nmp · Jun 8, 2021

Herzeleid said:
In the past, I had such problematic FAC and I had to source the chemicals from the same company for a few years. I have tested and I found that I needed to add at least 3, 4 to be safe, drops of 50% hydrogen peroxide for 25% FAC solution.

If I assume that a drop is 0,05ml then 4*0,05*50=X*3. 4 drops 50% H2O2 equals roughly 3,3ml of 3% H2O2.

However, while mixing FAC solution before adding all water to make the final volume of the solution, it is possible to determine the required amount with 3% peroxide. But if the solution is mixed in order not to dilute it further, concentrated peroxide helps.

I would then add 3% peroxide 1 cc at a time to this bad batch and test against K Ferri to see where it clears up. Then make a new batch with that much peroxide and water volume reduced by corresponding amount.

:Niranjan.

fgorga · Jun 8, 2021

nmp said:
I would then add 3% peroxide 1 cc at a time to this bad batch and test against K Ferri to see where it clears up. Then make a new batch with that much peroxide and water volume reduced by corresponding amount.

:Niranjan.

I concur... this is a much safer approach and 3% hydrogen peroxide is much more readily available than the more concentrated solutions.

If it turns out that you only need a few mL of 3% peroxide to 100 mL of the iron solution, I'd not bother to make anything new, you are not altering the concentration by much and I doubt the small dilution will matter. No evidence, just some chemical intuition.

Vandita · Jun 8, 2021

Thank you for arriving at this fairly easy fix Serdar, Niranjan and Frank. Its good you warned me about peroxide too. I will try this and report back.

Herzeleid · Jun 9, 2021

Vandita said:
Thank you for arriving at this fairly easy fix Serdar, Niranjan and Frank. Its good you warned me about peroxide too. I will try this and report back.

Your welcome. It would be easier to source %3 peroxide and safer to work with, if you follow niranjan's suggestion.

I just remembered and it is important. If you add H2O2 to your FAC mixture DON'T close the cap of your bottle for at least a day. FAC solution is acidic and H2O2 will decompose to water and oxygen.
You must let it gas out otherwise glass bottle might break or even explode from the increasing pressure.

Mike Ware · Jun 9, 2021

Potassium Ferrocyanide is the WRONG CHEMICAL for solution B. You should use Potassium Ferricyanide.
I'm surprised that no-one seems to have noticed this...

Herzeleid · Jun 9, 2021

Mike Ware said:
Potassium Ferrocyanide is the WRONG CHEMICAL for solution B. You should use Potassium Ferricyanide.
I'm surprised that no-one seems to have noticed this...

Uh oh. somethings only emojis can express.

Vandita · Jun 9, 2021

Mike Ware said:
Potassium Ferrocyanide is the WRONG CHEMICAL for solution B. You should use Potassium Ferricyanide.
I'm surprised that no-one seems to have noticed this...

This was my bad, a typo! I am using the potassium ferricyanide.

nmp · Jun 9, 2021

I saw that but ignored considering the OP showed the resulting image which would have been impossible with ferro.

Also the typo where "uncoated" instead of "unexposed."

Been there, done that.

:Niranjan.

Vandita · Jun 9, 2021

nmp said:
I saw that but ignored considering the OP showed the resulting image which would have been impossible with ferro.

Also the typo where "uncoated" instead of "unexposed."

Been there, done that.

:Niranjan.

One too many! Apologies.

I tested this out and it seems 0.1ml of 5-7% w/v peroxide in 10ml of FAC does the trick of not having any powdery residue. However, the colour of the sensitizer is still a little too blue-green and I maybe see some clouds of Prussian blue instead of the powder.

Coated with this anyway and exposed it. The blue was not as rich but the whites were clear! But I must test this once more because it was pouring today so the exposure might not have been sufficient for the blue to develop. 90 footcandles only for 4 hours. The test of developing "unexposed" paper in water was successful in clearing it of all blue.

I also unknowingly heeded Serdar's warning by not transferring the oxidized FAC into a bottle.

If all turns out ok with this solution, I am adding exactly the amount of H202 suggested by Serdar's formula assuming my solution is 5% (bottle says 5-7%). So then according to Niranjan's idea I should be dissolving 25g FAC in 98ml distilled water and 2 ml of 5% peroxide. Hope the elementary math is correct

Herzeleid · Jun 11, 2021

Vandita said:
If all turns out ok with this solution, I am adding exactly the amount of H202 suggested by Serdar's formula assuming my solution is 5% (bottle says 5-7%). So then according to Niranjan's idea I should be dissolving 25g FAC in 98ml distilled water and 2 ml of 5% peroxide. Hope the elementary math is correct

If the mixture is not clear of blueish color yet, you might consider increasing H2O2. Why not double it? You will have to add a lot of peroxide before FAC solution decomposes, so there is room for experiment.

Vandita · Jun 11, 2021

Herzeleid said:
If the mixture is not clear of blueish color yet, you might consider increasing H2O2. Why not double it? You will have to add a lot of peroxide before FAC solution decomposes, so there is room for experiment.

Yes true! I am not quite getting complete clarity in highlights yet and the shadows are very dull too because of the dilution, but that's not what I should be looking at at this point.

nmp · Jun 11, 2021

Vandita said:
Yes true! I am not quite getting complete clarity in highlights yet and the shadows are very dull too because of the dilution, but that's not what I should be looking at at this point.

This could get tricky.

If you have excess hydrogen peroxide over and above that is required for Fe(2) to Fe(3) conversion, it can presumably act as a restrainer so you might have to increase the exposure to get the same blue density in the shadows as you were getting before.

On the other hand, I got a contrary result from one experiment I did some time ago of adding some hydrogen peroxide to FAC / K Ferri sensitizer. I didn't have compromised FAC but I was thinking may be peroxide would act as a contrasting agent - giving me whiter whites like a dichromate would do. What I got was exactly the opposite, i.e. severe staining in the whites, even without any exposure. My theory at the time was that the buffer in the paper provided an alkaline environment which caused hydrogen peroxide to act as a reducing agent and not an oxidizing agent. ( Is this is feasible, anyone?)

So it can go either way...

:Niranjan.

Classical cyanotype sensitizer solution leaves powdery blue-green residue

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