Cyanotype color change w/ sodium bisulfite: what's going on?

[cpeterson]

Hi all, I'm looking for somebody who can explain to me the chemistry behind this reaction, and importantly, if the result be deemed "archival."

I put acrylic gloss medium over a VDB print a few months ago and got a better dmax and an interesting brush texture. Great. Last night I tried it on a cyanotype ("new" photo formulary kit) and had some really unusual results: the acrylic medium not only enhanced d-max, but it also boosted contrast significantly and shifted the tone toward deep purple!

From the acrylic medium MSDS ("Preservative - Non Hazardous At Level Used") I presumed that the active chemical was sodium bisulfite, and a different cyanotype treated in a 10% bath of sodium bisulfite exhibited a similar purple shift.

I'm about to start printing a series of large cyanotypes that I intend to show and possibly sell, and I find this effect desirable, but I'm wondering what's going on chemically here, where the purple cast represents a chemical shift in the pigment, or if it's the result of chemical damage. Or more directly, whether this process is archival.

Speculation welcomed.

Cheers,
Conor Peterson

FWIW: the attached image was 9 drops of sensitizer + 2 drops citric acid 40% on Arches Hot Press 140lb, bathed post-exposure in a bath of 1% citric acid before final wash.

 

[patrickjames]

I can't help you but it sure looks good.

Patrick

 

[Photo Engineer]

Ammonia can boost cyanotype density and change color. Acrylics contain amines, close relatives to ammonia.

Just a wild guess.

PE

 

[smieglitz]

I just googled acrylic gloss medium and found the same in regard to ammonia content. I also downloaded a MSDS for a popular acrylic gloss medium and varnish, and the pH was listed at between 8-9 making it an alkaline material.

The lavender color is probably from the reaction of the cyanotype with the high pH solution and unfortunately, it is also probably fugitive. In my experience, alkaline solutions also bleach cyanotypes so I would expect to see not only the color fade, but also the image density reduce.

You can observe the color change in cyanotypes and the bleaching effect by immersing a freshly printed cyanotype into a tray of water to which a few drops of ammonia (or film developer, borax or any other common household alkali, etc.,) has been added. It is a neat trick for saving overprinted cyanotypes and reducing their density. Washing the print in acidified water (add a few drops of stop bath to the tray) will restore the blue color but the print will have bleached somewhat.

I wish there was some way to fix the lavender color, but there is none that I know. I think the only toner that is marginally permanent with cyanotype is tannic acid (found in tea) which produces more neutral colors.

joe

 

[smieglitz]

Forgot to mention that the boost in density and contrast that you are seeing is probably a physical change in reflection rather than chemical change. I think you would see the same thing density-wise by employing any sort of varnishing agent, gelatin, gum arabic solution, albumen, starch sizing, PVA, etc.

 

[patrickjames]

Just an idea, but wouldn't sealing the print in the acrylic at least offset the fugitive nature of the change in ph? Anyone have any ideas on that?

Also, what would be the long term chemical and fading effects of the change in ph if it wasn't sealed? Would it revert back to a cyan tone?

Patrick

 

[cpeterson]

You can observe the color change in cyanotypes and the bleaching effect by immersing a freshly printed cyanotype into a tray of water to which a few drops of ammonia (or film developer, borax or any other common household alkali, etc.,) has been added. It is a neat trick for saving overprinted cyanotypes and reducing their density. Washing the print in acidified water (add a few drops of stop bath to the tray) will restore the blue color but the print will have bleached somewhat.

What an excellent reply, thank you! I suspected that the purple was fugitive. Having already been disappointed over the failure of the excellent warm tones I was seeing on my partially ferri-bleached silver-gel prints to survive a second fixing, I knew not to get too excited over this unexpected color shift.

I didn't want to complicate my original post, but to rule out the sulfur in sodium bisulfite, I tried another base, sodium hydroxide. I was expecting -- and observed -- a pretty strong reaction! A drop or two of NaOH at a medium strength took the cyanotype from dark blue to lavender to light purple to near-white within seconds.

I was using Art Advantage acrylic gloss varnish (http://www.art-advantage.com/msds/3240.pdf) which I doubt is archival in the first place. From what I understand, cyanotypes need paper with a neutral pH to be properly archived, basic or buffered environments are said to be hostile. Well, this acrylic medium fails on that point, so already the idea of sealing in the purple color with the coating is out.

At any rate, I plan to explore this further, so I'll keep APUG updated in this thread if anything emerges.

Further advice still welcomed, of course.

 

[Loris Medici]

You can use Hydrocote Polyshield Clear Gloss polyurethane wood finish for the same purpose.

This material also is slightly alkaline and can give your cyanotypes a slight lavender cast *when used undiluted* but the cast reverse in a couple of days without any perceptible density loss and/or bleaching of highlights.

(Speculating ON) To be on the safe side, you can clear (not develop!) your prints in a mild (2%) citric acid bath. By doing so, citric acid molecules will be trapped inside the prussian blue lattice (this is highly probable -> see Mike Ware's book on Cyanotypes) and presumably protect the image from bleaching. (Speculating OFF)

I prefer to use it 1:1 diluted. That way, it will still improve dmax but without adding any (highly un-natural) gloss to the image. Of course the improvement won't be as much as when using it undiluted but it's sufficient to have convincing blacks...

BTW, Hydrocote can be considered as being archival since it doesn't yellow with time + it's original purpose is to protect wood in outdoor conditions. (Garden furniture, boats ect...)

 

[Marco B]

By doing so, citric acid molecules will be trapped inside the prussian blue lattice (this is highly probable -> see Mike Ware's book on Cyanotypes) and presumably protect the image from bleaching. (Speculating OFF)

Please note I'm not in the alternative processes yet, so beware of my possible ignorance, but in terms of archivability, isn't prussian blue supposed to be a highly stable pigment???

Prussian blue was one of the first non-natural pigments used in oil painting, and is still available to date as a major blue pigment for artists (I've used it several times myself). The artist quality oil paints are supposed to be able to last for centuries... so why is prussian blue in a cyanotype not archival?

Or is the archivability of oil paint "prussian blue" based on it's enclosure in the linseed oil?

 

[Akki14]

It's only nonarchival in a basic/alkaline enviroment. I've had cyanotypes bleach out and look like acidwashed jeans if they've been left in hard tap water for an hour or two.

Makes matting an interesting challenge considering all mat board made these days is "acid free archival" and usually buffered with chalk too making it completely NOT archival for cyanotypes
http://en.wikipedia.org/wiki/Cyanotype

 

[DrPablo]

As attractive as that color is, I usually don't regard it as good news when a cyanotype turns that color. As explained above, it most likely signifies an alkaline environment, which will reduce longevity of the image. The acrylic coating probably won't matter, because the chemical reaction is going on inside the emulsion itself. If you want to use the acrylic but you're not insistent on the color, you might consider impregnating the paper with acid before drying (i.e. a dilute vinegar bath or something). That way it's buffered against the alkali in the acrylic.

 

[DrPablo]

Please note I'm not in the alternative processes yet, so beware of my possible ignorance, but in terms of archivability, isn't prussian blue supposed to be a highly stable pigment???

Variably. It is much more stable in acid than alkaline environments.

Also be aware that the iron blue toners are chemically identical to Prussian blue, i.e. they cause the image silver to be replaced with ferric ferrocyanide, and images toned in this way are known to degenerate faster than plain silver images.

 

[Photo Engineer]

Our atmosphere is acidic due to the carbon dioxide and sulfur dioxide present. This results in the fact that any object that sits around which is capable of absorbing things from the air (such as paper) will gradually become mildly acidic. Ammonia or amines will gradually be neutralized.

Paints or overcoats using the type of resin noted in the OP use this effect to assist in curing the polymer. They are mildly alkaline and are cured by the acid in the air.

PE

 

[Loris Medici]

Hi Marco,

What made you think that I'm saying Prussian Blue formed with Cyanotype is non-archival? My comment about protecting the image from bleaching was suggested as a protective measure for the case where you want to overcoat it with something alkaline... DrPablo too explained / suggested something similar later.

From the book "Cyanotype" by Mike Ware:

"...Chapter 6 recommends development in dilute acid, which will destroy any unwanted alkaline buffer that may be present in paper and ensure that the print is left in a condition favorable to the Prussian blue, possibly by the incorporation of acid cations into its lattice..." (page 131)

Therefore my (and DrPablo's) suggestion of treating (or developing) Cyanotypes in a mild acidic solution definitely have grounds.

Unfortunately Prussian blue is absolutely not stable in alkaline environment. Also, not all Prussian Blues are created equal -> see Mike Ware's book for detailed / scientific information...

Regards,
Loris.

Please note I'm not in the alternative processes yet, so beware of my possible ignorance, but in terms of archivability, isn't prussian blue supposed to be a highly stable pigment???

Prussian blue was one of the first non-natural pigments used in oil painting, and is still available to date as a major blue pigment for artists (I've used it several times myself). The artist quality oil paints are supposed to be able to last for centuries... so why is prussian blue in a cyanotype not archival?

Or is the archivability of oil paint "prussian blue" based on it's enclosure in the linseed oil?

 

[Jordan]

What am I missing here? The OP said that when he treated another cyanotype in a straight 10% bisulfite solution, he found a similar shift in hue. Bisulfite solutions are acidic and reducing. Could you possibly have uncleared iron in your print?

 

[DrPablo]

Bisulfite anions are the conjugate base of sulfuric acid (H2O3-), and like the conjugate bases of most strong acids its pKa is close to neutral. With a pKa of 6.97 the acidity or alkalinity of a 10% solution is likely affected by other unrelated solutes in the bath (or paper) than the bisulfite itself.

 

[Katharine Thayer]

Prussian blue pigment and ammonia

Please note I'm not in the alternative processes yet, so beware of my possible ignorance, but in terms of archivability, isn't prussian blue supposed to be a highly stable pigment???

Prussian blue was one of the first non-natural pigments used in oil painting, and is still available to date as a major blue pigment for artists (I've used it several times myself). The artist quality oil paints are supposed to be able to last for centuries... so why is prussian blue in a cyanotype not archival?

Or is the archivability of oil paint "prussian blue" based on it's enclosure in the linseed oil?

Hi Marco,
I can't speak to Prussian blue pigment used in an oil medium; my experience and knowledge of pigments is limited to pigments in a gum arabic medium (watercolor paints and dichromated gum photosensitive coatings).

Prussian blue has become one of my favorite pigments for gum printing; I use it a lot. As far as stability: the lightfastness of Prussian blue watercolor paint is variable and depends on the brand more than most other pigments; I use a brand (M. Graham) which has been shown in tests, both the manufacturer's tests and independent tests, to be very lightfast. As to susceptibility to fading in an alkaline environment: Bruce MacEvoy mentions on handprint.com that Prussian blue (PB 27) can fade on contact with alkalis such as calcium carbonate, ammonia, or bleach, "but in my experience the alkali must be fairly concentrated to affect the color in a good quality pigment."

I've never seen any fading or color-shifting with Prussian blue, and tonight I did a quick test: I applied household strength ammonia to (1) straight Prussian blue watercolor paint brushed on paper and dried, and (2) the border of an old gum print made with Prussian blue pigment. I applied the ammonia to half of each swatch so that the two halves could be compared side by side for any change in color. The results are below. I let the ammonia sit on the color for several minutes in both cases and watched closely; I could see no change in hue on the ammonia side, nor could I see any fading. I attach scans of the two samples below. I drew a white line on each sample to show approximately how the samples were divided; in each case the ammonia was applied on the right side of the line.
Katharine

 

[Loris Medici]

Katharine,

This shows us nothing related to our subject (Cyanotypes). You should repeat this with a Cyanotype (or with pure Prussian Blue pigment). Your test may show us either that

a) Your ammonia is off (Somehow! I think this is unlikely - unless you have anosmia and can't tell if it smells or not...)

b) There are compounds [in binder / plasticiser / additive ect. in water color paint and/or hardened gum] which are protecting the pigment from alkaline hydrolysis.

All: see http://www.mikeware.co.uk/downloads/Conserving_Cyanotypes.doc for an article about Conserving Cyanotypes (and the methods / causes of deterioration and how to protect them)...

Regards,
Loris

...I've never seen any fading or color-shifting with Prussian blue, and tonight I did a quick test: I applied household strength ammonia to (1) straight Prussian blue watercolor paint brushed on paper and dried, and (2) the border of an old gum print made with Prussian blue pigment. I applied the ammonia to half of each swatch so that the two halves could be compared side by side for any change in color. The results are below. I let the ammonia sit on the color for several minutes in both cases and watched closely; I could see no change in hue on the ammonia side, nor could I see any fading. I attach scans of the two samples below. I drew a white line on each sample to show approximately how the samples were divided; in each case the ammonia was applied on the right side of the line.

 

[Marco B]

Katharine,

This shows us nothing related to our subject (Cyanotypes). You should repeat this with a Cyanotype (or with pure Prussian Blue pigment). Your test may show us either that

a) Your ammonia is off (Somehow! I think this is unlikely - unless you have anosmia and can't tell if it smells or not...)

b) There are compounds [in binder / plasticiser / additive ect. in water color paint and/or hardened gum] which are protecting the pigment from alkaline hydrolysis.

All: see http://www.mikeware.co.uk/downloads/Conserving_Cyanotypes.doc for an article about Conserving Cyanotypes (and the methods / causes of deterioration and how to protect them)...

Regards,
Loris

I agree, but here is also a bit of text about Prussian Blue as a pigment in oil paintings, taken from the National Gallery, London, website, which confirms its (un)stable nature in different environments and paints:

"Fading and Colour Change of Prussian Blue: Methods of Manufacture and the Influence of Extender
Jo Kirby and David Saunders

The tendency of Prussian blue to change colour or to fade was widely known from the mid-eighteenth century onwards. This study investigates the influence of the method of preparation on the properties and stability of various Prussian blues, as well as reversibility of the colour change in painted samples of the pigment. A comparison is made between characteristics observed in examples of Prussian blue in paintings in the National Gallery Collection and those found in laboratory-prepared and collected historical samples of the pigment."

Still makes me wonder how they achieve the highly stable nature in modern oil paints, because the artist quality paint that I have lying around ("Rembrand 508" which does use the official PB27 Prussian Blue pigment) is marked as highly stable (three pluss's), which should guarantee centuries of life time if properly used... :confused:

 

[Marco B]

And two other strange articles regarding Prussian Blue. It seems there is even a "darker site" to Prussian Blue and cyanotype, the first article will certainly make me look different to cyanotypes the next time

* "Expert Report About the Formation and Detectablility
of Cyanide Compounds in the ‘Gas Chambers’ of Auschwitz"

Chapter two is called "Formation and Stability of Prussian Blue"...

http://www.germarrudolf.com/persecute/docs/ListPos17_e.pdf

* From http://www.riotinto.com/documents/ReportsPublications/Issue_82_-_The_Colour_of_Metals.pdf:

"Blue grass and red faces
Prussian Blue, discovered accidentally in 1704,
is the oldest of the chemically synthesized
colours. It is made by complex reactions between
dissolved iron and potassium ferrocyanide, which
happens to be one of the few chemicals that
dissolves gold.
Some years ago an imaginative mining
company had the idea of using weak cyanide
solutions to dissolve gold from buried gravels in
an historically important Australian goldfield. The
gold was certainly there, in a permeable gravel
layer with impermeable rocks above and below.
The plan was to drill a pattern of boreholes
that would allow cyanide solution to be pumped
down some holes, percolate through the gravel
layer, and be pumped up through other holes
carrying dissolved gold. It was a variation of a
standard technique, and standard technology
would turn the dissolved gold back into metal.
The whole idea seemed very attractive. For
one thing, there would be no mining as such, and
very little occupation of the land. The approach
was similar to harvesting a crop, and once any
piece of land had been harvested it could quickly
be returned to its normal use as high quality
pasture.
The fly in the ointment was a mineral called
marcasite, an iron sulphide with the same
formula as pyrite but a much greater tendency to
decompose in moist air or slightly acidic
groundwater. The gravel layer was impregnated
with marcasite, and when cyanide solution was
pumped in through trial boreholes the reactions
that produce Prussian Blue started up.
Luckily they could be damped down and
stopped, as soon as it was realized what was
happening. Blue grass and red faces were
avoided, but it was a reminder that pioneers are
always at the mercy of the unexpected."

 

[Loris Medici]

An educated guess would be: the binder for oil painting (linseed oil - which is very rich in omega-3, 6 and 9 fatty "acids") is protecting the Prussian blue... (Maybe it neutralizes the alkali before it starts to harm the pigment?!)

Regards,
Loris.

...Still makes me wonder how they achieve the highly stable nature in modern oil paints, because the artist quality paint that I have lying around ("Rembrand 508" which does use the official PB27 Prussian Blue pigment) is marked as highly stable (three pluss's), which should guarantee centuries of life time if properly used... :confused:

 

[Katharine Thayer]

Katharine,

This shows us nothing related to our subject (Cyanotypes). You should repeat this with a Cyanotype (or with pure Prussian Blue pigment). Your test may show us either that

a) Your ammonia is off (Somehow! I think this is unlikely - unless you have anosmia and can't tell if it smells or not...)

b) There are compounds [in binder / plasticiser / additive ect. in water color paint and/or hardened gum] which are protecting the pigment from alkaline hydrolysis.

Loris, I know this isn't directly related to cyanotypes; that's why I used the title "Prussian blue pigment and ammonia," why I quoted Marco's question directly, and why I addressed Marco specifically, so as to make clear that I was responding to Marco's question, not to the OP. My test was not intended or assumed to support or disconfirm theory or observations about alkaline fading of cyanotypes.

Marco's question was about Prussian blue pigment as used in paints, and as I said to him, my answer was only about watercolor paints not about oil paints, but I was curious, and that was what I found.

The ammonia was fresh and quite odorous.

Whether using powdered pigment would be a better test of the action of an alkali on pure PB 27 is a good question, but that wouldn't have addressed Marco's question about the pigment as used in paint.
Regards, Katharine

 

[Katharine Thayer]

Still makes me wonder how they achieve the highly stable nature in modern oil paints, because the artist quality paint that I have lying around ("Rembrand 508" which does use the official PB27 Prussian Blue pigment) is marked as highly stable (three pluss's), which should guarantee centuries of life time if properly used... :confused:

Hi Marco again,
As I said before, I know the pigment only as it is used in watercolor paints, (and by the way, the pigment I used in my test was also PB 27; when Loris suggested that my test would be more relevant if I had used "pure Prussian blue" I think he meant that one should use the pure powdered pigment rather than a paint which will contain other material besides the pigment and medium, not that he thought I wasn't actually using PB 27, which of course I was).

As I said in that first post, in watercolor paint the stability of the pigment varies widely across brands, and it's possible that in oil paint it may be the same. Prussian blue in three watercolor brands is rated extremely stable and in a few brands is so fadeprone as to be considered fugitive. My understanding from my reading in the past is that the difference in stability of different brands may have more to do with additives and fillers than with the medium itself; lower quality paints sometimes use a calcium carbonate filler to extend the pigment, which might have a deleterious effect on the pigment.

While we're looking at interesting facts about Prussian blue pigment, I came across some information on the U.S. Food and Drug Administration website that said Prussian blue has been approved as a drug to counteract the effects of radiation poisoning. I didn't save the URL, but if anyone's interested they could no doubt find it by googling the FDA and Prussian blue.
Katharine

 

[rwyoung]

[QUOTE
While we're looking at interesting facts about Prussian blue pigment, I came across some information on the U.S. Food and Drug Administration website that said Prussian blue has been approved as a drug to counteract the effects of radiation poisoning. I didn't save the URL, but if anyone's interested they could no doubt find it by googling the FDA and Prussian blue.
Katharine[/QUOTE]

Legend has it that some of the countryside in the path of the radiation cloud from Chernoybl was treated with Prussian Blue to lock up the radioactive elements... Don't know if that is true (in part or in whole) but it must have looked funky!

 

[DrPablo]

And two other strange articles regarding Prussian Blue. It seems there is even a "darker site" to Prussian Blue and cyanotype, the first article will certainly make me look different to cyanotypes the next time

* "Expert Report About the Formation and Detectablility
of Cyanide Compounds in the ‘Gas Chambers’ of Auschwitz"

Chapter two is called "Formation and Stability of Prussian Blue"...

Marco, this is a bit off topic, but you've quoted a report from Germar Rudolf, who is probably the most infamous of all Holocaust deniers, who was trying to disprove the presence of cyanide salt residue in the gas chambers. So, I'd hardly put any credence into his "science", which is appropriated highly selectively for him to prove an agenda.



Back to topic... Everyone here who argues about the instability of iron blue toners seems to neglect that they impart the same Prussian blue salt as in cyanotypes. I'd think, actually, that the blue-toned prints might be more stable than cyanotypes, because at least during stop bath and fixing you're impregnating the image with an acid. That's not necessarily something you do with any cyanotype.