Cyanotype whites not clearing

nmp said:

In general, acid promotes formation of ferric ferrocyanide. So in my opinion, and experience with Classic cyanotype, adding acid, whether at the sensitizer level (I know Mike Ware has mentioned that adding some citirc acid in the sensitizer clears highlights in New cyanotype) or in the developer will increase density - at both ends, higher Dmax and greater propensity for highlight staining. Plain water developing will get cleaner highlights but at the cost of loss of Dmax.

:Niranjan.

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I mix 5ml of sensitizerr at a time in this way:
1. measure 5ml distilled or RO water.
2. add 0.50g Ferric Ammonium Citrate mix until dissolved.
3. add 0.25g Potassium Ferricyanide mix until dissolved.
4. add 0.25g Citric Acid mix until dissolved, takes a while.
5. Coat onto paper, covers 12x15 inch sheet of watercolor paper. Very green color.
6. Dry with fan and no heat until almost dry. Takes about 5 min.
7. Expose as with Classic, takes about half the exposure.
8. Develop with water. No need for more acid. The pigment is much less soluble.

This provides much more acid at the development sites than soaking in acid solutions and gives less acid in the developing solution, since it dilutes very quickly. Cyanotype development is almost instantaneous, so providing acid in situ is most effective and efficient. No bleeding occurs at this dilution. Works with even the cheapest watercolor papers.

The citric acid amount can be changed for some contrast control.

Happy Holildays.

Mike Ware on the role of Citric Acid in the fading of Cyanotype prints:

"..oxidisable organic anions do indeed promote photoreduction of the pigment. It may be significant that the anions effective in promoting fading in Prussian blue are also those that normally render iron(III) photoactive in its salts, and are consequently present in the cyanotype sensitizer. To improve the light fastness of cyanotypes, therefore, the presence of excesses of these free anions, such as citrate or oxalate, should be avoided. Since an acid development bath is desirable in the processing of new cyanotypes (Ware formula employing ferrioxalate sensitizer), it is better to use a very dilute mineral acid such as hydrochloric or nitric, rather than citric or oxalic acids, which have been previously recommended."

Page #260

Italics mine.

Very interesting, thanks for sharing @Raghu Kuvempunagar

Raghu Kuvempunagar said:

Mike Ware on the role of Citric Acid in the fading of Cyanotype prints:

"..oxidisable organic anions do indeed promote photoreduction of the pigment. It may be significant that the anions effective in promoting fading in Prussian blue are also those that normally render iron(III) photoactive in its salts, and are consequently present in the cyanotype sensitizer. To improve the light fastness of cyanotypes, therefore, the presence of excesses of these free anions, such as citrate or oxalate, should be avoided. Since an acid development bath is desirable in the processing of new cyanotypes (Ware formula employing ferrioxalate sensitizer), it is better to use a very dilute mineral acid such as hydrochloric or nitric, rather than citric or oxalic acids, which have been previously recommended."

Page #260

https://www.mikeware.co.uk/downloads/Cyanomicon_II.pdf

Italics mine.

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Raghu, that version of the Cyanomicon is the 2016-2017 version, not the latest 2020 version. I hesitate to provide a link since it's not my property, but these are all available on Mike Ware's website. The Simple Cyanotype was developed in 2019. My references are from the latest version.

From page 240:
7.4.11 Simple cyanotype: workflow summary
1. Unbuffered paper: choose side, mark up coating area
2. Syringe out sensitizer: add Tween to final strength ~0.25-0.5 %
3. Rod Coat:
~1.5 cc per 10 x 8 in. area: 5-8 ‘passes’ of coating rod
4. Dry in dark: 1-2 hours at room temp, or 40°C air for 10 minutes
5. Negative: density range from 1.8 to a maximum 2.8, in the UVA
6. Expose to UVA: until high values green and deep shadows reversed
7. Develop: ½ minute in ~1% citric acid; or water for more contrast
8. Wash: in non-alkaline, non-hard water for 10 minute.

Notice he recommends development in 1% citric acid. Your reference relates, I believe, to the New Cyanotype process where he studied the fade resistance due to process being new at that time. My method using 0.25g citric acid quickly dilutes in one liter of wash water to 0.025% which is very mild and should not cause any bleeding onto the margins or highlights.

gealto2 said:

Raghu, that version of the Cyanomicon is the 2016-2017 version, not the latest 2020 version. I hesitate to provide a link since it's not my property, but these are all available on Mike Ware's website. The Simple Cyanotype was developed in 2019. My references are from the latest version.

From page 240:
7.4.11 Simple cyanotype: workflow summary
1. Unbuffered paper: choose side, mark up coating area
2. Syringe out sensitizer: add Tween to final strength ~0.25-0.5 %
3. Rod Coat:
~1.5 cc per 10 x 8 in. area: 5-8 ‘passes’ of coating rod
4. Dry in dark: 1-2 hours at room temp, or 40°C air for 10 minutes
5. Negative: density range from 1.8 to a maximum 2.8, in the UVA
6. Expose to UVA: until high values green and deep shadows reversed
7. Develop: ½ minute in ~1% citric acid; or water for more contrast
8. Wash: in non-alkaline, non-hard water for 10 minute.

Notice he recommends development in 1% citric acid. Your reference relates, I believe, to the New Cyanotype process where he studied the fade resistance due to process being new at that time. My method using 0.25g citric acid quickly dilutes in one liter of wash water to 0.025% which is very mild and should not cause any bleeding onto the margins or highlights.

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I'm quite aware of Simple Cyanotype working process as I have used it many times. The comment Mike Ware has made on Citric Acid being an enabler of Cyanotype print fading is not meant for any specific Cyanotype process but is a caveat for those Cyanotype processes that introduce impurities that potentially destabilise Prussian Blue, Citrate and Oxalate ions being such impurities. He does use this to make a case in favour of using mineral acids for his New Cyanotype but the caveat holds for Simple Cyanotype as well and any process that uses an excess of Citrate in the sensitiser or uses Citric Acid in the developer.

gealto2 said:

Raghu, that version of the Cyanomicon is the 2016-2017 version, not the latest 2020 version. I hesitate to provide a link since it's not my property, but these are all available on Mike Ware's website.

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It's really OK to post a link; @Mike Ware has graciously published this on his website and referring to it IMO only makes it easier for people to find this useful information. The document is available on his downloads page: https://www.mikeware.co.uk/mikeware/downloads.html
The direct link to the Cyanomicon ed. 2020 is here: https://www.mikeware.co.uk/downloads/Cyanomicon.pdf

On the topic of Classic Cyanotype giving staining with a sulfamic acid wash, I am pretty sure that most of the stain is directly caused by the low pH and that this puts a limit on how acidic the wash can be. Of course this doesn't contradict the fact it will also increase retention of stain from other sources.
The likely explanation is that this liberates some ferric ions from the citrate complex, who together with the ferricyanide ions form an extremely strong oxidizer that then gets reduced by the paper. This intermediate compound is mentioned briefly in the Cyanomicons too (Table 3.1):

Ferric ferricyanide
Prussian yellow (or Berlin brown) Soluble; a powerful oxidant, easily oxidises water, and paper etc., being reduced via green intermediates (Berlin green) to Prussian blue

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Personally I use 1-10% vinegar depending on required contrast, applied with a spray bottle.

koraks said:

The direct link to the Cyanomicon ed. 2020 is here: https://www.mikeware.co.uk/downloads/Cyanomicon.pdf

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Thanks.

Page #288 of this version makes the same point on fading that I shared in my earlier post:

"To improve the light fastness of cyanotypes, therefore, the presence of excesses of these free anions, such as citrate or oxalate, should be avoided. Since an acid development bath is desirable in the processing of new cyanotypes (Ware formula employing ferrioxalate sensitizer), it is better to use a very dilute mineral acid such as hydrochloric or nitric, rather than citric or oxalic acids,"

AntonKL said:

Personally I use 1-10% vinegar depending on required contrast, applied with a spray bottle.

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Many use Vinegar and have no complaints but Mike Ware advises against its use:

"Acetic acid is not recommended because it tends to form insoluble strongly-coloured basic ferric acetate."

Page #229 of the same document.

Raghu Kuvempunagar said:

I'm quite aware of Simple Cyanotype working process as I have used it many times. The comment Mike Ware has made on Citric Acid being an enabler of Cyanotype print fading is not meant for any specific Cyanotype process but is a caveat for those Cyanotype processes that introduce impurities that potentially destabilise Prussian Blue, Citrate and Oxalate ions being such impurities. He does use this to make a case in favour of using mineral acids for his New Cyanotype but the caveat holds for Simple Cyanotype as well and any process that uses an excess of Citrate in the sensitiser or uses Citric Acid in the developer.

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Citrate ions are fundamental to classic and simple cyanotypes, they are not impurities. Oxalate ions are fundamental the same way in New Cyanotypes. Ware also mentions this. Simple uses more citrate, not less, although my stoichiometry skills are lacking in this case. If citrate was to be avoided, then everybody would be using brown ferric ammonium citrate, which has less citrate. I don't see a mad rush in that direction. Notably, the development of manufacturing green FAC was a universally agreed upon improvement. Honestly, it may well be the case that brown FAC results in more stable cyanotypes.

With the New Cyanotype process, Ware found greater fading than the other historical processes, so endeavored to mitigate that. That's pretty clearly the context. More importantly, nobody has ever claimed cyanotypes to be archival other than a few modern youtube channels. They fade away due to light exposure, and then they come back. Historical cyanotypes are not kept in brite sunlight to my knowledge. They are also the product of brown FAC generally, which may be more stable. Brown FAC produces sensitizers that are even higher in contrast than green, and about half as light sensitive. These practical matters have made it obsolete. Notably, by adding a little citric acid to a brown FAC sensitizer, it can be made to perform similarly to green FAC. Ware also discusses this in the Cyanomicon.

gealto2 said:

they are not impurities.

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I hope @Mike Ware will not mind me copypasting here a significant piece of text from his work.

Chapter 9 Vulnerability & Conservation of Cyanotypes
Section 3 Impurities destabilising Prussian blue
Page #288

"Fading of Prussian blue requires the simultaneous presence of several contributing factors: light; a reducing agent (electron donor) in intimate contact with the solid; and cations to migrate into the lattice and balance the increased negative charge brought about by reduction. Molecules that are small enough to be occluded within the voids of the Prussian blue lattice should be particularly effective in promoting the photoreduction. To test this possibility, pure Prussian blue coatings on paper were prepared by successive coats of potassium ferricyanide and ferrous sulphate, then part-coated with solutions of oxidisable anions such as citrate and oxalate, and allowed to dry. The density of the impregnated Prussian blue paper was compared with the control region after a period of dark storage to ensure that there was no reduction in the dark, then the whole sheet was given a standard fading exposure. The reductantcoated area was found to fade in the light much more rapidly than the control area, showing that these oxidisable organic anions do indeed promote photoreduction of the pigment. It may be significant that the anions effective in promoting fading in Prussian blue are also those that normally render iron(III) photoactive in its salts, and are consequently present in the cyanotype sensitizer. To improve the light fastness of cyanotypes, therefore, the presence of excesses of these free anions, such as citrate or oxalate, should be avoided."

Italics mine.

It is possible a thorough wash removes oxidisable anions completely from the print, but the text doesn't say anything about it.