Yellow staining on cyanotypes

I recently went and made some cyanotype sensitiser using the classic recipe on alternativephotography.com, here: http://www.alternativephotography.com/cyanotype-classic-process/

When it came to printing, we were using fresh leaves, flowers etc. picked from the local area, and the paper we used was just cheap stuff from WHSmith (as a cheap first test, who cares?)

I was chuffed, first attempt and we got some great prints, however in others we found yellow staining to be slight issue. Persistent washing seemed to have a subtle effect, although it was so extremely slow that any difference it made, if at all, easily could've just been wishful thinking.

For one of the prints, I had held my hand over the paper for the entire exposure, and the areas where my hand was in contact with the paper exhibited this yellow staining (see attached). Also, some of the plants clearly held, and lost during exposure, a lot of moisture. We've therefore hypothesised, as no experts, that moisture is the cause of our yellow stains. A solution to this could perhaps be to dry our plants, but I'm not sure how that would affect the detail in them.

After having a bit of a google about, apparently a citric acid bath can help in removing yellow stains, but I imagine there's a plethora of reasons why you can end up with yellow stains and this might solve only one of them. Some places seem to state the paper can be the issue (although I imagine it's just that some papers are more susceptible to yellow staining than others?).

As ever I've come to photorio in the hopes that some photochemist boffins will have the answers to all my questions and more.

My questions are:

• Are we correct in assuming that the moisture caused our yellow stains?
• Will a citric acid bath help remove this type of yellow staining?
• Am I correct in assuming that certain types of paper are just more susceptible to yellow stains than others?
  
• Do we just need to be more patient when washing our prints?
• Should we perhaps dry our plants before using them to contact print?

Rainbow said:

• Are we correct in assuming that the moisture caused our yellow stains?

• Will a citric acid bath help remove this type of yellow staining?

• Am I correct in assuming that certain types of paper are just more susceptible to yellow stains than others?

• Do we just need to be more patient when washing our prints?

• Should we perhaps dry our plants before using them to contact print?

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* No
* Sometimes
* Yes
* No
* No

Try a different paper and adding a pinch of citric acid to your wash water. Cyanotype on a suitable paper does not require a lengthy wash and should yield a very deep blue/dmax after drying. Persistent yellow staining and lack of density in finished prints point towards unsuitable papers.

koraks said:

* No

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Are you sure? In the hand image provided, the stains are clearly localised to where my hand was in contact with the paper, and if you look closely there's a piece of acetate masking taped to the paper - my index and ring fingers' tips are atop this, and consequently, unlike my other fingers, didn't create yellow marks.

Rainbow said:

Are you sure? In the hand image provided, the stains are clearly localised to where my hand was in contact with the paper, and if you look closely there's a piece of acetate masking taped to the paper - my index and ring fingers' tips are atop this, and consequently, unlike my other fingers, didn't create yellow marks.

Click to expand...

So there may be something to the fact that the stains are localized at the point of contact and not global. But your first question was whether moisture from the hand caused this. There would not be any thing in the chemistry that I can surmise that would be affected by moisture on its own. So I concur with Koraks' answer. But there may be something else on the hand that might be changing physically or chemically on the paper/sensitizer which results in a yellow residue. Oils? Something alkaline? One way to check this definitively would be to use a plastic foil (like Saran wrap or equivalent) in between the paper and the hand. If the stains are absent that way, you have a hand in this...

nmp said:

there may be something else on the hand that might be changing physically or chemically on the paper/sensitizer which results in a yellow residue. Oils? Something alkaline?

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We had the same effect with various bits of foliage, I guess I must have something in common with my leafy friends besides respiration.