What causes this in Traditional cyanotype?

[Akki14]

I mixed up a bit too much sensitised solution so I was running around my abode trying to find random paper etc to use the stuff on as I'm experimenting anyway.
I remembered one website said you could use it on natural fibre fabrics so I found some scrap cotton canvas and I was dripping the sensitiser solution on it and i noticed the drops formed yellow-green (which appears to be the normal colour judging by the two-dozen different papers I did previous to the fabric) but the edges of the drops went slightly more blue-green. I finished making it fairly even and the whole fabric went from a large splodge of yellow-green to a bluer green.

So what could cause the sensitising solution to go blue without exposure to UV? I was sensitising under a 15watt tungsten bulb which was about 2 metres away from the papers/fabrics so that shouldn't have caused it, I think. I might try printing with it anyway if it's dry by tomorrow even though I suspect it's completely wrong

 

[Akki14]

Oh dear the fabric has now gone totally dark blue Oh well, nothing to lose trying to print it tomorrow I guess... Will update either way.

 

[Davec101]

Sounds like the canvas is fogging. You need to find a more neutral PH material to work on, either that or treat the canvas before sensitizing with a bath of 5% hydrochloric acid.

 

[Akki14]

yeah I just tried printing it, albeit I didn't leave it out for as long as I should have and it has developed a print on it but without any good highlights. Next time I'll plan a bit better and give it another try. Might be nice to try and acidify the canvas, stretch it, sensitise it and print it one day.

 

[Akki14]

Stranger and stranger...after it dried, the highlights have gone a funny colour. The back of the fabric where the sensistiser was has gone the same funny colour.
http://www.stargazy.org/photos/cyanotypes/tn/cyanotypefabric.med.jpg

 

[Troy]

I've heard that it really depends on what kind of fabric you're talking about. Anything but clean, high-grade silk or cotton will have all sorts of funny processing chemicals and impurities in it. That's what I heard anyway.

 

[chrisofwlp]

That yellow tint in the highlights is staining caused by unexposed sensitizer. Perhaps you wash time was not long enough.

 

[Akki14]

but that yellow stain didn't appear until after washing. It sort of "developed" to that yellow. Is that still sensitiser?

 

[Loris Medici]

Do not print Cyanotype on painting canvas!

Akki, that particular canvas is probably coated with something that chemically interacts with Cyanotype sensitizer. If it's a piece of canvas for oil painting then the coating is highly alkaline gesso (traditional: rabbit skin glue + titanium dioxide + calcium carbonate, modern: acrylic medium + titanium dioxide + calcium carbonate) and there's no way to make decent cyanotypes on that material - calcium carbonate is cyanotype killer! You should use perfectly pure and unsized cotton and/or silk for cyanotype. Some pure cotton fabrics come with sizing -> you can get rid of the sizing by boiling and rinsing the fabric a couple of times (fresh water each time). Watch for your water too; if it's alkaline, you may add a pinch of citric acid in your wash water to acidify it.

Hope this helps,
Loris.

 

[Akki14]

This is more or less pure cotton canvas as in the material not the artist's medium. We bought it on a huge roll for re-covering theatre flats (large background type canvas & wood things) and I got the offcuts for free. It's not been sized or gessoed or anything of the sort. Just hadn't been washed as I was in a bit of a rush in the circumstances.

 

[Loris Medici]

This is more or less pure cotton canvas as in the material not the artist's medium. We bought it on a huge roll for re-covering theatre flats (large background type canvas & wood things) and I got the offcuts for free. It's not been sized or gessoed or anything of the sort. Just hadn't been washed as I was in a bit of a rush in the circumstances.

I see. But the fact that you're experiencing fogging right after coating implies that there's something wrong with the material - Cyanotype, especially New Cyanotype is a very good purity tester; you'll get inferior results with non-pure / non-suitable materials. Pure cotton never fogs - at least in my experience (I tried at least 4 different cotton fabrics from different sources and never experienced fogging). Does the same sensitizer work well with other substrates? Are you using the same tool for coating and/or the same coating method? Are you using the same water? BTW, don't overlook my suggestion of using silk -> it's a beautiful and most noble fabric for your fine-art prints + it needs neutral/acidic environment - just like Cyanotype.

Another note: I don't include dichromate in my classic sensitizer; I use dichromate just in the new formula. Maybe dichromate tans and stains the fabric?

Hope this helps,
Loris.