Direct tannin process (no bleaching, no Potassium ferricyanide, just ferric oxalate/water and hydrogen peroxide + tannins)

[Raghu Kuvempunagar]

They may be but to what end is not clear to me.

:Niranjan.

In the case of Catechol toner, adding Peroxide to it makes it produce more dye/stain.

 

[nmp]

Oh yes, I think so. I was imagining mixing and using immediately. The question would be whether the oxalate reaction would happen or whether all the peroxide would be used up in other reactions. I've been playing with botanical cyanotype toners and with some of them you can visually see the liquid change color when exposed just to air. Annette Golaz says that higher pH promotes oxidation in the toners, so plays more of a role than just converting prussian blue.

Yeah, in alkaline medium, tannic acid gets de-protonated (-OH to O- and H+) making it more prone to oxidation, changing color. It also tones faster and as I have noticed, tends to stain the paper more as well. So it's better to keep it neutral to slightly acidic.

:Niranjan

 

[Raghu Kuvempunagar]

My first attempt didn't go well but the mistake is mine only. I underestimated the exposure thinking it would be very short like Cyanotype Rex. I'll try again sometime later with generously more exposure.

 

[nmp]

My first attempt didn't go well but the mistake is mine only. I underestimated the exposure thinking it would be very short like Cyanotype Rex. I'll try again sometime later with generously more exposure.

Why not do an old fashioned step wedge to figure out the exposure.

:Niranjan.

 

[Raghu Kuvempunagar]

The idea of using coffee dicoction yesteday was not a good one - it produced a very pale image. Today I gave another try with Haritaki and it worked a lot better. Haritaki produces good black tones in the print and the toner also turns black within a couple of minutes. Apparently Haritaki contains Tannic and Gallic acids.

BTW I noticed that Peroxide bath turned yellow-brown very soon - probably indicative of Ferric Oxalate getting into solution.

 

[NedL]

... BTW I noticed that Peroxide bath turned yellow-brown very soon - probably indicative of Ferric Oxalate getting into solution.

That makes sense!