I'm not currently a ceramics artist (though upon reading, this about mixing glazes is fascinating) but rather I'm exploring wood ash chemistry for an upcoming "Waste Not" workshop at our farm in Western NC - these workshops are about diving deep into applications for what is conventionally considered a waste product. I'm admittedly in over my head a little with this one.
I've stumbled across a brilliant green (with a touch of blue) color after soaking wood ashes that have been calcined for 2 hours at 1500F. What is causing this?
Some details of the experiment:
I have two samples repeated 4 times. One sample is presoaked wood ashes - soluble compounds have been removed for making potash 'lye' water. The other was not yet soaked.
Each 1 cup sample was roasted at 1500F for over two hours.
The presoaked, calcined ash was soaked again with water (in an exploration of portland cement alternatives) and the excess water was clear and very alkaline.
The un-soaked, calcined ash was soaked w/ water revealing almost instantly a brilliant green color in the excess water.
I've had soil application tests that reveal each soaked and unsoaked sample have similar amounts of Mn and Cu... two elements I suspect would attribute to the green color but are not necessarily soluble in water.
Is it that I've oxidized the copper and therefore somehow made it soluble? and that only a very small amount (135ppm dry, 165ppm soaked ash) is enough to change color that dramatically?
My plan is to decant and recrystallize what's in this small amount of vibrant green water. Exercising the normal precautions - glasses and gloves - should I be otherwise concerned?
I'm asking the ceramics glaze as I suspect what I've stumbled on was perhaps some kind of middle ages technique someone here may be familiar with? I understand that in your craft, impurities in the glazes can have a huge impact, and I know wood ashes have a role in some glazes. Is this particular case at all relevant to your work?
Thanks for reading