|Monthly Tech-Tip |
Yes. Ancient Copper, as of Nov 2023, it is no longer available. Right is G3948A, our iron red (a publicly available recipe). Both of these have been fired using the C6DHSC slow cool firing schedule. As you can see the PC-56 crystallizes more, matting the surface in the process. But if cooled normally (e.g. using the PLC6DS schedule) it does fire similar to G3948A. Likewise, G3948A can be made to crystallize more if the iron oxide percentage is increased in the recipe (we use black iron, it is a little less concentrated than red but does not gel the slurry). The recipe offers excellent slurry properties when mixed as a dipping glaze. Our version uses Spodumene (which has 7% Li2O). Of course, lithium materials are very expensive these days, but that is what is needed for this effect. If you make a brushing glaze of it using our instructions only about 70g of spodumene is needed to make a 500ml jar. At current material costs, we could make 3 jars for $10 worth of powdered materials!
This is the G3948A recipe fired to cone 6 using our standard C6DHSC schedule. The color "breaks" to black where thinner around contours so it seemed like a natural that the inside glaze should be G3914A Alberta Slip black. The contour of the foot ring is important or the glaze will run onto the kiln shelf. My standard fluted ring foot is working well. Perhaps a better option would be to glaze the bottom inch or so with the black as a catch glaze.
This is G3948A (similar to the popular Ancient Copper product). To get this stunning result it needs to be applied thickly. Therefore it runs a lot. But the catcher glaze on the bottom cm of these mugs has stopped the flow. The catcher is a glossy black glaze and is hardly noticeable. I use G3914A as the catcher but Amaco Obsidian would also likely work. The inside glaze, G2926B, is one I have tested and developed to fit our clay bodies really well.
Iron Red Glaze
A type of ceramic glaze, typically fired around 2200F, where iron oxide in the cooling glass precipitates out to form a striking red crystalline mesh on the surface.