If I sound a little weirdly poetic, my apologies - I'm just always astounded by how much copper (and other colorants) can move during the firing process. Have you ever cracked a glaze kiln and noticed that the glaze on one piece has seemingly cause the glaze on a different piece to blush, or turn a different color? Yeah, that's not just in your head -- that's pretty much exactly what happened. And copper, it seems, is a particularly guilty party to this. Here's a great sample that we just pulled out of a kiln that demonstrates just how intense blushing can affect your glazes:
They were so much alike, until the tile on the right had a run-in with some errant copper.
So believe it or not, the two tiles posted are the exact same glaze - The Ceramic Shop's Cotton Candy, to be exact. This is a light pink translucent glaze - but that's clearly not what the tile on the right has going on. THAT tile was placed next to a copper-heavy glaze test in the kiln, and it caused enough blow-off during firing that copper deposited on the surface of this tile, reacting as the green colorant that it is, overpowering the pink colorants and turning the whole test a pretty decent shade of green. Kind of shocking how legit this looks - like a classic celadon! However, if that is NOT the look you're going for, blushing can be quite the surprise when you unload your kiln. A note about the firing -- these results occurred in a Cone 6 electric firing, but blushing can easily happen in reduction firings, too.
Avoiding this effect is pretty easy, though -- if you have any green glazes, make an effort to fire them on a shelf together. Light- or white-colored glazes, as well as translucent and transparent glazes, are particularly susceptible to blushing, too, so just keep those away from their over-friendly coppery counterparts in a kiln and you should be all set.
Just as we love to see examples of your work with our glazes, we also love to see your weird experiments and glaze tests, too! Got any good blushing stories? Send them along as we'll post them on our FaceBook page.