Thursday, July 8, 2010
Mixing underglazes and art glazes
A question from another ceramic artist had me thinking about the different kinds of glazes used in making decorative pieces like medallions, pendants and beads.
For realistic colored horses, the process used here at the studio is pretty straightforward. The horses are airbrushed with a combination of both opaque and transparent underglazes. Details are added using a combination of erasing, etching and handpainting with transparent underglazes. Afterwards the horse is fired with a clear (usually gloss) glaze.
Giftware that isn't realistically colored, like the medallions that are often used for awards at shows catering to ceramic horses, are done in what are known as "art glazes". Art glazes are designed to "break" over the high spots of a design, so the color is paler there, and then pool in the recesses.
This Christmas ornament I did for my (non-horsey) family and friends a few years ago shows the "breaking and pooling" effect really well. The tiny pendants from the previous post were also done with art glazes. (The one that was done in green and blues used a blue glaze which was wiped off the high spots and then painted over with a pale green glaze so that the high spots would be green instead of pale blue.)
There is also a third kind of colorant that falls somewhere between a true underglaze and an art glaze. It gives a flat, opaque color like an underglaze, but unlike traditional underglazes it bisque fires with a hard, often semi-glossy finish. True underglazes are extremely matte, almost chalky, after firing. Often these kinds of underglaze - which are marketed under the names Stroke & Coat (Mayco) and Concepts (Duncan) - are easier to find than traditional underglazes, which is unfortunate for anyone wanting to do the kind of underglazing used for ceramic horses because they don't behave quite the same way.
They are, however, extremely useful in combination with traditional underglazes when backgrounds are involved. The dapple grey Arabian pendant above (the original 1.5" version of the piece that was shrunk in the previous post) had a background done with Concepts.
The tiny bit of blue background under the horse's jaw on this medallion was also done with Concepts.
The bay Celtic Pony at the beginning of this post, and the pinto one that decorates the blog header, were done with traditional underglaze (the ponies), art glazes (on the backgrounds) and Concepts (the bridles).
Over the next few days I will to explain when and why I use art glazes and Concept-type underglazes, and why something other than traditional underglaze is needed for this kind of project. I will also show how I get underglazed finishes to "play nice" with art glazes - or at least how I tilt the odds in my favor that they will play nice!
at 8:14 AM