Highfire Stoneware


Highfire stoneware is a ceramic of clay, silica, fluxes (which help the other ingredients melt), and grog (coarse particles which add "tooth" or strength to the wet clay), which is fired to ~1300 deg. C (cone 9-10).  The key feature of stoneware is that the clay particles melt to the point of fusion with their neighbors, resulting in a strong and durable piece.  Porcelain is similar to stoneware, except it has no grog, and contains white-firing clays.

Covering most pieces is a glaze, which is similar to stoneware except it contains no grog, much more flux to help it melt, and colorants.  Colorants are typically oxides of cobalt, iron, copper, or chromium, mixed into the glaze in very small quantities.  Upon firing, the glaze melts into a viscous liquid, which then cools into a colored glass.  Often the color is not very predictable—after a firing, the opening of the kiln is often an exercise in dropping expectations and cultivating appreciation!

Most of my work is made by throwing (on the wheel) or slab construction (flat pieces of clay joined together with liquid clay).
 

Here are some examples...


 Candlesticks: cobalt/iron colorants for base, second glaze
with titanium sprayed in center. (approx 5" tall)
 


Plate and Soupbowl: black iron and titanium colorants for base,
talc and spodumene (lithium spar) glaze painted in circle. The base
glaze bubbles up through the white glaze.


Serving bowl: two layers of glaze (a spodumene/talc white on a cobalt blue).
(approx. 11" dia.)


Slab vase: the black color in this case comes from layering white
and black clays and rolling out the sandwich, then scraping off
the top layer to bring out the contrast.


Dinnerware set: Cobalt and iron oxides for base, a spodumene/talc white glaze
sprayed on top, which goes into the mottled pattern upon firing, probably because
of surface tension effects. Thickness of the white glaze is critical,
and difficult to maintain. Closeup of the cup is below, to show mottling:


(see above)