Glaze materials
The local rocks provide a wealth of material for glaze experimentation and development. The Blue Biddy schist is particularly interesting, and easily obtainable by picking up from the side of the road in a cutting through the outcrop. This rock is quite soft, making it easier to crush. It contains a modest amount of iron and a large amount of silica, which lends itself to softer colours in the glaze making. It is currently giving a lovely blue celadon in small quantities and an attractive opaque jade green celadon in larger amounts.
I also use a shale from a pit at the Mudgee brickworks. This is a dark grey, oily looking rock, which is quite high in mica and contains much more iron than the schist. It is also much
more fusible, as evidenced in the quite vitreous red bricks that it was originally used to make. I currently use it to make a mid-tone, transparent green celadon with a good development of fine bubbles in the glass matrix.
Among the other rocks which are useful for glaze material is a phonolite from Bald Mountain near Rylstone. This is a hard, dark igneous rock which is high in iron and silica (the name phonolite refers to its ability to ring when struck with a hammer). A small amount of this rock in the glaze provides the iron for the opalescent blue Chun glaze, and larger amounts are used in the darker glazes.
Wood ash provides another useful addition to some glazes. Due to the variability of it’s nature, I don’t use it in the celadon glazes, but it is a necessary ingredient in the Chun glaze. My current ash supply comes from two sources; one is a softwood ash (mainly pine) which came from a clearance of Radiata pine from the local natural bush habitat along Jamison Creek, which runs below the pottery (Radiata pine is a proscribed weed in this area). My other source of ash comes from my fireplace, and is ultimately a mixed ash, predominantly hardwood.
I have developed an Ash glaze, using my collected fireplace ash of the last three years. This proved to be an unusual glaze, as the mixed ash consists of hardwoods and softwoods, including scrap timbers from the workshop construction. As the ceiling is lined with ply panels and the framing is of treated pine, it is quite possible there may be some odd trace elements in there, including copper...the results produced a dark, at times almost metallic glaze, which I have reserved for use on the lampbase series for Sarah Davison Designs.
2006: the ashes are changing, as the fireplace wood changes, and other sources appear. I currently have a blackwattle ash which has produced a classic green ash glaze suitable for use on domestic stoneware. It is the traditional fluid bottle green glaze that looks good on dark stoneware and is also pleasant on white stoneware, though it remains heavily crazed
2007: The Blackwattle ash has come to an end, and there remains just a bucket of glaze which will carry on for a little while yet. I am obtaining a supply of Yellow Box (hardwood) ash, which should fulfil my requirements for those glazes that have an ash component
for further information and ongoing ashes, see the section on Ash Glaze