I ran a few glaze tests during my last glaze firing. “Raw Sienna” is my favorite glaze from ‘Mastering Cone 6 Glazes’ so I figured I’d play around with it a bit! The glaze is based on Ron Roy and John Hesselberth’s “High Calcium Semi-matte 2” base glaze, with the addition of 6% rutile and 6% RIO. In my tests, I changed the recipe for Raw Sienna by stepping down the amount of RIO, mixing up 3 batches with either 4% RIO, 2% RIO or 0%RIO (the latter is the book’s ‘Bone’ glaze). I tested the resulting 3 glazes on both test tiles (3s dip, the another 2s dip on the top) and on small flat plates (5s dip). Here are the results:

Left to right: 4% RIO, 2% RIO, 0% RIO (Bone)

Left to right: 4% RIO, 2% RIO, 0% RIO (Bone)

Verdict?  We’re not crazy about the bone on my white stoneware (Axner WC-901) and the 4% is fine, but lacks the extra “oomph” (to use the technical term) one gets from that extra 2% RIO.  The 2% RIO is interesting, especially where it thin (bottom of the test tile). It has a lot of rich variation which appeals to me.

What’s next?  Though nice, the 2% RIO is not really different enough from the original Raw Sienna to warrant a full batch mix up.  Next test will be variation of both the RIO (3% this time) AND the Rutile (halved to 3%).  We’ll see what that gives us!


Original Raw Sienna on a small “Shaka” pinch plate