Posted by Hideo Mabuchi

This week we shift our focus to a new surface sample, taken from a piece by Dan Murphy (Utah State University).  The clay is a high-iron stoneware body and the piece was wood-fired to cone 8 and reduction cooled.  Today’s featured image shows a close-up of a typical surface feature on this piece — a “splotch” of brighter red-orange color sitting on a darker purple-black background.  Looking at the piece by eye, areas with a high density of this sort of splotch have a bright red tone whereas areas without them appear darker, tending towards black.  Today’s featured image was taken with a DSLR camera with a macro zoom lens; starting next week we’ll look at optical and electron microscope images to reveal the fine structure of this feature.  Dan and I began studying this and other similar samples last July; we are planning a continuing research program that will utilize both the surface analysis facilities at Stanford and the ceramics facilities at USU.

The high-iron reduction cooled surface is quite different from the high-fired porcelaneous “hexagons” surface that we have discussed over the past couple of months.  There is no glassy matrix and we did not need to use acid etching to reveal the micro/nano-crystalline structures that we will show in upcoming posts.  The images raise some intriguing questions about how iron crystals form in cone 8 reduction-cool firings, and whether there could be drastically different physical mechanisms of color formation in firings that stop at cone 8 versus firings that continue to cone 10 and above…

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