More testing completed... and more confused than ever..
I mixed four variations on the previous recipe - two with a little betonite added, and two with OM4 - trying to stop the leakage that occurred with the last test. I made two identical pinch-pots from each, bisqued them all - then fired at ^6 one glazed, one un-glazed of each variation. Then did 24hr soak + 2hr boil on the un-glazed
Mix (balance 'dug clay' approx 40%) Absorption EPK 35, Flint 15, Spar 8 +Bent 2 1.47% EPK 35, Flint 15, Spar 10 +Bent 2 1.47% EPK 34, OM4 3, Flint 15, Spar 8 5.88% EPK 32, OM4 3, Flint 15, Spar 10 5.88%
I filled all of the glazed pots with water & set them on a paper towel. Two leaked, and two did not. In less than an hour, there was water on the towel under two of them - and the water level in the pot was noticeably lower. The other two had no water on the towel several hours later.
Herei's where I get confused: The two that tested at < 1.5% absorption unglazed are the ones that leaked. The pots that tested over 5% absorption unglzed are the ones that did not leak. (No chance I mixed them up... each pair of test-pots was clearly marked as they were made.)
The glaze (floating blue) looks great on all four - no visible pinholes, crazing, etc. I'm not really surprised, based on the absorption tests, that two of them leaked - but I would have expected it to be the two with the higher absorption. Apparently I've still got a lot to learn.
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