This pot licking keeps coming up. Gotta admit, I have never licked a pot. It is a confusing issue for non-potters and apparently potters as well. Granted, if you tongue sticks to the unglazed portion of a pot, it is much too absorbent to be durable, particularly for freeze and thaw cycles. But vitrification has nothing to do with a pot being low fire, mid fire or high fire. Vitrification is dependent upon the clay body itself. A low fire clay is intended to vitrify at cone 06, about 1800 F give or take. Mid-fire clays, as in stoneware and some newer porcelains is cone 6, a bit over 2000F, and hi fire 2300+ and more.
A low fire pot can be vitrified, but the pot is softer and low fire clays generally have a higher absorption rate, so they are less durable in freeze / thaw and all other ways as well. You can't simple fire a low fire clay higher to give it the qualities of a mid or hi fire clay as the clay body itself matures at a lower temperature than those. I have seen the results of this mishap in kilns I have rebuilt and kilns that were completely ruined when the low fire clay becomes molten and you are left with a big solidified glassy glob as a solidified puddle in your kiln.
Other than paint your own pottery studios, most studios will not allow low fire clays. Some have learned the hard way, and others by example. Many times some one would offer me some free low fire clay, but I will not allow it in my studio. It is not worth the risk.
Conversely, a clay body designed for high fire, cone 10 will not fully vitrify in a cone 6 firing. This is also likely to suffer in a freeze / thaw cycle, but at least it wont destroy the kiln.
With experience, one can tell the difference between low fire and mid or hi fire being as it is denser and heavier. Also there are visual indicators like color flashes which are usually apparent on reduction gas firings and wood firings which almost always fully matured hi fire.
. The best way to be able to tell the difference is to actually see as many bonsai pots as you can IN PERSON. Simply picking a good one up one can typically tell if its high fired from the heft, glass-like finish--most high fired pots will "ring" if tapped on the side. Lower fired pots tend to "clunk" when tapped.
, from my grandfather.. but my mother donated it to a WW2 collection.
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