John Baymore on sun 12 sep 99
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(snip)
was rather alarmed by the string on shinos. I understand we will be
provided with shinos and slips, but there has been no mention of glazes.
Since some of my pots are functional, I am now rather
worried about the inside of these pots. If I understood correctly from the
various posts, shinos might not be foodsafe or practical as liners.
(clip)
Thought I'd add my two cents in on the =22Shino isn't a good liner glaze=22
thread that seems to be developing.........being a potter who has been
actively selling shino on the insides of functional pots as well as doing
wood firing for 30+ years.
While there certainly are so called =22shino-slips=22..... most shinos you =
see
ARE glazes. High surface tension glazes.... but glazes none the less.
As to the =22foodsafeness=22 of shinos........... on a relative scale of =
things
they are pretty far down the list as glazes to be concerned with. I'd be
more worried about cobalt leaching out of deep blues. Shinos certainly
are not even in the same LEAGUE as the leaching of barium out of copper
laden barium matts.... and in another galaxy from the leaching of lead and
cadmium compounds.
This is mainly because they don't contain much of anything that is
particularly toxic. Most of the shino components are in Monona's roster of
=22if you gotta make a glaze..... these are the oxides to use=22 list. Most=
of
the oxides in the melt are very =22safe=22. (Nothing is perfectly
=22safe=22....... watch out for dihydrogen oxide ....it can kill you if you
breathe too much =3Cg=3E.) The most toxic component of American-type shinos=
is
the lithium oxide coming from the usual spodumene addition. The mol equivs
of this oxide in shino are usually pretty low in the formula also. So
while the glaze might leach some lithium...... it probably would be very
minimal. (Test your glaze to be sure of the exact amount.)
Lithium leaching out of shinos might (and that is a BIG conditional
=22might=22) be a concern to someone already taking close to toxic doses of
lithium as a medication for bi-polar disorders...tiny segment of the
population......... but for the rest of us....... the amount we'd be
exposed to probably would be considered insignificant.
(Lithium leaching out of some of the formulas of other types of =22glazes=22=
I
have seen is another story....and could be a significant issue.)
If you don't want the lithium leaching question..... use a shino that is
closer to the true Japanese one. (I do.) Historically, Japanese shinos
have NO appreciable lithium above trace level in them. (American shino is
to Japanese shino sort of like American raku is to Japanese raku. =3Cg=3E)
As to the crawling.......... let it crawl. Viva la crawling. That is part
of the character of shino glazes. They crawl and pit so nicely. It is
over stoneware... and the body is pretty much vitreous to start with. (If
you use an open body... the raw exposed clay might be of more concern.)
This brings up the whole =22is unglazed clay safe to use for
food=22............. and =22is crazed glaze safe to use with food=22 debate.=
In
my book..... the hazards are certainly there when compared to perfectly
fitting industrial-quality glazes fully covering the body.... but the risks
are so small that they are acceptable. We still use somewhat porous food
preparation and serving utensils all the time....... cutting boards, pizza
stones, wooden salad bowls, wood rolling pins, cheeze cloth strainers, rock
guacomole stones, and so on. Life would certainly be safer without any of
them.... but far poorer. Each person has to decide about acceptable risks
in life a bit.
One control on this situation is that those who do not like the crawled or
pitted nature of the shino as a liner glaze will not buy the pieces. They
will see the glaze as =22defective=22. Which in fact...... it is =3Cg=3E. =
Long
live shino defects=21
In my estimation, I don't think shinos in general are a class of glazes
that are worth a huge amount of worry over toxicology before we look at
far, far more significant issues routinely in use by potters. At Sunapee I
was right near a potter that was selling functional casseroles, platters,
covered jars and the like covered inside and out with blue barium matt
glazes. Now THAT I have a bit of concern with in light of the current
knowledge of the possible problems with barium leaching compounded by the
presence of copper =3Cwg=3E.
Bet I've started a divergent thread =3Cg=3E. Hope it's NOT about barium =
again
=3Cwg=3E.
Best,
....................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752
JBaymore=40compuserve.com
John.Baymore=40GSD-CO.COM
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