Bob Hamm on sun 30 apr 00
Ray and Janet
Ray wrote
>> because glass *is* a ceramic material.
Janet wrote
>I am sorry, but I do not agree with "glass *is* a ceramic material".
According to A. E. Dodd,s Dictionary of Ceramics, "In the USA a radical
extension of meaning was authorized by the American Ceramic Society in 1920;
chemically, clay is a silicate and it was proposed that the term 'ceramic'
should be applied to all the silicate industries; this brought in glass,
vitreous enamel, and hydraulic cement. In Europe, this wider meaning of the
word has not yet been fully accepted." This reference was published in1964.
As of that date I guess you are both right on your respective sides of the
pond. I wonder if there have been any changes since then.
Ray wrote
>> In fact, glazes are just glasses.
I would agree to a point. A clear gloss glaze is a glass, but a crystaline
glaze is another question. A glass by definition must cool to rididity
without crystalizing.
Bob
Bob Hamm
Super Mud Works
Kelowna, BC Canada
Ph 250 765-8876
Email hamm@direct.ca
Ray Aldridge on tue 2 may 00
At 04:43 PM 4/30/00 EDT, Bob wrote:
>----------------------------Original message----------------------------
>
>Ray wrote
>>> In fact, glazes are just glasses.
>
>I would agree to a point. A clear gloss glaze is a glass, but a crystaline
>glaze is another question. A glass by definition must cool to rididity
>without crystalizing.
>
Good point, Bob. It seems to me, too, that the glazes which prove to be
unstable are more often re-crystallized mattes than glosses. I don't know
if that's a useful generalization, but most of the balanced liner glazes
I've seen are gloss glazes.
Maybe I'm misremembering, but I seem to recall that when I used those
mustard yellow reduction glazes that were so popular in the 70s, that a
broken shard would reveal a dark, apparently glassy layer under the surface
crystallization. Would this be a glass, but with an altered surface?
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
John Hesselberth on wed 3 may 00
Ray Aldridge wrote:
>Good point, Bob. It seems to me, too, that the glazes which prove to be
>unstable are more often re-crystallized mattes than glosses. I don't know
>if that's a useful generalization, but most of the balanced liner glazes
>I've seen are gloss glazes.
Hi Ray,
Your generalization may be more right than wrong--I suspect it is but
don't have enough data to prove it. I do know I have seen unstable
glossy glazes and stable crystallized mat ones. And vice versa of course.
I think mats are most likely to be unstable when they are mat because
they are underfired. Real multiphase mats can be pretty darn stable. I
am convinced that staying within the limits for a balanced glaze
increases the odds the glaze will be stable, but it doesn't assure it.
Likewise I have seen a few very stable glazes that are outside limits.
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"Pots, like other forms of art, are human expressions: pleasure, pain or
indifference before them depends upon their natures, and their natures
are inevitably projections of the minds of their creators." Bernard
Leach, A Potter's Book.
Ron Roy on thu 11 may 00
I read something interesting about this. Essentially it was a discussion
about crystalline glazes and how the crystalls robbed the surrounding glaze
of silica while they were forming. The statement was something like - when
acid etched the crystals became proud - were above the robbed glaze
inbetween them - which means the silica deprived glaze in between the
crystals was short of silica and subject to acid attack.
RR
>----------------------------Original message----------------------------
>>Good point, Bob. It seems to me, too, that the glazes which prove to be
>>unstable are more often re-crystallized mattes than glosses. I don't know
>>if that's a useful generalization, but most of the balanced liner glazes
>>I've seen are gloss glazes.
>Your generalization may be more right than wrong--I suspect it is but
>don't have enough data to prove it. I do know I have seen unstable
>glossy glazes and stable crystallized mat ones. And vice versa of course.
> I think mats are most likely to be unstable when they are mat because
>they are underfired. Real multiphase mats can be pretty darn stable. I
>am convinced that staying within the limits for a balanced glaze
>increases the odds the glaze will be stable, but it doesn't assure it.
>Likewise I have seen a few very stable glazes that are outside limits.
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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