lisa skeen on thu 13 may 04
Heehee....just opened a box with the donation to the Belize trip fund =
from Ilene Mahler. Man o man does she make some mighty fine crystalline =
work! Now, I like to look at crystal work, but usually can't afford it, =
and so I have no idea what to tell the customer in terms of care. Can =
they go in the dishwasher? (I'm guessing no.) I'm also guessing since =
crystals are by definition cracks in the surface of the glaze, that =
they're not for wet food. Somebody correct me if I'm wrong. What about =
microwave?
Thanks
L
L. P. Skeen www.living-tree.net
Living Tree Pottery, Summerfield, NC
"There are three kinds of men. The ones who learn by reading, and the =
few who learn by observation. The rest of them have
to pee on the electric fence."------- Will Rogers (att.)
Ron Roy on sat 15 may 04
Hi Lisa,
I don't know about the likelyhood of crazing between crystal and none
crystal glaze - I have never read anything about that. I tend to think it
must be true - at least in some cases but that does not necessarily limit
use. If the ware rings when the rim is hit - then it is not crazed.
Crystal glazes - (big crystals) - the crystals take silica from the
surounding glaze so it might be that the surrounding glaze would wind up
short of silica - so it might be unstable.
If there are no toxins present - you just have to worry about that glaze
going dull after repeated contact with acidic foods.
Cryalline glazes can be very short of alumina (runny) so they will probably
be unstable in the dish washer and change over time.
The microwave part - if the clay is vitrified properly and does not absorb
water the ware should be OK - but if the glaze is short of silica - heating
acidic food on it will elevate the rate of acid attack.
I would tend to think OK for food and microwave (if the clay does not
absorb water) but not for the dish washer.
If I had the recipe of the glaze I can make a more educated guess.
RR
>Heehee....just opened a box with the donation to the Belize trip fund from
>Ilene Mahler. Man o man does she make some mighty fine crystalline work!
>Now, I like to look at crystal work, but usually can't afford it, and so I
>have no idea what to tell the customer in terms of care. Can they go in
>the dishwasher? (I'm guessing no.) I'm also guessing since crystals are
>by definition cracks in the surface of the glaze, that they're not for wet
>food. Somebody correct me if I'm wrong. What about microwave?
>
>Thanks
>L
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on sun 16 may 04
Dear Ron,
There seems to be some great gaps in our knowledge of the science and
technology of Crystalline glazes. We are well versed in the folk craft
of the art but when it comes to answering questions I think we are
left wondering.
Rationally it would seem that as the crystals for they deplete the
melt of Silica, as you suggest. This would promote and increase in the
ratio of Alumina. So the glaze might begin to increase its viscosity.
I think there needs to be more thought about these questions.
Best regards,
Ivor Lewis. Redhill, South Australia
Fara Shimbo on mon 17 may 04
Hi, Ron and Lisa,
Regarding putting crystalline bowls in the dishwasher,
I do it all the time. Just as an experiment, one day when
a plate broke in half, I put it half in the dishwasher and
put the other half aside. I kept the half in the dishwasher
there through 100 washings just to see what would happen. I
have the two halves in front of me and to be honest, I couldn't
tell you which half was the one in the dishwasher. I don't
remember which was the half I put in, and the two are exactly
alike in color and texture. (I used my own Bory 1 glaze and
White Stallion porcelain. This mixture doesn't craze.)
I've also set crystalline ware in the microwave with lemon
juice in it and microwaved it until the juice boiled away.
There was a discoloration in copper-colored wares but not in
anything else.
Nevertheless.....
I always tell people crystalline glazes are not food safe.
Not because I'm worried about bacteria but because I'm worried
about litigation. People are so paranoid and over-reactive
these days I wouldn't trust 'em. Let folks who can afford
their own lawyers make dinnerware. As for me, I eat off my
crystalline stuff all the time and if anything has happened
to me because of it ... well, who'd know because I was loopy
as a loon to start with.
Hang in there,
Fa
--
=============================================================
Fara Shimbo, Master Crystalliere, Certified Public Nuisance
-------------------------------------------------------------
Shimbo Pottery, PO Box 41, Hygiene, CO 80533 USA 720.207.5201
Crystalline-Ceramics.Info ShimboPottery.com Crystallieri.Org
Klysadel.Net TuranianHorse.Org
=============================================================
Ron Roy on fri 21 may 04
Hi Ivor,
I am not guessing about this - there is some discussion of the situation in
Ceramics Glaze Technology - Taylor & Bull.
See the chapter on chemical resistance.
During phase separation, changes in composition take place and one phase
becomes more durable ..........
If the examples are acid etched the less durable phase will lose more and
the more durable phase will lose less. This leaves the more durable phase
thicker (proud.) My understanding is that the crystals are the more durable
because they have more silica - and the amorphous stage between the
crystals less durable because they have less silica.
I'm am sure it is more complicated than that and there are probably
exceptions. What does seem certain - if you have multiple phases in a glaze
they will always have different degrees of durability - at least to
chemical attack - and different degrees of hardness as well.
We can also safely assume they will have different CTE (expansion) rates.
I think you are right - there are huge gaps in our (potters) knowledge of
the science of our craft. The texts we normally gravitate towards assume we
don't really want to know. I'm not sure who is at fault in this - the
potters or the authors.
There are signs that this situation is being somewhat remedied - we are
beginning to see some of the crucial information being published - along
with the visual spice we all like to have included.
RR
>Dear Ron,
>There seems to be some great gaps in our knowledge of the science and
>technology of Crystalline glazes. We are well versed in the folk craft
>of the art but when it comes to answering questions I think we are
>left wondering.
>Rationally it would seem that as the crystals for they deplete the
>melt of Silica, as you suggest. This would promote and increase in the
>ratio of Alumina. So the glaze might begin to increase its viscosity.
>I think there needs to be more thought about these questions.
>Best regards,
>Ivor Lewis. Redhill, South Australia
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ivor and Olive Lewis on fri 21 may 04
Dear Ron,
Thanks for your message.
I regret that Taylor and Bull does not seem to be in any of the South
Australian Libraries.
I am coming to think that, in the case of Zinc Crystal Glazes, we
would get a better idea of what is happening as far as the carrier
fraction of the glaze is concerned if the proportions of Zinc oxide
and Silicon dioxide responsible for the Willemite crystals were
subtracted from the recipe. I am sure such information would enable us
to make a better assessment of the situations that occur.
When you come to think about Progress these are the sorts of things
which should be clarified in texts such as Hamer and Hamer. It will be
interesting to know if that happens.
Best regards and enjoy the weekend.
Ivor Lewis. Redhill, South Australia
Potters Council Member
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