Jeanette Harris on thu 4 oct 07
I got this query from a friend in Canada. She bought the pot in the
U.K. Every time she tries to make tea in the pot, it leaches this
white stuff. It's a new pot, I believe.
I told her to not use it, but I'm wondering what could make this
happen. (She makes tea in the traditional way.)
Photos of the teapot can be found here:
http://catsphotogallery.infohost.no-ip.org/teapot/
Here's what she says:
"As far as i know, this pot was made in England just before the
ceramic house went under.
here is the info that was on the tag"
Cauldon Ceramic presents
brown betty tea pot
available in 4 sizes
2 cup, 4 cup, 6 cup and 8 cup
in brown Rockingham glaze
crown clarence works
clarence road
stok-on-trent, staffordshire
st3 1az england
Our brown better teapots are still made from teracotta as used by the
elder brothers in 1965. their methods of making was by "jollying" but
in later years it became "slip cast" giving a smooth finish and even
thickness. rockingham brown glaze complies US FDA and California
proposition 65. the pots are microwave proof and heat resistant."
Thanks for you help.
Jeanette
--
http://jeanetteharrisblog.blogspot.com/
http://www.washingtonpotters.org/members/Jeanette_Harris/wpa_jeanette_harris.htm
Jeanette Harris
Poulsbo WA
Ivor and Olive Lewis on sat 6 oct 07
Dear Jeanette Harris,
You ask <in the U.K. Every time she tries to make tea in the pot, it leaches this =
white stuff. It's a new pot, I believe. I told her to not use it, but =
I'm wondering what could make this happen. (She makes tea in the =
traditional way.) >>
Terra Cotta is a porous body and the patterns suggest the glaze is =
crazed. It would have to be crazed on the interior wall as well. So =
fluid is going to seep through. It may be that the original clay was =
contaminated with Sodium chloride and this is what is making the white =
deposit. Or it could be Calcium Carbonate Lime which changes to oxide =
during firing then to hydroxide when that dissolves into hot water.
The original Rockingham Ware was made in Swinton, near Rotherham where =
the city museum has a wonderful collection. The original glaze was Lead =
Manganese.
Since the company has gone out of business there is no recourse to =
compensation. I suggest it is polished and used as a collectors item.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Charles on sat 6 oct 07
My best semi-educated guess is that these are lime
deposits from extremely hard water along the craze
lines. I also have extremely hard water and every now
and then the ceramic bowl we use for the cats will get
a buildup on the around the full water line and
continue down to the bottom of the bowl. We found a
soak of vinegar loosened it up enough to clean it with
the rest of the dishes.
Best wishes,
Charles
Visit me on the web www.hughespottery.com
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Donald Burroughs on sun 7 oct 07
Hello Jeanette
The stuff leaching from that Brown Betty is probably alkalines from the
terra cotta body reacting to the tannins found in teas. From your images
it looks as though that BB has seen better days prior to the glaze firing
(glaze fit issues?) or if it looked fine before use it may suffered some
sort of thermal shock? I have a really nice stoneware mug form which was
made by one of my past profs.. Recently, I tried to use it and poured hot
espresso into it and I heard a thuding cracking sound when the hot liquid
filled it. Not wanting to lose the attractive form, I immediately poured
out the espresso. There are no visual indicators of any physical trauma to
the mug,I concluded that while the glaze was attractive and looked to fit
well to the form, there must be an issue regarding thermal expansion and
contraction (glaze to body) that was not discovered post firing. Then
again maybe the mug's surface temperature was cool enough (we try to keep
the house temp. as low as possible) that it reacted with the hot espresso
in such a way as to cause the reaction I spoke of. Of course hot espresso
is hotter than regular coffee/tea, but I have other handmade mugs which
handle hot espresso just fine. By the way those images with your
reflections and the crazing are way cool in of themselves. You should make
sure to author/copyright them.
Don
Ivor and Olive Lewis on sun 7 oct 07
Dear Charles=20
Your suggestion that this problem is due to the use of "hard" water has =
merit.
This may be true for the drinking water you provide your animals. But if =
the hardness is due to Calcium or Magnesium Bi-Carbonate in solution, =
boiling water for Tea removes these two substances by decomposing them =
and precipitating Calcium or Magnesium Carbonate, usually referred to as =
"Furring". However, if the hardness is permanent due to Ca or Mg =
Sulphates these would be retained in solution after water was boiled for =
the Tea.
Best regards,
Ivor
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