Barbara Long on mon 30 jun 97
A friend is doing some glaze tests and asked if I could call upon the
wisdom of fellow clayartists.This comes from a recipe published in the
12/96 issue of Ceramics Monthly, recipe of Howard Koerth, the ingrediant
in question is Flint Vancil W-20.
Does anyone know where we might find this, or is there an alternate
substance that can be used?
TIA
Barbara in Lyme,Ct.
potluck@snet.net
Barbara Long on tue 1 jul 97
Thanks to Jonathan Kaplan for his response to my question re Vansil W20.
If I was smarter I would have printed it or saved it prior to trying to
respond with a thank you note. I was trying to delete the duplication of
the message in the response...and got carried away with the delete
button. Jonathan, if you see this would you please resend your excellent
reply so I can hardcopy and bring it to my friend.
Thanks
Barbara
potluck@snet.net
Howard on tue 1 jul 97
Barbara... with regards to your question about Flint Vancil W-20:
Vancil W-20 is an R.T. Vanderbuilt trade name for their wollastonite.
Vanderbuilt also produces a Vancil W-10 and Vancil W-30. All three are the
exact same mineral, but the W-30 consists of the finest particle size and
the W-10 is the least fine. Although I have never seen "Vancil W-20" and
"Flint" grouped into one phrase before, I can see how wollastine and flint
have similarities. Wollastinite is Calcium Silcate (CaSiO3 or CaO.SiO2)
while flint is nearly pure silica containing less than 5% impurity in the
form of calcium carbonate.
Howard Axner
Kathy Darnell on mon 19 jan 98
Could someone on this wonderful list please explain the difference, if
there is a difference, in alumina hydrate and aluminum hydrate. I
purchased some aluminum hydrate to use in a kiln wash thinking that I
was buying alunina hydrate. I may want to use alunina hydrate in a
glaze formula if it is one of the ingredients.
TIA James E."Chic" Darnell
Monroe, LA Where the Crawfish season is getting in full swing.
chicdee@bayou.com
Tom Buck on tue 20 jan 98
My chem dictionary says this about the alumina compounds:
aluminum hydrate -- see aluminA trihydrate
Alumina trihydrate (aluminum hydroxide; aluminA hydrate; hydrated
aluminum oxide) Al2O3.3H2O or Al[OH]3.
Properties: White crystalline powder, balls, or granules, density
2.42g/mL, insoluble in water, soluble in mineral acids and sodium
hydroxide (lye, caustic soda). Noncombustible.
So as you see, the two compounds you named are identical, same
chemical, different names, partly because there are two routes to
extracting the compound from bauxite ore.
Also, please note that granular alumina and and granular hydrate
(trihydrate) become the same after one firing... the water of hydration is
removed.
You could use trihydrate in place of alumina (both powders) in a
glaze recipe but you have to account for the loss on ignition that occurs
with trihydrate. Mole weight of alumina, Al2O3 = 102 (two atoms of Al).
And the MW of trihydrate is 78 (with one atom of Al though). Hence,
102 grams Al2O3 is equivalent to 2x78, or 156 grams of Trihydrate. So,if
the recipe calls for 15 grams of Al2O3 you'd have to use 23 grams of
Trihydrate.
Til later.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
Em1312@AOL.COM on thu 25 jan 01
Good morning..........I do much of my clay work at a studio that is part of a
city's Parks and Rec program, so we need to be careful with the funds
available for glazes chemicals.......we still have some Gerstley Borate,
which we find is a part of most of our raku and cone 5/6 oxidation glaze
recipes. We also have about 25 lbs of Colemanite that was donated to the
studio..........we've tried experimenting with the colemanite in raku glazes
and have been unsuccessful, they tend to settle and become solid, almost
impossible to break up......what are we doing wrong? All I've read about
colemanite seems to say that the gerstley is a direct replacement, but it
sure acts differently in our experience. Would you know that floating blue
glaze is an absolute favorite among our students................thank you for
any information.
Em in sunny, but chilly Florida
Kathi LeSueur on wed 8 feb 06
Everything I've ever read about selenium said that it was extremely
toxic and leaches out of glazes. Therefore, I was surprised (horrified
actually) to see red dinnerware which looked alot like copper red) at a
local discounter that was labeled as containing selenium.
I've already written to John H. about this. and would like the opinion
of some chemical people before I approach the company or better yet, my
senator.
Thanks,
Kathi
skiasonaranthropos@FSMAIL.NET on wed 8 feb 06
Hello Kathi,
You may be being a little premature in dashing off to your senator
A typical western diet means up to 0.15 mg are ingested each day. Although
present in many foods nuts are a particularly rich source and selenium
supplements are sold. Selenium is both helpful and harmful: trace amounts
are needed to maintain good health, such as to ensure the functioning of
certain enzymes, but over exposure is a concern and has been associated
with some cancers.
Despite what is too often taught pottery raw materials are complicated; a
typical refined clay sold to potters contains over sixty different
elements, and a little bit of selenium is most likely present. The
materials you are using now will contain some arsenic, lead, barium,
caesium, uranium .............
Selenium may not be as familiar in glazes as Al or Si but it does find
uses. Lead and cadmium are known to potentially present dangers but are
widely used in glazes. Given appropriate use, control and testing the end
user is not in danger, though of course without correct understanding and
tight controls they should be avoided
Whilst I can not pass comment about the safety of the ware you have seen as
with so much in life =93its never that simple=94
Regards,
Antony
Linda Ferzoco on wed 8 feb 06
Kathi,
Selenium is an essential trace element, required for
health, but in very small quantities. In large
quantities (see below) it's toxic. You could say that
about: copper, chromium, manganese, molybdenum and
others. It's the quantity and the route of
administration that make these toxic.
Linda Ferzoco
Caifornia
Here's what the Merck Manual has
Selenium
Selenium (Se) is a part of the enzyme glutathione
peroxidase, which metabolizes hydroperoxides formed
from polyunsaturated fatty acids. Selenium is also a
part of enzymes that deiodinate thyroid hormones.
Generally, selenium functions as an antioxidant that
works in conjunction with vitamin E. Plasma levels
vary from 8 to 25 µg/dL (1.0 to 3.2 µmol/L), depending
on selenium intake.
In a recent study of patients with a history of basal
or squamous cell skin cancer, selenium 200 µg/day
appeared to reduce mortality from all cancers and the
incidence of lung, colorectal, and prostate cancers.
However, it did not prevent the appearance of skin
cancer nor significantly affect all-cause mortality.
These findings require further study.
Deficiency: Selenium deficiency is rare among humans,
even in New Zealand and Finland, where selenium intake
is 30 to 50 µg/day, compared with 100 to 250 µg/day in
the USA and Canada. In China, where selenium intake
averages 10 to 15 µg/day, selenium deficiency occurs
in association with Keshan disease, an endemic viral
cardiomyopathy affecting children and young women in
that country. This cardiomyopathy can be prevented but
not cured by selenite supplements of 50 µg/day.
Patients receiving long-term TPN have developed
selenium deficiency with muscle pain and tenderness
that was responsive to a selenomethionine supplement.
Toxicity: At high doses (> 900 µg/day), selenium
produces a toxic syndrome consisting of dermatitis,
loose hair, diseased nails, and peripheral neuropathy
associated with plasma levels > 100 µg/dL (> 12.7
µmol/L).
--- Kathi LeSueur wrote:
> Everything I've ever read about selenium said that
> it was extremely
> toxic and leaches out of glazes. Therefore, I was
> surprised (horrified
> actually) to see red dinnerware which looked alot
> like copper red) at a
> local discounter that was labeled as containing
> selenium.
>
> I've already written to John H. about this. and
> would like the opinion
> of some chemical people before I approach the
> company or better yet, my
> senator.
>
> Thanks,
>
> Kathi
>
>
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