SDBRADBURY@aol.com on fri 2 oct 98
I wanted to know if boric acid and borax are toxic in lowfire glazes (cone 04)
on functional pottery used for eating and drinking. I have tried to search
for this info and I'm not getting to much feedback. Can you help? thank
you.
Tom Buck on sat 3 oct 98
Steven B:
The chances are extremely low that anyone would receive a harmful
dose of boron ion leached from a lowfire borate glaze.
My chem dict says this about "Boric Acid": Hazard: Moderately
toxic in large doses (5 grams for infants).
If by Borax you mean Sodium Borate Decahydrate, then again this
material, used in clothes washing machines, is relatively safe. Farmers
use the Pentahydrate as a weed-killer and soil sterilant, and to control
fungus on citrus fruits ("FDA tolerance is 8 ppm of boron residue"). And
finally, Anhydrous Borax (no water of hydration) is used mainly to make
glass, enamels, and other ceramic products. It is also used as a
herbicide. Although not stated, a hazardous level might be 5 ppm ingested.
Good lowfire glass on a pot would likely be best and safe if the
C06 glaze mix contained 1 mole (+/-) of B2O3 per mole of Flux oxides
(usally CaO + KNaO). The literature suggests that you could have as much a
1.3 moles B2O3/mole fluxes and still make good glass. The corresponding
Alumina would be 0.22-0.25 moles and the Silica would be 2.2-2.5 moles.
Is this what you needed, Steven? Keep well. Tom.
Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).
On Fri, 2 Oct 1998 SDBRADBURY@aol.com wrote:
> ----------------------------Original message----------------------------
> I wanted to know if boric acid and borax are toxic in lowfire glazes (cone 04)
> on functional pottery used for eating and drinking. I have tried to search
> for this info and I'm not getting to much feedback. Can you help? thank
> you.
>
Louis Katz on mon 5 oct 98
Just to add a bit more info to the mix.
High Boron glazes do not hold up well in alkaline environments. Our lowfire
soapdish lost ALL of its glaze on the interior. Another got a good start. Old Py
glassware was easily etched by dishwashing detergent, etc.
It seems foolish to test these recipes in only an acid solution when they are s
soluble in alkalies.
Soapdish recipe:
Gertsley Borate 70
Kaolin 10
Flint 20
The pot was made in around 1977
Louis
--
Louis Katz
lkatz@falcon.tamucc.edu
http://www2.tamucc.edu/lkatz/lkatz/
(512) 994-5987
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