Eric Suchman on wed 9 oct 02
I was wondering if any one could tell me if the amount of barium in this
glaze fired to ^10 would be considered food safe?
Custer feldspar 40
Colemanite 20
Barium oxide 05
Talc 08
EPKaolin 05
Silica 15
Zircopax 08
This was used as a white liner glaze at a college I went to.....'liner' in
that it was for lining the inside surface of food ware.
Thanks in advance
Eric in Oceanside
John Weber on thu 10 oct 02
For your information here are the results of GlazChem for your glaze. I
would think the Silica is a bit low (limits are around 3.0 to 5.0) but I
personally just wouldn't use barium in a liner glaze. If I was compelled to
use it then I would have it and all of my liner glazes with anything suspect
in them tested by a lab. This glaze uses Barium Carbonate, I don't have
Barium Oxide in my database, and it used Gerstley Borate instead of
Colmanite with no change in amounts from you recipe.
Na2O 0.07 Al2O3 0.27 SiO2 2.45
K2O 0.01 B2O3 0.40 P2O5 0.00
MgO 0.37 TiO2 0.00
CaO 0.43 Fe2O3 0.01
MnO 0.00 ZrO2 0.21
BaO 0.12
Alumina:Silica ratio is 1.00:8.93
Neutral:Acid ratio is 1.00:3.97
Alk:Neut:Acid ratio is 1.00:0.67:2.67
Expansion: 64.1 x 10e-7 per degree C
Oxides causing abnormal expansion:
B2O3
Ric Swenson on thu 10 oct 02
BaO3- some would zero is safe. the "acid "test is "Is the material soluble enough to be leachable into food?" I recommend you send a piece or two of the pottery, intact, to a test lab and specify leachability for foods of heavy metals...lead, barium, cadmium etc. (US TEST LABS ?)
IMHO, there is more danger to YOU...so use common sense in handling Barium Carbonate.
As I remember..vaugely, as I approach my geezerhood... there was a single nasty report early last century of some British soldiers becoming ill when a baker, who happened to be a non- english reader, mistook barium carbonate for flour and cooked up some biscuits that gave all who partook a serious case of 'sick', and actually killed one older officer. Other than that, when I researched it in grad. school in 1976 at Univ. of Puget Sound, I found very few incidents of barium poisoning... at that time. Perhaps others have more current information to share?
A Barium Sulfate 'milkshake' is, I believe, still taken internally for radiology studies of the intestinal tract in humans..... and yet other forms of barium have been used in history as a rat poison?
HTH.
Regards,
Ric Swenson
Fine Art Tile
San Antonio, TX
Paul Lewing on thu 10 oct 02
on 10/9/02 5:37 PM, Eric Suchman at esuch@EARTHLINK.NET wrote:
> I was wondering if any one could tell me if the amount of barium in this
> glaze fired to ^10 would be considered food safe?
Eric, I'm sure several people will tell you there's no way to tell for sure
whether this is food-safe or not without professional testing. But I did
want to make a few points in addition.
First, no one really knows whether glazes containing barium are "food-safe"
or not, because there's no standard definition of "food-safe" to start with,
and no one is really sure of the effects of leached barium anyway. So far
the assumption that leached barium oxide would hurt you is an educated
guess.
Second, have you ever tried this glaze without the barium carbonate? I'd
bet you wouldn't even notice if you just left it out. Try it. If you
notice any difference at all, I'd bet you could restore it by adding a bit
of whiting
Paul Lewing, Seattle
Ron Roy on fri 11 oct 02
Hi Eric,
The total fot his glaze is 101 including the zircopax - am I playing with a
full deck? Just want to konw if I have all the right numbers and
ingrediants.
Looks like it might be OK - you will only know about the durability if you
have it tested.
There is no reason to have any Barium in a white glaze by the way - no
advantage at all and you are paying big bucks for an expensive carbonate.
Sub in 3.5 strontium for the 5 Barium and you have the same glaze but the
expansion is a bit lower.
Sub in 2.5 whiting for the Barium and you still have the same glaze - an
even lower expansion and whiting is a lot cheaper than either Barium or
Strontium.
RR
>I was wondering if any one could tell me if the amount of barium in this
>glaze fired to ^10 would be considered food safe?
>
>
>Custer feldspar 40
>Colemanite 20
>Barium oxide 05
>Talc 08
>EPKaolin 05
>Silica 15
>Zircopax 08
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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