Can anybody tell me if toxic oxides used as inglazes (applied to glaze surface before firing) remain harmful after being taken to 9 or, for that matter, any stoneware temperature? Not for food use, of course, but general handling. In this particular case I am concerned about a pot we made with large areas of vanadium pentoxide decoration. Before washing, these areas were quite dusty, presumably, with cooked vanadium. The glaze is a kaolin and ash mix with copper carbonate and iron oxide additions. Thanks Pete
Oxide Toxicity
Sep 09, 2003
5 Replies
In a word - YES. Toxic oxides stay toxic no matter what temperature they are fired to. After firing, the question becomes whether the glaze is stable enough so that the oxides don't leach out. What you've described as your glaze is almost certainly far from a stable glaze. Certainly, if the pot came out the kiln "dusty" it is not a stable glaze. As the robot on "Lost in Space" was fond of saying, "Danger, Will Robinson, Danger!"
deg
Thanks deg, I thought as much. I take this to mean that the only safe in-glaze decoration will be with iron, rutile , ilmenite and commercially available food-safe products. Does the same go for on-glaze and lustre finishes as virtually all lustres are toxic? Pete
Using non-toxic (or nearly so) oxides is the safest way to go unless you are sure that your glaze is stable and not leaching excessive amounts of the oxides. The only sure way to know this is to have your glazes leach tested. You can find more info on glaze stability and info on where to get your glazes test at
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Even some commercial glazes leach more than they should. Some can show a color change just by having a lemon slice left to sit on them.
deg
deg
Yes Deg, you're right, definitly. In fact, here in Italy, is strictly prohibited to use vanadium pentoxide, no matter which glaze you're using on your ceramics.
Have a good day!
Luca
For your interest the following is taken from the UK Health & Safety Data Sheet for Vanadium Pentoxide (MSDS)
Section 15 Regulatory information
EC Supply Labelling T Toxic Dangerous for the Environment R(Risk)-Phrases R20/22 Harmful by inhalation and if swallowed R37 Irritating to respiratory system R40 Possible risk of irreversible effects R48/23 Toxic: Danger of serious damage to health by prolonged exposure through inhalation R51/53 Toxic to aquatic organisms, may cause long term adverse effects in the aquatic environment. R63 Possible risk of harm to the unborn child S(Safety)-Phrases S13 keep away from food, drink and animal feeding stuff S20/21 when using do not eat, drink or smoke S22/23 do not breathe dust or spray S36/37 wear suitable protective clothing S38 In case of insufficient ventilation wear suitable respiratory equipment S45 In case of accident or if you feel unwell seek medical advice immediately (show label where possible). S61 Avoid release to the environment. Refer to special instructions/ safety data sheet
Steve Bath UK
In article , snipped-for-privacy@ceramicadamore.com writes
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