Michael D Posted July 9, 2020 Report Share Posted July 9, 2020 I’m curious why, above and around certain tiles, in closely stacked shelves, there is a clear brown halo. The glaze in question has among other things, strontium, lithium and copper carb in it. It’s clearly coming from just that glaze. Any knowledge on this and if this should be a health concern? (I run a venting fan during the firing.) thanks. Link to comment Share on other sites More sharing options...
Min Posted July 9, 2020 Report Share Posted July 9, 2020 Looks like copper fuming. How much copper carb is in the recipe? Do you have kiln wash on the shelves? It's hard to tell from the image, is this the underside of a kiln shelf? Link to comment Share on other sites More sharing options...
liambesaw Posted July 9, 2020 Report Share Posted July 9, 2020 I get this from soluble salts too, my clay is full of them and some of my glazes too. At least that's what I thought it was. Wouldn't imagine copper would fume under the vessels where it's unglazed Link to comment Share on other sites More sharing options...
Min Posted July 9, 2020 Report Share Posted July 9, 2020 I read "above and around" to be, well, above and around, not underneath. Link to comment Share on other sites More sharing options...
liambesaw Posted July 9, 2020 Report Share Posted July 9, 2020 2 minutes ago, Min said: I read "above and around" to be, well, above and around, not underneath. Oh whoopsies, I get those marks UNDER my stuff. No clue then! Some fairly nasty stuff comes out of a kiln during firing, hydrochloric acid, hydrofluoric acid, sulfuric acid, heavy metal vapors. Link to comment Share on other sites More sharing options...
Mark C. Posted July 9, 2020 Report Share Posted July 9, 2020 The chemical glaze fumes leave marks-heat flow leaves marks-hard to tell which it is -even clay bodies leave marks (especailly stonewares) If you have a vent no big deal. About a heath concern ,well pottery can be a concern but if you read up on it and take steps like venting outside-controilling dust -wearing gloves while glazing etc you will be fine. I would not put the studio in the kitchen for example. Link to comment Share on other sites More sharing options...
Michael D Posted July 9, 2020 Author Report Share Posted July 9, 2020 4 hours ago, Min said: Looks like copper fuming. How much copper carb is in the recipe? Do you have kiln wash on the shelves? It's hard to tell from the image, is this the underside of a kiln shelf? Yes. you are looking at the underside of the shelf just above (no more than 1" above) the tiles with the glaze that copper and other ingredients I listed. I hadn't noticed this before and these are new Corelites. The glaze has no more than 2% cu in it. Maybe a chemical reaction with the new shelves... Thanks Link to comment Share on other sites More sharing options...
Min Posted July 9, 2020 Report Share Posted July 9, 2020 I’ld check the draw on your vent, also might need to have greater than 1” above shelves with tiles (with this glaze) to have the fumes pulled away. Don’t think it’s a chemical reaction with the shelves. See if it gets darker in those areas with your next firing. Link to comment Share on other sites More sharing options...
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