tomhumf Posted March 18, 2020 Report Share Posted March 18, 2020 See image attached. I've never seen anything like this before but last two firings I've had it on 2 different glazes. It occurs are the same spot in kiln ( at the base opposite burners - this seems to be a colder spot. ). I'm firing a very small gas reduction kiln. The bubbles are super thin and crack if you touch them, underneath the glaze seems to be melted fairly well. The only thing I can think I changed on last two firings is I added a neural / oxidation phase near the end this has got the top of kiln up to temperature better. Also maybe my bisque has been a bit short... So any ideas what's caused it, and if you think refiring them will smooth over bubbles? Link to comment Share on other sites More sharing options...
liambesaw Posted March 18, 2020 Report Share Posted March 18, 2020 If you're adding oxygen at the end it may be uncombusted carbon or sulfur in the body or glaze that is able to suddenly combine with oxygen to make carbon dioxide or sulfur dioxide which expands and escapes. That's all I can think of if that's the only change. Link to comment Share on other sites More sharing options...
Mark C. Posted March 18, 2020 Report Share Posted March 18, 2020 Grind them flat and refire-a dremel tool with a carbide bit works great for this. was the fire a short(fast one) or a long glaze melt which tends to lay bubbles down Link to comment Share on other sites More sharing options...
tomhumf Posted March 18, 2020 Author Report Share Posted March 18, 2020 2 hours ago, liambesaw said: If you're adding oxygen at the end it may be uncombusted carbon or sulfur in the body or glaze that is able to suddenly combine with oxygen to make carbon dioxide or sulfur dioxide which expands and escapes. That's all I can think of if that's the only change. Right. I'm wondering next time whether to try body reduction - neutral/ ox phase then back into reduction...or just live with top firing colder than bottom. 49 minutes ago, Mark C. said: Grind them flat and refire-a dremel tool with a carbide bit works great for this. was the fire a short(fast one) or a long glaze melt which tends to lay bubbles down Ok ill try that. It was around 8 hours glaze firing so not super short for my little kiln Link to comment Share on other sites More sharing options...
tomhumf Posted March 18, 2020 Author Report Share Posted March 18, 2020 I'm just remembering when I glaze them, a couple of them were really bubbly on the surface, which I smoothed over. I think the top of my bisque was a bit underfired , possibly where these mugs were so maybe this has caused it... Link to comment Share on other sites More sharing options...
Babs Posted March 18, 2020 Report Share Posted March 18, 2020 Tom roberts adviced me to crush/ grind bubbles, apply a dab of glaze then refire with a soak to even kilntemp Link to comment Share on other sites More sharing options...
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