Valeria Posted June 10, 2022 Report Share Posted June 10, 2022 Hi, I was wondering if you could help me understand why the wood ashes created that opaque patina in the centre of this bowl and if you think a refire could help. I mixed unwashed dry ashes to a neutral glaze I regularly use and thickly brushed the mixture on the thinly glazed bowl you can see in the picture, fired to 1260C on my previous tests I only had shiny crackled amber glass where the ashes where most concentrated. I know that with unwashed ashes surprises are to be expected and I also welcome them, but I would be curious to understand the possible causes thank you Valeria Quote Link to comment Share on other sites More sharing options...
Mark C. Posted June 10, 2022 Report Share Posted June 10, 2022 That glaze is thick and pooled in bottom and crazed badly Refireing will most likely just thicken the glaze in bottom and craze more both are bad or worse than it is now This is true with most temperatures cone 5-6 or cone 10 whatever Quote Link to comment Share on other sites More sharing options...
Valeria Posted June 10, 2022 Author Report Share Posted June 10, 2022 Hi Mark, thank you for your reply. I am just trying out with some thick wood ash concentration because I cannot yet invest time in making a proper wood ash glaze. I am learning really… Do you think that that patina is just because of the thickness of the glaze? I have tried on other small cups and the results are not food safe but beautiful looking. At least to me You can see the test in the photo thank you again, Valeria Quote Link to comment Share on other sites More sharing options...
neilestrick Posted June 10, 2022 Report Share Posted June 10, 2022 The opaque area could be crystals, or it could be an overload of calcium from the ash that's not taken into the melt. Quote Link to comment Share on other sites More sharing options...
Valeria Posted June 10, 2022 Author Report Share Posted June 10, 2022 Thank you Neil! This is useful, I thought it could be just an unmelted situation or something else more chemical that I cannot yet recognise do you think I should just leave alone this testing? And make a proper ash glaze? Any more insight would be appreciated Quote Link to comment Share on other sites More sharing options...
neilestrick Posted June 11, 2022 Report Share Posted June 11, 2022 4 hours ago, Valeria said: Thank you Neil! This is useful, I thought it could be just an unmelted situation or something else more chemical that I cannot yet recognise do you think I should just leave alone this testing? And make a proper ash glaze? Any more insight would be appreciated It's not that it didn't melt in terms of heat, but rather that there's too much calcium for the glass to take in. And that may or may not be the situation. It could just be crystal growth. Making a proper ash glaze would probably be a better way to go IMO. Adding ash to an existing glaze can certainly work, but there's also a chance it's just going to throw it so out of whack that you run into issues. Take a look at the unity formula of ash glazes and you'll see that they are really high in calcium, and really low in silica. On paper it looks bad, but they work. So if you take a typical glaze that is high in silica and also dump a bunch of calcium (ash) in it, things can get out of whack quickly. Unwashed ash, with all the soluble ingredients, can further complicate things. Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
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