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Last semester's soda firing was a huge success!  That's about 12" tall and 17" across, B-Mix fired to just under cone 11 with a D'Arvor kaolin based flashing slip.
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Sep 7, 2014 17:23
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| # ¿ May 14, 2024 10:25 |
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Recent works unloaded from a cone 10 reduction firing.  
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Nov 5, 2015 09:19
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ToxicSlurpee posted:Nicely made. If I wasn't so drat broke I'd offer to buy a mug. Are those celadons? Thanks! The liner glaze is a base glaze and the blue/green surfaces are the same base with oxide additions, 3% iron for the celadon green and .2%cobalt + .2%chrome for the blue, I wouldn't really call the blue a celadon because it's not iron based. I believe the places where the blue starts to blush up into a pinkish color is caused by chrome concentrations reacting with the tin in the base poopcup fucked around with this message at 20:59 on Nov 7, 2015 |
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Nov 7, 2015 20:53
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ToxicSlurpee posted:I think it's more the tin by itself, really. I have a copper/tin colored glaze that gets pinkish chunks in it whenever I fire it in particular ways. I haven't figured out exactly what causes it but I mostly fire to a bit under 9 with very heavy reduction. If I fire it a bit high or it's closer to the fire it can get pink in it sometimes. The same glaze without the tin has never, ever done that. Getting a touch of pink from the tin like that would make sense. How much tin is in the base glaze? There's 5% tin in the base, not quite enough to opacify it but in soda it'll flux to a nice white, tin looks much better than zircopax in my opinion but the cost difference is hard to justify. It's all fired to cone 10 in moderate reduction and soaked for 30 min in an Olsen 16cf. My last firing was just slightly uneven so I didn't get a full cone 10 soak up top and a lot of the wares had very small pinholing in the liner, hoping that a refiring will fix that. I've also reformulated the glaze to lower the expansion by swapping out calcium carbonate for wollastonite to source the CaO for fluxing and increasing the clay ammount from 5% to 9%. The ware has been crazing for over 5 days after unloading them, even now I'll hear a ping every so often and it's been 2 weeks almost. I don't mind the crazing on the exterior, but I'd really like a stable liner that's fitted to my clay body even though the fluidity of the glaze unchanged is really what i want for the exterior and how it interacts with my surface decorations. And it's been kinda fun teaching myself how to use digital fire's insight-live tool for glaze formulation.
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Nov 16, 2015 00:14
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ToxicSlurpee posted:What feldspar are you using? Calcium and potassium are the things that tend to expand the most. You might want to look for a different flux. You might also want to look into a different liner glaze entirely if you want the inside to be smooth. Certain materials have a ton of potassium (oddly enough I deliberately use a particular feldspar for just that reason but right now am forgetting which is which off the top of my head) and can affect that too. What you want to do is look for the formulas that tell you its expansion coefficient. In any event crazing means your glaze is expanding too much and needs to expand even less. Maybe look at a different flux? The ratio of alumina to silica might also need to be fiddled with. My memory is a bit fuzzy as the last time I did any glaze calc was months ago. Even so reducing the potassium and calcium should give you less expansion. Switching the source but keeping the calcium constant isn't going to accomplish a ton. 45 - Soda Feldspar (I believe I'm using minspar at the moment) 17 - Quartz 15 - Ferro Frit 3134 13 - Whiting 5 - China Clay 5 - Tin Oxide +2 - Bentonite +tsp Epsom Salts And the reformulated batch I'm going to test is: 37 - Soda Feldspar 22 - Quartz 15 - Ferro Frit 3124 13 - Wollastonite 9 - Calcined Kaolin 4 - Tin Oxide +2 - Bentonite +tsp Epsom Salts I've got a noticeable change in the expansion rate base on that, my hope is that keeping the higher CaO level will keep the glaze fluid, but I've also made another reformulation that puts an even spread between MgO and CaO which has an even better reduction of expansion, my only concern is having the raise in MgO start to matte the glaze, but I've read that having boron in the recipe can help prevent that so maybe the frit will prevent that problem. I'm also testing a 1% addition of yellow ochre since I really liked the soft jade color I got from that on test tiles. If nothing else the reformulated batch seems to be much better about not firming up at the bottom of the bucket.
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Nov 16, 2015 08:59
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| # ¿ May 14, 2024 10:25 |
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Second firing of the semester unloaded, a few works from it.     
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Dec 2, 2015 21:45
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