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thiamant

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  1. Wollastonite being better than whiting because it has less LOI is just a myth... Even at cone 6, cones are designed to measure the last 100 C of the firing for a reason, below that point, they just don't melt. If you can prove (scientifically of course) that a single material melting is going to trap gasses from whiting please publish it and let me know. Common sense tells me that it won't, even if that material is 30% of the recipe, as long as there's room for the gasses to escape (and there is, you can check the article Melting behavior in Traditional ceramics) this shouldn't have any effect on the result. I'm not saying that I'm right and you are wrong.. but I think that some statements should be taken with a grain of salt, because they are not proven, and when you have a problem like the op has, this wouldn't be the first thing I try. So going back to the OP's problem. I see a very strange color in your test tile, did you add a colorant to the recipe that you didn't tell us about? Are you sure your kiln reached temperature (did you use cones)? If you only have problems with this material, have you tried using it in other glaze recipes? Maybe you just got a mislabelled batch (this has happened to me before). Those bubbles really look nasty. Look at this picture from Derek Au (creator of glazy): same glaze... using whiting, no bubbles or pinholes.
  2. I think a single material melting range is not as relevant as the whole glaze melting stage, which only happens in the last 100 C of firing. I have fired the same glazes using wollastonite and whiting, and the result is exactly the same.
  3. In my humble opinion, using Wollastonite instead of whiting wont be of any help at all. By the time your glaze starts to melt all the gas from calcium carbonate is more than gone.
  4. What recipe are you referring to? Anyway, that's why I said that I don't blindly trust COE calculators. As @Min said you can't just compare COE of two different glazes and predict whether it's going to work... I didn't say they were all wrong. Actually test #9 looks pretty promising (as I said it was too thinly applied and it's a bit dry but now that I have a good candidate I can try different thickness). And test #5 seems to work on body 1, which is probably the one I will be using. So having found two candidates is good. I feel I'm almost there. BTW, I don't want to say this loud because prices might go even higher but I just fell in love with spodumene and lithium in general. I used it in another glaze (very different from this one) and it just gives me a perfect melt, 0 blisters, really, that extra kick on fluxing power is a real thing, plus how you can reduce CTE so easily...
  5. From my experience and the real experiments I have seen from different people, usually more than 0.6 alumina and 5.5 silica is going to have a hard time melting. I dont like limits because they Just put a rectangle in there and its not that simple. In reality its more like a curve with different gradations of melting... But thats probably another discussion for another day... I am curious why did you ask? What I wanted to say is that test #9 is probably far from the ideal melt at cone 10, it looks a bit dry but since the application was thin I cant really tell, so I have to repeat this one and probably a couple more with a thicker application to really find the best candidate.
  6. I don't use limits, just Stull, UMF and chemistry, but they are all within green & cooper and Hesselberth & Roy cone 10 limits. Only 6 and 8 are within Val Cushing's cone 9-10 glossy limits. The calculated COE are: 1 - 6.79 2 - 6.62 3 - 6.47 4 - 6.33 5 - 6.20 6 - 6.32 7 -6.27 8 - 6.48 9 - 5.99
  7. So here are the results after thermal shock stress test, I tried to keep my ratios .3:.7 (.15 Lithium .7 potassium .8 sodium) and tried with different silica levels, decreasing silica levels really makes things worse ( I was hoping maybe less cloudiness by doing so, but all tests from 1 to 4 had crazing). Test 5 didn't show crazing on body 1 but it did on body 2. Test 9 had the most Silica and alumina, and didn't craze on any of these bodies. Test 8 is the only one that didn't have .3:.7 because it's just g1947U minus the zinc. So it actually has .17:.83 flux ratio. Looks melted but crazing a bit on body 2 (maybe because of unmelted silica). Test 6 is lying really close to the original g1947U but in this case it is crazing (unlike the original g1947u with the zinc), probably because there are more alkali metals fluxes in it. #9 is on the limit of the melting area (.58 Alumina 4.63 Silica), but it shows the best results. Many of the applications were on the thin side so I will repeat 9 a bit thicker and probably another one with less amount of silica. I could also try more lithium and less sodium, or even .2:.8 with .2 Lithium. Since I'm already really high on the si/al levels, that also means less spodumene and cheaper glaze... I'll see depending on how much time I got... EDIT: Sorry tiles 3 and 4 are interchanged, they do follow the more silica less crazing trend (I placed them wrong in the picture).
  8. I'm going to try 0.15 LiO2 + 0.15 KNaO2 instead of 0.3 KNaO2 and see what happens. I haven't had these foaming problems yet (only used spodumene in small scale).
  9. Unmelted silica has super high thermal expansion, while melted silica is the opposite, super low thermal expansion. How am I supposed to trust this system which is based on unmelted materials?
  10. @MinI compensated the lack of Zinc with more calcium to keep fluxing ratios more or less the same... I never considered adding more calcium would make the glaze craze more. I don't trust the COE given by calculators since they are based in raw materials and not the actual melt that you end up getting, which is quite different.
  11. @Min Ok, so this is my version of the g1947U with grolleg kaolin: https://glazy.org/recipes/163310 (not crazing) This is the NephSy clear with 15% kaolin (also tried with 18% with same results): https://glazy.org/recipes/163307 (crazing) And the zinc version of the nephsy clear is just the previous one with 18% kaolin and 2.5 zinc added. And the spodumene is just https://glazy.org/recipes/164474 It's very little spodumene maybe I should just add more and remove some nephsy while keeping ratios. Yes, These tiles were at the bottom of the kiln next to witness cones, the lower part of the kiln fires a bit lower, so cone 10 went to 3 o'clock, cone 9 went completely melted and 11 started bending. (The upper part of the kiln fires to a perfect cone 10)
  12. Amazingly all the g1947u came out perfect with 0 crazing and passed the stress test... I have spodumene. I guess i could add in a bit of lithium to get to a .2:.8 flux ratio since im slightly below the .2 (just like the g1947u). In fact just adding 2% spodumene i get Is that going to make a big difference? Why is the g1947u not crazing at all? Is it the zinc? The potash feldspar? @Mark C. I dont have ball clay in my studio but crazing is more body dependent so your glaze might work perfect for your clay body and crazy crazing in my clay body...
  13. After the stress tests (150ÂșC to ice water), all the nephsy clears had crazing, the one with the 2.5% zinc added had less crazing, but still crazed a bit. The G1947U with grolleg didn't have crazing. Sooo, all my dreams gone . I'm wondering however why the added zinc made the glaze craze less, since it has less alumina and silica molecules in it...
  14. Sure, will do. It seems very easy. Spraying is nice for me because my studio is very small, I don't want to fill large buckets of glaze until I'm 100% sure that this glaze is ready to use in a larger scale. I've made that mistake before . Meanwhile spraying is very effective, I can prepare a small batch of glaze (100g) and use it for spraying a middle sized bowl or piece. Will let you know about the stress test.
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