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LeeS

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  1. That's a good idea, I wasn't sure how to approach figuring that out. I'm going to see if Clay Planet will sell a half-pound of lithium carbonate as well, otherwise I'll order some online.
  2. Ah ok, I was pretty unsure, it's quite different than most of the other materials I have. All the Pier glazes have a noticeable amount more bubbling/orange peel. I'm wondering if it has additional flux (to achieve transparency) that is interacting with the glaze. Yup, I did all the tests one after another. I also made 250 g batches so everything should have been pretty consistent between tests. Yeah, I think most of my next round of testing is going to be around improving G0027. Maybe small additions of spod will help with lowering the expansion without creating this paradoxical effect in a lot of the other higher lithium tests?
  3. I got a tiny bit of froth, but I didn't need to pre-wash it. Surprisingly little froth compared to what most people describe. The texture is a bit weird too. It's very free-flowing (total opposite of wollastonite), and somewhat granular. Quite similar to table salt. I'm wondering if maybe I used too fine of a screen and it got caught? That doesn't make a ton of sense though because I probably would have noticed before I rinsed my screen off. Next time I'm at the community center studio I'll ask the tech there to see his spod. I really appreciate the offer Min, but don't worry about it. I'll keep working through this and let you know the results :). Of course you're always welcome to try for curiosity's sake, and I would love to know what you get!
  4. First, pictures: https://imgur.com/a/hGDpkE2 I tried to take them at an angle that would show the surface texture, and I embedded some ink in the crazing in some of them. I don't have lithium carb because my local supplier charges $55 for 1 lbs :/. I could try petalite maybe? Or another supplier or just suck up the money? I'll explore this a bit more. 120 F/hr from 2150 F -> 2350 F, then 20 minute hold at 2350 F. ~500 F/hr before that. It provided some useful characterization within the same flux group for sure, as Min mentioned. There was some inaccuracy as the principle fluxes changed substantially (adding/removing zinc for instance). I would say I had useful results within +/- 0.2 COE. Once I figure out if my spod is actually spod or if it has enough lithium I'll give you a better answer :).
  5. All my tests came out of the kiln yesterday with somewhat surprising and mixed results. One shelf was an ideal ^10 and the other was a little over. I also ran a 300 F :: Ice Water test to check for crazing, and all the results below are after that. I'll itemize it to make things easier to follow: [modification from base glaze in brackets] G1947U Based Glazes (1) G0023 [lithium] -- Crazed badly. Progression showed that larger portions of G0023 actually increased crazing against the base glaze. Silica progressions (3% and 6%) showed poor melting and increased crazing. (2) G0024 [magnesium] -- Crazed slightly. Progression against base glaze showed it helped, but it is already starting to matte and stiffen the melt substantially. (3) G0025 [boron] -- Didn't craze on glacia, crazed slightly on pier. This seems like the best of the G1947U based glazed, but it took a ton of boron to melt. I ran a progression from 0.1<->0.2 boron and only the 0.2 melted well and didn't craze. Less boron crazed more. CMW Low Expansion Gloss Based Glazes (4) G0026 [lithium] -- Crazed slightly on the glacia, none on the pier. This is a weird one because the crazing is opposite of everything else on the two clay bodies. The surface is also pretty awful, lots of little half bubbles but it's not properly matte. (5) G0027 [boron] -- Didn't craze on any clay. I ran a progression from 0.1<->0.2 boron as well. The 0.1 boron has the best surface character and is well melted. The 0.2 is a bit bubbly and coarser. Misc (6) G0020 (Ceramic Arts Lithium B) -- Crazed worse than I've ever seen. I didn't even thermally stress this one because it was so bad already. May make a fun crackle glaze? Some interesting results here: The lithium seemed to make the crazing worse in all cases. I'm not sure how to explain this given it's reputation for making low expansion glazes. G0026 on the pier is a bit of a weird exception, but it's an awful glaze visually and to the touch. Nothing is as glossy as G1947U, but I'm somewhat ok with that. Super high gloss isn't really the goal. G0023 definitely couldn't take more silica, at least not 3% more. For future testing, it seems like adding boron is the only option that's working for me. The low boron (0.1) version of G0027 actually feels like the best bet right now, other than the not awesome surface texture. I'm probably going to try a few things: G1947U with both boron and magnesia additions, but not as much extra silica/alumina. G1947U with both boron and lithium additions, probably not as much silica/alumina. G1947U with both magnesia and lithium additions, probably not as much silica/alumina. G0027 with small changes to improve the surface texture. Not quite sure what yet. G0027 with small amounts of lithium (0.05). I'm happy to post pictures if anyone is interested in any particular glazes. It's just a bit much to do all of them and still see the surface well. I would love a bit more guidance on what to try next. I may use the 0.1 boron G0027 as-is, but it could use some improvements and I'm willing to do another test fire.
  6. It's probably not that important and wollastonite is for sure annoying, but eventually I would like to fire very fast (the goal is ~5 hours from cold to ^10) so it'll probably matter more at some point. Of course, the best way to fire faster would probably be to switch to a lower temp... but that's a problem for another time...
  7. Bumped the zinc to 2.5. I'll try the silica progression for sure. Yeah, the LOI is quite low, no carbonates to decompose. It's from the dolomite. If it works out I'll try to switch it for talc and adjust the wollastonite/silica to suit. I just don't have much talc on hand right now. Agreed, it's not a great recipe. This was just the closest I could get to the original with the materials I have right now, but understood it's a big-ish change... The plan was to run it essentially as a control against the modified versions (G0026/27), because they also use potash instead of soda spar, but I'll drop it if I run out of test space in the kiln. Good tip. My tiny kiln cools super fast so this won't be a problem, but I'll make sure not to program a down-ramp. Great tip, I've heard about that happening but didn't know how to deal with it. Ah interesting way to test. I'll try that for sure, because I generally glaze pretty thin and wouldn't notice if the glaze was under too much compression unless it was obviously shivering. I can't thank you enough Min, this has been such an enormous help. Your guidance and explanations are invaluable.
  8. Here are the new recipes based on the G1947U. Swapping out CaO for MgO (G0024) was surprisingly successful and didn't take a huge change to the original chemistry. The CMW mag gloss was a bit more tricky because I didn't have any soda feldspar on hand, so I reformulated it with custer first, to make G0021. I also had to add some dolomite to fix the MgO/CaO ratio which changed with the feldspar substitution. Both new recipes ended up with a bit more CaO, which isn't ideal in terms of testing, but hopefully will result in a glossier glaze. I also shifted them to a slightly higher Si:Al ratio. G0026 attempted to have a similar flux/Al/Si ratio, while G0027 added boron and then significantly more Al/Si. All oxides are fairly well within limits except for MgO. I'm not as thrilled with these because they ended up a bit further from the original chemistry, but they are reasonably inside the limits at least. I also found a lithium glaze on ceramic arts which looks interesting: Here are all of them plugging into Glazy: I still haven't decided how to do the testing. I have ~20x test pieces each of two different clays, one with much lower expansion than the other. I'll probably try some progressions between the original glaze and each of my new attempts...
  9. Wow Min, that cleared up a ton. Especially how to keep similar R2O:RO ratios, it didn't occur to me to swap fluxes within the same periodic group. For my experiments, I started with the CMW mag gloss and the G1947U gloss. Here is the general flow: (note this is with my Insight code numbers to avoid writing out the full name, and COE's are in []'s) I tried to heed your advice to only swap one thing at a time as much as possible. (recipes in next post because I'm out of space)
  10. Yeah, this is the problem. My basic clay/silica progressions stopped melting before they fixed the crazing. I got close for the higher expansion of the two clays (Glacia) but the lower expansion (Pier) is still crazing really badly. I could (and probably will) try again with a glaze with a more durable flux ratio, but again, I don't think I'll be able to get there without a fundamental change to the chemistry. The glazes that get close also fail badly in a 300 F:ice water test, so there is much room for improvement. Will do! It'll probably be a few weeks but I'll drag this thread back up. I'm bisquing ~40 test pieces today! Yes, so far I have good alignment between the calculated COE and the actual crazing. This would be a different discussion if I was a production potter and fired glaze loads more frequently, because I could use a much more iterative approach over several firings. But for now I need to get as many useful trials into one kiln load as possible and using COE as a guide seems to be the best way to do that. On that note... Does anyone have recommendations for how to substitute fluxes? Is starting with 1:1 molar a good choice? Would the same advice apply to boron or do I need to treat it differently? Obviously testing is the most important, so I'll try some progressions of whatever method I use, but any kind of starting point would be appreciated.
  11. Very cool, thanks! Haha yeah, glad I'm not crazy. Ah great find. Somehow missed that in my glazy digging. Without modifications it calculates out to 6.2 COE, so it looks like a good start. Good advice. I'll try this with each of my 'flux' attempts. I don't have access to 3249, or any other MgO frits (I'm sure I could get it, but the local supplier doesn't stock it). I think I might formulate something along those lines with 3124 and talc though. If this all works out I might order a magnesium or lithium frit to experiment with. Haha, I was afraid someone would ask. There isn't a good answer, and I'll probably switch to ^6 at some point. But for now the firing cost isn't significant, and my tiny kiln has no problem reaching ^10 with power to spare. I do have a few reasons why I started there, the main one being I learned at ^10 because that's what the local community centre fires to, so it seemed like a comfortable starting point. Also, my work is slipcast translucent porcelain, and my local supplier has the most selection of ^10 porcelain clays. Last, I wanted to formulate my own glazes, and more raw materials melt at ^10 so it was a bit easier to learn the chemistry.
  12. Would you be willing to share an example recipe? No worries if you would prefer not to of course. I'm struggling with a starting point because most people say you don't need boron at ^10, so there isn't too much info about it. So far I think I'm going to give all three suggestions a shot. Adding alumina + silica to a basic ^10 recipe, adding Li2O in varying amounts, and using a boron frit. It's easy for me to make up a ton of tests, not easy to fire a bunch of times.
  13. Thanks everyone for the help. I see your point about the flux ratios, but I'm having a bit of trouble understanding how to get good flux ratios but low expansion. Low expansion seems to mean dropping as much of the KNaO as possible, but that also drops the flux ratio out of the 0.2:0.8 range if taken very far. Am I missing something here? I know boron isn't needed at ^10, but cost isn't really important here so I was thinking a boron frit could provide a bit more flexibility for adjusting melting in my base recipe. One other thing I noticed is a lot of ^10 potters are firing in big gas kilns with long cycles and soaks, so lots of "^10" glazes don't seem to melt particularly well until the bottom of ^11. That's fair, but unfortunately can't fire that often, so I think it's a valuable starting point. I use it mostly as a method to guide my testing, not the end-all. Thanks Min! Do you change KNaO for Li2O on a 1:1 molar basis? Or just aim for something close and adjust with testing? Would you prefer Li2O over boron? I use Insight. Your pictures are familiar haha :).
  14. Hi all, I'm working on some porcelain pieces with Clay Planet's glacia and pier porcelains. However, I'm having a lot of trouble with finding a glaze to fit. So far I have tested a few starting recipes, all around 6.5 - 6.8 calculated COE. I was most happy with this one: However, all the tests crazed. Predictably, the glazes closer to 6.7 COE were a bit worse than the 6.5 glaze. From there, I tried reducing KNaO and CaO and increasing zinc, silica, and alumina: However, this also crazed badly on the Pier and moderately on the Glacia, and is slightly undermelted (slightly matte, didn't flow well), so it feels like a bit of a dead end. I was hoping for some help with figuring out what to try next. I'm thinking of starting with a boron-fluxed glaze to get some more room to play with melting, something like: I would drop much of the dolomite to reduce MgO matteness, and increase the boron (probably with a frit replacing the gerstley) to correct the melting from removing dolomite, and increase silica and alumina to reduce expansion. Is that a good idea? Is it possible to just improve the one I already have? If anyone has some low COE (5.0 - 6.0 range ideally) glaze recipes they're willing to share I would be grateful as well.
  15. Quick update. I stopped by Clay Planet again today and they were super helpful. They're going to test out the glacia, and they hooked me up with a bag of Pier to try out. We'll see how it goes!
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