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Everything posted by yedrow

  1. John, that was very informative. I'm referring to the size change that occurs during kiln cooling and during use, in an oven for instance. I may be all wrong about the terms I'm using. It wouldn't be the first time. As I understand it, the clay and glaze will shrink to the maximum loss in size at the maximum heat-work they experience. Then, as the materials cool they will contract. In this case, COE would be seen as -COE, or coefficient of contraction. At room temperature then they will expand and contract relative to temperature change and if they get very (~400 f.) hot they will experience however much of a crystobalite bump the body possesses. Also, if the glaze has a greater COE than the clay, it will craze, if a lesser COE it will dunt. Given both are excessive enough to generate a sufficient differential. Isn't that what it means when Insight lists COE? If not, please explain since I'm totally confused Joel.
  2. Ben, by failure I mean shivering, dunting, crazing, etc. John, I understand. I need to know the COE of the body I'm using. My supplier doesn't have this information. I'm guessing I'll have to extrude some bars to get a ball park figure and go by that. This is really probably not very doable without a dilatometer reading of both the clay and the glazes. I was drawing inferences from what I took to be an average set of glaze COEs, from original sources. Is there any value to drawing such inferences? I don't think I can afford dilatometer testes. But, that being said, if I only had the clay tested perhaps I could. I guess my main question would be that range of acceptable COEs, `6.5-7.8, good for a rough draft on a glaze designed in Insight? Joel.
  3. I have always used melted wax in a skillet. I dip work with flat bottoms and I paint it on footed ware. I've tried the sponge method but there were problems (not coming to mind at the moment). Wax resist has never worked well for much of anything to me. I use it when I have no other choice. I'm very interested in trying the damp carpet trick though, thanks, Loretta! Joel.
  4. Since this came up in another thread... How does COE work in a relative sense? I understand the dilatometer sense. But the COE of one glaze relative to one body doesn't seem to have the same effect as the COE of another glaze on the same body, at least as far as failure goes. Am I correct? I've been looking at glazes that are within Insight or in the Roy/Hessleberth book and I find what seems to me to be a pretty wide range of COEs. I've been assuming that a COE of ~7.8 (Insight) to be the upper limit, and ~6.5 to be the lower limit. Is this even close to right? Joel.
  5. Thanks everyone, I think I'm going to give the Roy glaze a try this week (the one from the book). I'll have to look to see where I put the tile from the presumable 'Roy' glaze. If I find it I'll take a pic and post it. It wasn't a cone 6 glaze I'm pretty sure. Joel.
  6. I'm a firm believer in dealing with the problem as early as possible when it comes to clay. Like 'oldlady' said, use a rubber rib to burnish the bottom. After that, there is a green wheel for the Dremel that works quite well on small imperfections. Joel.
  7. I do what should probably be called quasi-production. I don't make only one thing, I make several different items and often three or four different things in a day. I throw around 35 to 40 one pound mugs in an hour, around 18 pie plates in an hour, and around 18 three pound spoon jars in an hour. I throw between 100 and 150 pounds of clay in a day. I hand make my handles. To do this I roll the clay into a ball, then without changing much of the motion, I roll it into a carrot shape. Then I slap this down to flatten one side and then cut off the tip of the big end. I wet both the mug and the big end and attach the handle. I can do this in about the time a person using an extruder takes, when doing a run of 30 mugs. After 30 mugs the extruder starts getting faster. But, if I'm doing 10 mugs I'm much faster. All total it takes me about 4 minutes to throw, trim, and handle a mug. Repetition is the trick. On top of that, I'm a form guy. I have no interest at all in a well glazed pot if it doesn't have good form. I follow a simple set of rules I learned from a Ferguson quote, "First learn technical skills, then form, then the kiln/glaze, and finally surface." Most of the work I've seen ignores the first two parts and goes straight to glaze and decoration. But to me, to get the beauty out of a pot, you need the form. Form comes from control and control comes from practice. Just make lots of pots. And, if you can, find a good handle and try to reproduce it. I think I have a good handle, here is a pic. Feel free to give it a shot. Another couple of tips: Good handles come from a good eye for negative space, and let yourself flow, like water. Beauty comes from natural motions in an analog sense, not from digital skips and jumps.
  8. Anyone have a ^6 black recipe that is reliable in that kiln-to-kiln way? I've tried a couple off the net, including one that had Ron Roy's name on it, and they were less than acceptable. Would anyone care to share a nice glossy black in trade for my humble appreciation? Joel.
  9. yedrow

    September '13

    Some work I did in September.
  10. Thanks guys, that was extremely helpful. That chart was great Peter! I was kinda getting it, then Biglou posted that link with perfect timing. By going back to the Seger formula on paper I saw the relationship between the alumina and silica to the fluxes as numbers. Thanks again. Joel.
  11. When using my glaze calc. software I've noticed that I can raise my Al/Si without it affecting my RO numbers in the unity formula. Granting that I will ultimately go out of my limits, outside of those limits is there a rule of thumb about the relationship of fluxes to non-fluxes? Joel.
  12. I don't think you can buy Kona f-4 anymore. I believe Minspar is now its replacement, but I'm not sure how exact that replacement is. Joel.
  13. You could get a copy of, "Mastering Cone 6 Glazes," by Roy and Hesselberth. They have very reliable ^6 glaze recipes in there with pics that in my experience are almost exactly what you will get out of the kiln. From those recipes you can pick a glaze and purchase exactly and only the raw materials you need in the quantities you want. I don't know the numbers but I suspect you would be spending only a fraction of what it cost for commercial glazes. On top of that you would also have very well explained information that is essential for getting good results out of a ^6 kiln. Joel.
  14. I just watch to see how wet the surface gets and judge my thickness from that. Joel.
  15. Well now I just feel silly. I swore I had looked for this in the Hammer's dictionary. Seriously, I could see it in my mind. Thanks for the help. Joel.
  16. I'm with you Jim. The Soldner is the best wheel I've ever thrown on by a huge margin. And, the Griffon Grip is a skill killer. I however have yet to see any value to hard clay beyond early retirement, lol. Joel.
  17. Please excuse me if I've asked this before, but, can anyone give me a good definition of 'free silica'? I'm thinking that it is silica in a clay body that isn't a part of the Al2 2SiO2 2H2O molecule. Is that right? Joel.
  18. Humor aside, are there montmorillanites in Sagger? Joel.
  19. I think Bailey is a good company. However, I've used their wheels and their pugmills and from those experiences I've concluded that the engineering behind their products is geared towards a narrower definition of the device than is appropriate for what I do. It is like they got ten pottery magazines and averaged the most common complaints/expectations of the device and then engineered from there. Theirs tools don't seem to be so much build around the job being done as they are built around commonly held expectations. Joel.
  20. I tend to have different needs than most potters it seems, so you can take what I say with a grain of salt, but... I like the Brent because the pedal is a little lower and for production work, to me, a pedal that is closer to the floor means less fatigue. The Baily's pedal is pretty thick. I don't like the splash pan since it makes it difficult to make some of the production items I make. I prefer a removable splash pan since I prefer more versatility in a wheel. Though not my first choice, to me the Brent is a professional machine, a rare item in the pottery world. I will say that the Bailey is pretty quite and isn't a bad wheel. And, I think that $700 is kind of pricy for the Brent, especially with the drive.
  21. Great advice everyone. The one I use at work has hundreds of pounds of clay a day run through it. But the one I get for home will not be used for weeks at a time. I really appreciate the advice about putting a damp sponge on the end and keeping the chamber as empty as possible. That will prevent me from likely having had to learn that the hard way. Joel.
  22. How often do you clean out a pug mill, in pounds of clay probably. And... How hard do you pull down on the handle? I put quite a bit of force on it, but I'm not absolutely certain that is necessary. Thanks, Joel.
  23. Thanks everyone! Mart, I'll use it to pug clay for my studio. Joel.
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