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curt

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About curt

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  1. Wood firing conversations?

    If you are going for reduction effects in your wood firing, particularly reducing the clay body for toasty browns, reds and oranges, then firing to cone 5 in oxidation first will tighten up the body too much. Body reduction really takes place starting at around 800 C up to the point where your glaze ingredients get a good melt happening ( at which point body reduction is pretty much over and glaze reduction begins). Bisqueing to around 1000 C still leaves the body open enough to achieve good reduction effects for most clays. In addition, your clay body will likely no longer absorb glaze slop when fired to such a high level. It will be hard to glaze pots which are essentially already vitrified. Unless your clay body is crazy refractory, then Cone 5 is not really bisque firing - it is more like a full stoneware firing. as someone asked above, are you really talking about cone 5? Or cone 05? Huge difference. If cone 05 then ignore pretty much everything I have said here...
  2. After (below) the silica inversion point at 256C, which can affect clay and glazes and at least in principle needs to be passed through slowly, it really depends on what is in the kiln. For functional ware generally, how hot does the water in your dishwasher get? How hot is the boiling water you pour in for your cup of tea? Your mugs will probably be experiencing these temperatures again and again, so if they can’t hack it there... If it is baking or oven ware, even more aggresssive thermal shock in their future...well you get the point. If large, flat platters I would wait until below 100 C for sure - too much thermal shock (ie, sudden cooling) across the surfaces of large flat things sitting on too hot kiln shelves no good. Particularly, glassy (read inflexible) porcelain bodies are sensitive to thermal shock - open stoneware bodies with more grog and large particles seem to have a bit more staying power, with some thought that larger particles in those bodies terminate micro-cracks before they open up into major splits. For more “robust” work, I asked one veteran potter who was running a community studio this same question and he/she said “how badly do you need the work?” Since they were talking about student work I took this to mean that even quite high temperatures are OK to open at if the work is small and thick, and/or it is likely that the people looking at the work will not be able to differentiate cooling dunts from poor making techniques. In this instance the priority was how quickly the kiln needed to be turned around and reloaded at the end of term. Yes, appalling I agree. Needless to say, I do not put anything larger than test tiles in those kilns anymore. But the relevant point for me was that a kiln can often be opened at quite high temperatures without obvious damage to the work (damage to the kiln may be another matter?), and I have seen amateurs get away with this in seeming complete ignorance on more than one occasion. Since I see glaze crazing as largely a chemistry issue, I don’t think opening early makes this more or less likely unless you are opening at crazy high temps.
  3. Lepidolite

    I agree, and hope John will one day return and continue to contribute, as I value his experience and knowledge greatly. No posts should be deleted from this or any other forum thread by anyone. It is against the spirit of these forums and the free and open sharing of information, both for current participants and (perhaps even more importantly) for the many who will come to learn here in the years ahead. If people regret things they said then don’t say them in the first place. Deleting posts once they are out there is a kind of lie, an attempt to pretend things didn’t happen or weren’t said that we all know were said and did happen. As a community, we are better than that and need to be honest. If mistakes were made, just as in our own ceramic practice, hopefully we learn from them and do better next time. If you think you may have offended someone, a simple PM to apologise goes a long way.
  4. Lepidolite

    I was unaware such a section existed. Have just had a look again and cannot see it. Can you or someone else direct me to it? Again, I was totally unaware of this. Can you tell me where these changes have been posted? Do you mean Jennifer Harnetty? Is this something recent? Again, where is it posted? EDIT: I have seen a very brief statement regarding intellectual property from Jennifer from October 6 under the Forum FAQs, if that is what you are referring to. It does not address the issues that concern me. I know we are well off topic here, but these are important issues which have an impact on how I (and probably others) participate in the forums and I have not seen them addressed anywhere. Maybe I have just missed it, but I have been looking.
  5. Interesting, Mark. Any theories on why this is?
  6. Glazes That Break

    I think the idea with breaking is to get the glaze to run off of high points and corners and into crevices and depressions - without running off the pot. Making a glaze runnier by reducing alumina may well promote breaking, but if it is too runny it just runs off the pot so you can only take this so far. That said, a little bit may work and you may get a satisfactory result. Surface tension and viscosity are related but different. Low surface tension glazes have an ability to "wet" the clay surface to achieve this effect. Many oxides in our materials do both, that is lower viscosity and reduce surface tension, but have different effects in these two regards. Magnesium in particular lowers viscosity as a flux, but has relatively high surface tension (compared to silica, which is kind of the benchmark). Same goes for zinc (high surface tension). See Hamer and Hamer for more on this. If you have zinc, talc or other magnesium bearing materials in your glaze think about lowering them to promote breaking.
  7. Lepidolite

    Too right.
  8. Lepidolite

    When it comes time to give input on the forum terms of service, I have plenty of suggestions I would like to make about how a host of issues are handled, including copyright of posted material, editing of posts, deletion of posts, transparency, etc. However, for the subjects at hand I kind of agree with Joseph. Please let that poor horse go, lol! I think Tyler's intentions re fluorine were good - clearly his focus was on the safety of forum members IMO. Regarding doing business on the forums, I like humour as much as the next person, but I agree that we have to be a little bit careful even if we think we are joking, or that others are joking. It is often hard for folks to communicate the mood or underlying intention of their comments - never mind other subtleties, such as sarcasm - in a written context without a lot of extraneous explanation. It happens all too often that a given reader interprets something the wrong way, depending quite a bit on how their day has gone up to that point.
  9. Lepidolite

    In an electric kiln? At least some I would imagine given that natural convection is probably moving some small amount of new air into the kiln through bung holes, etc., particularly if you fire with the bungs open. And if you have a kiln vent going, well, probably a lot more since there is a constant flow of new atmospheric air being sucked into the kiln. In a gas kiln? I would guess the kiln atmosphere would be seeing much more atmospheric moisture than at room temperature. Fuel needs air flow to burn. Atmospheric moisture is getting dragged into the kiln via both the primary and secondary air intakes along with the gas. And that gas/air mix is flowing in at a goodly clip, which we know since most gas kilns have a small positive pressure inside. I think it has also been established that, chemically, water aids in a reduction firing. One of the reasons a good rainy day always makes for better reduction (or so I am told...)
  10. Glazes That Break

    Agree with Min about those variables, although I would say for breaking the surface tension is probably the most important of things to be looking at.
  11. I find the six o’clock mark useful when I am not sure which cells will melt - or how well - and want to have an ex-post indicator. It also gives some indication of how well the glaze heals over. Every cell on your grids appears very well melted so that is not surprising. In fact I suspect that was kind of the point with the oil spotting (ie, to have very fluid melts) so mission accomplished. So Pieter just to be clear, is there iron in the far left column or not? The range you quote above suggests there is? And it does look like there is from the pics. Just want to be sure. Does this mean that bubbles are forming as the kiln cools? I am having trouble understanding how, on the one hand the glaze is too stiff to allow bubbles, but on the other hand it is fluid enough to heal over? Will think about this some more. I think you are on the right track on this. Corner A (high alumina) is in the good glass region looking at the Glazy chart above. Corner C (high iron low alumina) could be smooth because it is forming a different kind of “glass” due to the iron content which is more much more refractory in oxidation. The way the iron “bubbles” to make the oilspots in every cell on the grid is different to the bubbles formed occasionally by off-gassing of other, non-iron clay or glaze materials. However, returning to corner C, I think the big bubbles there are due simply the massive amount of flux (and barely any alumina or silica) in that corner, probably low-melting flux (?), which is simply boiling and boiling away even long after the more “balanced” cells on the grid have stiffened up, and a lot of the way down as the kiln is cooling. Maybe. I don’t remember if you have posted the specific recipe or not, or what else is in the glaze.
  12. Looks interesting. I can imagine three levels/depths of glaze, maybe cascading down from high to low if the glaze is fluxy, or sticking to three seperate levels if too stiff to run?
  13. NCECA

    I guess it doesn’t really matter where it is (even piggybacking on some other group’s coffee hour! ) as long as there is a specific place and time, and people wearing name tags. Would also say if it was part of someone else’s coffee hour and it was a big venue (cause some of those rooms were really big, with hundreds of people in them) , would help to know which PART of that venue forum members were going to be congregating in. LOL in Kansas City, Marcia and I were at the same pre-conference for days helping fire two kilns which were side by side, but we never actually met until days later at the main conference hotel bar almost coincidentally via mutual acquaintances! To be fair it was a form of controlled chaos at those kilns (4 at once firing over several days!), so maybe that is not surprising. For all I know there were probably several forum members around me at every moment but unless you know them by their real names (as opposed to their “handle” on the forums, you are none the wiser! Lol. And I am guessing that although many people from these forums were in Kansas City for NCECA, I did not meet more than a couple of them. Again, maybe not surprising at a conference with 8000 (?) people, but it does highlight that unless you specifically organise to meet people, at an event of that size and geographical footprint, it is highly likely you will not run in to them, especially if you do not know them in the first place. If you are lucky you might glimpse a name tag as people run from session to session... I am betting none of this is an issue for NCECA veterans, but for NCECA newbies like me it is something to think about it.
  14. I would happily run vertical tiles for every one of the 35 glazes on a standard Currie grid if it were not so much work. I am sure it would lead to the discovery of a bunch of interesting glazes that I am missing now because I do not go this extra step. Alas, it does take extra work - producing blank test tiles, firing them, etc. but the biggest problem I really seem to having even selectively running vertical tests is that my standard 300g corner batches do not really generate enough glaze in the cups to properly dip a test tile later. Also, since the delay between initially mixing up the cups and later wanting to run the vertical tests is often a few weeks, I find I usually have to kind of reconstitute the glazes in each cup to get them the proper consistency. More time, and then if I add a bit too much water, well, now it is too thin. I am thinking I could do a better job of using ALL the glaze in the corner batches into the cups, giving me more to work with in each cup, ie more to dip into with a vertical test tile. Or maybe I could mix bigger corner batches in the first place and have more to work with. Or maybe I could decant the glaze from each cup after mixing into a purpose-made, perfectly-fits-the-shape-of-one-vertical-tile kind of cup that maximises the glaze coverage on the test tile. I know that some here have gone the opposite direction by mixing the smallest possible corner batches so as not to waste raw glaze materials.... but I am probably headed the other way, as it is enough work and time to do a Currie grid that I am not worrying about wasting a few bucks on materials. Anyway, still thinking about this. One thing I HAVE done with some of the leftover corner batches and cups so as not to waste them is to remix subgroups of cups and corners to make a smallish batch of a whole new glaze which approximates the chemistry of one of the cells. This has worked to some degree. If you mean on vertical tiles I agree. I think the biggest value of the 100% flux cell is when it is on a flat Currie tile for comparison purposes. That 100% cell gives a clear idea of what the glaze looks like with NO added alumina and NO added silica, so we can get a sense of how the glaze changes when we start adding those materials (which make up the majority of most glazes). More generally, I would say this is true of a number of the extreme or peripheral cells on a Currie tile. They are not so much “glazes” as they are visual points of comparison - and thereby information- on the cells in the interior space that we are probably more interested in as viable candidates. I am (trying) not (to be) a purist on Currie’s method. I know we have collectively made improvements to it already and I agree with you that there is more to be done. Yes! We have to keep pushing it, testing it, rethinking it - and ultimately making it better.
  15. NCECA

    will there be a coffee hour for CAD people sometime during the conference? and by CAD people I mean all of us here on the forums who are interacting almost daily for the other 50 weeks of the year. Might be interesting to run a poll (can we do that on these forums I forget) to see how many people on these forums will be there to see if it is worth it...
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