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curt

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  1. curt

    Most used sieve size?

    80 mesh is good because most anything that passes it will also go through a sprayer without blocking it up.
  2. You might even search these very forums for the word “oilspot”.
  3. Note: OK, struggled for quite a while to get this photo to upload, first time doing it with new software update. Tried to upload to my gallery several times with different file sizes but no joy. Every time I hit "submit photos" button after uploading, nothing happened (ever). If anyone can point me to instructions would appreciate it. As promised from tiles above back in mid-March, this is the same glaze as above, but in oxidation (electric), and probably fired to around cone 9 (cant say for sure because I did not fire it.) Most distinctive feature is still the stark divide between not so much zircon (2 left columns) and too much zircon (3 right columns). Other than that, this glaze in oxidation appears to be behaving very similar to reduction, with the obvious difference that the light iron content here is making the glaze brown, rather than green as it did in reduction (see tiles above). The bottom 4 cells of the middle column are probably the most interesting to me after looking at this for a while. I am tempted to do another tile that zooms in on this area to see what is really happening when the zircon/silica is changed in much smaller increments. At some point between columns 2 and 3, the zircon is going to appear on the scene. I know zircon is very refractory, but I can't tell (even after looking with 800x zoom microscope) if the zircon is just sitting in this glaze doing nothing but looking white, or if it is getting moved around, dissolved, or otherwise homogenized into the melt. Obviously small amounts simply vanish, as we can see from the two left-most columns. The original glaze is around corner D, basically matt white. I am waiting on one more refire of the reduction tiles above and then I will post them again, maybe with a bit of compare and contrast if I can manage to organize the photos.
  4. curt

    How hot does this kiln get?

    Whoops sorry Joel you are right. 1300 going to be very hard (impossible?) with this kiln. I was thinking about my own experience with a 240 volt (not 110 volt) 15 amp kiln when I said that. Which had no problem to get to 1300 C with newish elements (struggled when elements got older though). I have a 240v 10 amp test kiln (about 1 cubic foot) that also has no problem to get to 1300, although the (small gauge) elements clearly do not like this treatment,
  5. curt

    How hot does this kiln get?

    I can see the pictures. Looks solidly built. 1600 Kw kiln could get you to 1300 C in principle, depending on sufficient power supply and the condition of the elements, which are not visible.
  6. curt

    Beach sand instead of grog?

    Yes have used wild sand. The main contaminant was iron and calcium chunks for me. It is easy to add too much, makes your clay body non-plastic and prone to crumbling rather than stretching. Take care to get a particle size distribution which mimics the grog you would have used. Wouldn’t worry about the salt. Will be almost irrelevant in the scheme of things. Beach sand is OK but isn’t it very coarse?
  7. Nice work, LT. Jafa, since the highly textured surface is in fact the main decorative element, you don’t want any other surface treatment that gets in the way of this. To me, that means either a) something very dry and thin as suggested above, applied all over, possibly changing the colour and tone, which removes any visually distracting glare and shininess, thereby leaving the surface texture very proud very visible. Do not use distracting colours or layers since these detract from the richness of the surface texture which is what you want people to see. Or b) a breaking glaze that accentuates and highlights even the tiniest bump, adding zing (!) Or, c) some process, eg wood firing, that accentuates the unevenness by colouring up the high points while leaving the valleys bare, creating strong contrast between high and low, or d) hand applied stains or washes that are put on and then rubbed back to create contrast by making high points bare clay while leaving colour in the valleys.
  8. Sea slugs. Easy to catch and very cuddly....
  9. curt

    Outdoor firing

    Outstanding. Kind of reminds me of the guy who hiked the Inca Trail to Machu Picchu armed only with a sheet of plastic and a can of beans. I had thought of the culvert being upright but I can imagine the train kiln set up. So are you saying the culvert wasn’t lined inside with anything at all!? That is, you were firing a concrete culvert to cone 8 or 9?
  10. I pug clay. There is no pressure. Nothing that must be done. No finish line. No phones, no computers, no TV. No control. The pug mill tells me how fast to go, gently ignoring any pleas to go faster... Just lovely plastic handfuls of clay, Iike the first time you touched it. In. Out. In. Out. In. Out. The mineral earth smell, cold and damp, squeezing through my fingers. Slap into the hopper. Down comes the plunger, extra force applied right to the bottom to leave no doubt about who is really in charge of everything in this little world. Endless, rhythmic repetition (cut, smash, cut smash, cut smash), the low steady drone of the motor, the slow but inevitable extrusion of perfect worms, again, and again. ... hypnotic....like a wheel going round...and round.... ...the mind wanders, ... sequences of thoughts lead strangely down side paths. Ideas occur, new but vaguely familiar, coming from somewhere like things that happen in a dream. Forms appear in your minds eye, once known, then forgotten and now rediscovered... have hours passed or only minutes? No idea. Cut slap smash. It goes on. You are far away now. a distant call to dinner shakes you awake.. back to earth. switch off the pugmill. As the dream fades you quickly you scribble down a few thoughts, rough out a shape or two... tomorrow is another day. As you drift off you know fresh pugs of clay wait silently in a neat stack, filled with possibility, daring you to try something new...
  11. curt

    Outdoor firing

    LT do you have any pictures of this concrete culvert “kiln”? I am assuming the firebricks were on the inside? How did the concrete (with reinforcing or without?) hold up after a number of firings? I have a few big culverts (42.5” interior diameter, 25” tall) sitting around which may have found a new purpose...
  12. curt

    What are the pitfalls?

    Use a needle tool to check the bottom thickness when you think you are getting close. Poke straight down until you feel the wheel head. Eventually, as others have said, you will naturally get pretty close. However, I find that since I throw all sorts of shapes with all different amounts of clay all the time, I still often check.
  13. However, understand that “dry” doesn’t necessarily mean leaving a pot just sitting out on a shelf somewhere. If you live in a climate that cycles through wet and dry seasons, and cold and hot temperatures extremes, humidity levels in the air can also move up and down substantially over time. This affects things made out of clay which have not yet been fired. Dry pots absorb and desorb lots of water from humidity in the air, through the small channels in and around clay particles. Unfired clay effectively inhales and exhales humidity over time. Think of it a bit like a rigid sponge. This matters because clay shrinks and swells as it’s water content changes. While most of the shrinking happens in the day or two after we take a pot off the wheel, shrinking and swelling stresses are still at work in a small but meaningful way even when we think of the pot as “dry”. And different temperatures also promote water movement, in the pot as a whole, and also in different parts of the same pot. Humidity fluctuations may or may not matter, depending on your clay body and what is in it. Big, gutsy clay bodies which are relatively “open” ie a good range of large and small particles sizes with grog, silica sand or other aggregate strengtheners, along with sufficient colloidal material may have very good “dry” strength. Fine porcelain bodies have larger smaller particles, greater surface area, and smaller pore channels, but little in the way of aggregates to strengthen the body, and can be more fragile. Different clay body ingredients can also impact how well a clay body withstands humidity cycling. Sodium Bentonite, for instance, which shrinks and swells dramatically, is a common clay body plasticiser, and small colloidal particles like this are actually the main source of green strength in dry pots. It is mostly not a a problem since our clay bodies have so little of it, but should not be forgotten, as some bodies lean on bentonite more heavily. Ball clay shrinks and swells less than bentonite, but there is usually a lot more of it than bentonite in clay bodies we use. Point of all of this is that pots can be negatively impacted by humidity cycling, and to a lesser extent temperature cycling, causing weakness, cracks which show up later during glaze firing, and in extreme circumstances even dry pots disintegrating where they sit. The longer you leave them exposed, the greater the risk. The extreme version of all this would be if your studio is in a rainforest, and you leave a pot on top of the kiln you fire every couple of weeks, and which is also exposed to the sun on one side. That should be the perfect storm. Moral of the story is if you want your dry pots to last and fire OK later, try to avoid putting them through conditions like this.
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