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Bob Coyle

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About Bob Coyle

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  • Location
    Santa Fe
  • Interests
    Metal work and electronics

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  1. Usually pit fired pottery is not glazed. Different colors are made by use of metal salts sprayed or dusted on the pot as it is put in the pit. There are lots of you-tube stuff on pit firing. It is tricky for a new comer. Many people bisque their pots before a pit fire. That way there is less chance of blowing them up.
  2. My guess is that the clay has fines that are slowly forming weak hydrogen bonds and pulling the particles closer together causing shrinkage. This is just a guess though. Take three pans and mix a little vinegar to one and a little magnesium sulfate to the other. In the third one just use the fine clay. You should see a difference. Are you going to use this as a slip?
  3. I make 1 inch by 1/4 inch clay "coins" and put some of them under all of my pieces in the kiln. This allows heat circulation under the bottom and keeps it 1/4 inch above the shelf. Never get any sticking. PS... You still need kiln wash on the shelves for the pot that drips.
  4. Bury them deep in your back yard... in 1K years some archeologist will go crazy over his or her find!!!
  5. When I logged in, I saw only one reply to your post. The reason is that Chris pretty much gave a complete answer. Glaze "fit" problems are a reality for all of us who work with clay. You need to follow Chris's advice and work through the problem. PS If you are new to clay, your piece looks pretty nice. If you get a little crackle in the glaze of a non-functional object, just think of it as a "feature". and work from there. The whole ceramics form of Raku rises or falls based on the intentional crackle pattern of the glaze.
  6. I'm not to worried about the squirrels... The neighbors bird bath was knocked over by a bear. Thanks for all the good advice. I'll have another go at it and try out some of the suggestions.
  7. So I thought I would make ceramic bird baths for some of my outdoor sculptures... It's just a big plate...what could go wrong?? Well first off, I decided to just go with an 18 inch slab with upturned rims. I dried it too fast and the lovely upturned rim detached itself from the body. So maybe I was stressing the clay around the rim by just bending it up by hand and paddling it on the outside. So I rolled out another slab and brought it to almost leather hard with a heat gun and slapped it down on an 18 inch bat on my wheel. I spun the edge up as I normally would for a plate, and worked the bottom of the container with a rib to try to minimize s cracks. Well the bird baths are now drying ...slowly... but I noticed that the center has a slight upward bulge. I sprayed it with water to soften it and pushed it back down, but as soon as it got dryer, the bulge was back. The good news is that the rim is holding on this time. Lord knows what will happen when I fire it. So any of you large platter makers...What am I doing wrong and How do you do it right?
  8. The proximity of your hand to the belt drive in the vid, looks like an accident waiting to happen. Maybe you should move over to the other side to dump the rocks in.
  9. Sounds pretty strange that an element would have cold areas. The same current will be flowing through the entire element. I have had places where the element was thin, and glowed hotter than the rest of the coil, Maybe that is what you are seeing. It is usually isolated to a small section. The only way you can know if the element is not pulling enough current is measuring resistance of both elements. If one is way high, then there is a problem. Another place to look is the relay in the controller. If it is getting overly hot during the run, the amount of current it can pass goes down. This happened to me once in a setup I did where the fan cooling the relay was not strong enough. If it is a solid state relay,and getting up to temperatures greater than about 170F then you may see a drop off as the kiln heats up. Can't think of anything else... measure the resistance, otherwise we all are just guessing.
  10. A six meter cord, if it is not the correct wire diameter, May give you a voltage drop that will cause the kiln to not get as much current to drive the elements. If the cord gets hot to the touch when you are firing, then it may be a problem. If you are running 15 amp wire for a 13 amp kiln, then 6 meters is pushing it. Ohms law i= e/r amps = line voltage/ element resistance. measure the total resistance of the kiln by unplugging it and turning on all elements to high. measure directly across the plug at the kiln if the line voltage divided by the measured resistance doesn't give you pretty close to 13 amps then you have a problem. Try the same same thing with it plugged into the long line. Measure at the end of the line and see if you get a difference. If you don't know what I am talking about...don't even try it.
  11. A very good start for dip and pour, but I do short glaze runs and only make enough to brush on... a whole new ball game. If I would give advice on brushing, the main thing I would say is keep the glaze thick, and try to "flow" it off the brush rather than painting it on like you would do a wall in the house. That way you do not have to do it twice, and You don't get streaks. The key to a "flow" is to load up the brush and stop brushing when you feel it begin to starve out and pull against the clay. Load up again immediately and try to keep a "wet edge" (as the house painters say) against the last brush stroke. Thick glaze minimizes streaking since the glaze tend to level over the surface as it fluxes and becomes fluid. PS ... dip and Pour are the way to go if you are doing production runs.
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