davidh4976
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Posts posted by davidh4976
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3 hours ago, Min said:
... and also pass the ASTM 325F oven to water test.
Maybe you mean ASTM 554? It calls for three passes of going from 250F to room temperature water without crazing. Repeat at +25F increments up to 450F. Crazing fails the test. Too much work for me! I just rely on three passes of boiling water to ice water to determine whether it's going to craze or not. It is a little bit more of a cheat for me because boiling water at my altitude is only 199F. Although the microwave test calls for doing ASTM 554 first, to me, the two tests seem mostly independent. If you are going to determine whether a piece is microwave safe, microwaving it and seeing if it gets too hot seems to be enough for me.
- Min and Kelly in AK
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3 hours ago, neilestrick said:
In all cases, the unglazed areas were a lot hotter than the glazed areas. When I measured down the side of the piece, they were all cooler at the top than they were at the bottom, presumably because they all have unglazed bottoms.
I also saw this on other test pieces I have microwaved. I believe it was because water had absorbed through the foot of the cup and was present in the lower part of the cup but had not been drawn up into the upper parts of the cup. The water heats up pretty fast.
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I tried an experiment. I microwaved five unglazed items made with five different clay bodies along with a beaker of water. None of these have ever been exposed to water. Humidity exposure is minimal (kept inside and in New Mexico where it is a fairly dry weather). Readings using a laser thermometer after 1 minute in the microwave:
- Cashmere and Ochre 100F
- Marilyn's BOD and Chocolate 120F
- IronStone 210F
These are all cone 5/6 clay bodies by New Mexico Clay. I am guessing, based on their appearance, that Cashmere (a white porcelain/stoneware mix like B-mix) and Ochre (a light tan) have the lowest iron content. Marilyn's BOD (a red-brown stoneware) and Chocolate (Dark Hershey brown smooth clay, almost black) have a bit more, again based on appearance. Ironstone is advertised as having so much iron that a magnet will stick to it which I tested and it's true! Fortunately, it wasn't so much iron as to fry my microwave!
I did not do the presoak as prescribed by ASTM because I was more interested in the effects of the iron in the clay body. Even without the presoak, per ATSM C1607-06, the Ironstone would NOT be considered microwave safe. Maybe someday, I'll make mugs out of Ironstone and the others and then run the mug test complete with presoak.
- Kelly in AK and Hulk
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8 hours ago, Min said:
Is this the original you were using? I've also seen this with 1 rutile.
Yes, that's the Reitz Green we have used; with 2 rutile.
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I used Frit 3134 for the boron and modified the quantities of other ingredients to keep the chemistry as close as possible. Same batch of rutile. Here is my latest attempt.
69.4 Nepheline Syenite
14.1 Petalite
8.9 EPK
4.8 Whiting
2.4 Ferro Frit 3134
0.3 Dolomite
0.1 Lithium Carbonate
1.0 Bentonite
2.0 Rutile
1.0 Cobalt Carbonate
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9 hours ago, Min said:
Is it just the tiny bit of GB you are replacing?
Yes! And, you would think that would be easy! Even with test pieces side-by-side in the kiln (one with GB, one without), the conversions that I have tried are coming out more blue than green even with the exact same amount of cobalt carbonate and rutile.
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I've been making good progress converting our glazes that have Gerstley Borate, Custer Feldspar, etc. The one that is eluding me is Reitz Green. Anyone have a version that doesn't include the no-longer-available ingredients? (I've checked Glazy.org and only found one, but it has no photo. https://glazy.org/recipes/449)
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If your 35.7 amp calculation is correct, you need a 50 amp circuit. A 40 amp circuit is not big enough because circuit breakers don't like running at more than 80% of their rating. It may be fine for some time, but then can trip at the most inconvenient time. In the U.S., the National Electrical Code requires the circuit breaker for a kiln (classified as a "continuous load") be between 125% and 150% of the kiln's rating.
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You should check the electrical "code" requirements for your local jurisdiction. Here is what it is for the USA National Electrical Code:
The U.S. National Electrical Code requires the circuit breaker for a kiln be between 125% and 150% of the kiln's rating (in US code terms, a kiln is considered a 'continuous load' which may be a similar term used in your jurisdiction). You can have wires that are bigger than required, so if you ever think you are going to get a larger kiln, have the electrician install larger wires. The cost for larger wires, unless it is a really long run, is minimal. It is safer to have the kiln wired to a switched disconnect box instead of using an outlet and plug, but if you need to move your kiln to use it, then a plug and outlet is OK.
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In my opinion, gas is not much harder than electric. A nice thing about electric is that with today's digital controllers, you can start a firing and let the controller handle everything. With most gas kilns, you have to monitor the kiln yourself and do all the adjustments manually for the entire firing.
If you must have cone 10 or reduction, you need gas...end of discussion. But, cone 6 oxidation in a digitally controlled electric kiln is more convenient.
You can get different results in reduction than in oxidation, but they are not necessarily better one way or another. The difference is primarily aesthetics.
- HenryBurlingame and Hulk
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When you open it up to measure element resistance, you also want to note how they are connected. Some may be connected in series and some in parallel. With that configuration information and element resistance, you can calculate the total current draw and therefore determine the required circuit size. If you are not comfortable with figuring that out, an electrician or anyone with electrical engineering schooling should be able to help you. If you take good photos of the connections inside the box, we might be able to help, too!
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The photos are a bit low res. I can't tell the model number on the controller. If it is an IPCO Studio 3000, you can find a manual here: https://kiln.expert/images/manuals-pdf/IPCOStudio3000Manual.pdf
It looks like the controller was not original but was added on replacing a kiln sitter. The blue part of the box make me think it could be a Paragon kiln. Similar to the current Paragon TNF233 10 Sided kiln.
Is there anything on the the data plate at all?
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If you want to do cone 10, you really want a gas kiln. You can do cone 10 in some electric kilns, but it's hard on the elements and not a great long term approach.
You might take a look at a gas kiln conversion called TDI Downdraft Kiln Conversion. There is a book on Amazon on how to construct it and how to fire it. There is a friendly FB group that can handle questions. I have one and can do cone 10 in five hours. I run it using two 20 gallon propane tanks. The first link below is a website by the creator of the TDI. The book has good info that can be generally informative on burners and firing even if you decide to go with a different gas kiln.
http://www.sebastianmarkblog.com/2018/07/gas-kiln-conversion-downdraft.html
https://www.facebook.com/groups/4124895130900261/?ref=share&mibextid=NSMWBT
https://www.amazon.com/Downdraft-Kiln-Conversion-Boris-Robinson/dp/B084DH88GH
- HenryBurlingame and Min
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I figured out what was causing this, but wanted to allow for a lot of firings to make sure. It turns out that inside the digital controller that I added, the 'wire-end' of the compression terminal on one of the internal wires was a bit too close to the controller's metal housing. I disassembled the controller (which was bought in one preassembled piece), and found signs of arcing. I put a good bend into the terminal, put everything back together, and have had no problems now over many, many firings.
- Roberta12, neilestrick and Hulk
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I've had to reformulate over half of our pottery glazes, both cone 6 and cone 10 to accommodate the end of Gerstley Borate, Custer, and Texas Talc. Using frits for GB, Mahavir Potash Feldspar for Custer, and dolomite/whiting for talc. Of course, all of the recipes needed changes to amounts of silica, kaolin, etc.
The tough ones seem to be the recipes that were "breaking" glazes or used some sort of lithium. Those took some tweaking and testing to get to a similar match to the old glazes.
Our local supplier has switched from Custer to G-200EU in their clay body mixes without any noticeable difference.
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Does the mesh level of dolomite make any difference in glazes? Pottery suppliers seem to offer both 200 and 325 mesh, but I've never heard of a difference for using either one.
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Everyone' comments have convinced me that a100 pound tank for all three is unlikely to work.
We are going to go with an individual 20 pound tank for each kiln with the tank placed in a tub of water warmed by an aquarium heater. In the past, we have run a good number of raku firings with 20 pound tanks and no heaters and we only had one freeze up on a day when the ambient temperature was in the low 40s.
I successfully use an aquarium heater on a small downdraft kiln that I fire on a pair of 20 gallon tanks for 5-to-6 hours to get to cone 10. The heater does a good job of keeping the water in the tub in the 70s.
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Is the glaze coming off during the firing and landing on the kiln shelf? If that is the case, it can be due to the way the wet glaze dries and cracks and falls off.
If the glaze is not falling off onto the shelves, but is leaving bare spots, that can be a different cause.
I can't tell which is happening from the description or photos.
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3 hours ago, PeterH said:
Just for the record Ceramic Arts Daily publish "15 tried and true glaze recipes" for (at least) raku, cone 6 & cone 10.
Ah! I missed that there are three different versions of their "15" recipes! All of the raku recipes have less than 20% clay, so extra clay is probably not the problem.
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I think the "Ceramic Arts Daily publication of 15 tried and true glaze recipes" are all cone 6 recipes and would not be well suited for Raku. I don't know about the Gary Ferguson recipes. Can you share your recipes here and we can take a look at them? Since the flaking is happening with both dipped and brushed, it makes me suspect the amount of clay in the recipe. With too much clay, the glaze can shrink during drying, crack, and flake off before firing.
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22 hours ago, neilestrick said:
I think you'll just have to try it. My gut says 3 kiln is too many, though, and you'll get freezing.
My gut also says that freezing is possible. Since no one is confidently saying that it's no prob running three raku kilns off one 100# tank, I think I will abandon the idea of using a single 100# tank. I would hate to invest in the 100# tank, regulator, and plumbing and then find out it freezes up!
Our alternative is to continue using the 20# tanks; one for each kiln, but we will put the tanks in tubs of water with an aquarium water heater in each. I think this will work because we have only had the freeze ups in colder weather.
I do aquarium heaters with my personal gas kiln and I have never had freeze up. My configuration on my personal gas kiln is a TDI downdraft converted Skutt 1027 using two 20# tanks ganged together. Both tanks sit in a tub with an aquarium heater. I start at 0.5psi and run up to 3psi on a single Ward MR750 to get to cone 10 in 5 hours using less than 4 gallons of propane. No freeze ups.
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14 hours ago, Bill Kielb said:
Do you know for sure how many btu your present burners are rated? If not you can sneak up on it with how many firings in a 20# new cylinder. Conservatively you will likely get down to 1/3 - 1/4 of full charge before it becomes difficult to use, especially at 40 degrees. There are about 4.6 gallons (440 kbtu) in a 20# tank so basically 5 times more in your 100# tank.
They are Ward MR750 burners. We run them starting at 1 psi, going up to 5 or 6 psi. Ward says the MR750 is rated at 54,365 BTU at 1psi and up to 153,768 BTU at 8psi. That matches our fuel usage that we measure by weighing the tanks and confirming with the amount of fuel put in each tank when it is refilled.
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6 hours ago, neilestrick said:
I think you'll just have to try it. My gut says 3 kiln is too many, though, and you'll get freezing.
How is your kiln constructed? 40 minutes to an hour seems a little long for a typical raku kiln.
We have a few different kinds. One is a 55 gallon drum lined with ceramic fiber; about 4 cu Ft. We are moving to only having this style. We are experimenting with ramp-up times will probably up faster in the future.
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Because we are doing raku, we run the MR750 burners at higher pressure. Starting at 1 psi and going up to 5 or 6 psi. (From Ward regarding raku: "With 1-8 PSI, the MR750 Single System is rated at 54,365 to 153,768 BTU's".) The firings last from about an hour to about 40 minutes each depending on if it is the first firing or subsequent firings. I'm guessing we are averaging about 100,000 BTU per kiln per firing which tracks about right with our fuel usage. If we do three firings on each of three kilns, that should be about 10 gallons so a 100 pound tank has enough fuel.
My bigger concern is tank freezing. My understanding is that using a 2 stage regulator system will help prevent freezing. I also think I understand that the tendency for a tank to freeze is related to the surface area of the liquid in the tank. A 100 pound tank has about 50% more liquid surface area than a 25 pound tank. What I don't know is how all of this translates to real world experience! (We've had a 25 pound tank with single stage regulator freeze up in 40F weather, but the tank on the next kiln over did not freeze up.)
I'm seeing 1st stage regulators that handle from 1,500,000 to 2,250,000 BTU/hour depending on the model all at 10psi. They are all in the same price range, so I assume that the higher the BTU/hour, the better. So, my conceptual configuration is shaping up as: I'd use a 100 pound tank with a 1st stage regulator reducing the pressure to 10psi, then a manifold with individual valves for each kiln, with hoses leading to adjustable regulators (0-to-30psi) near each kiln, followed by the MR750 burners. I have to figure out my hose lengths and therefore sizes.
wedge not sticking to MDF insert
in Studio Operations and Making Work
Posted
After you slam it down, don't go directly into an upward coning. Instead start with a forceful pressing down into the hockey puck shape. Then proceed with coning. This helps with adhesion.