davidh4976

I've pulled my copy off the shelf and read the entries for each oxide and flux in general. It only makes me again realize how complicated some of this can be! Thanks for pointing in that direction.

Great discussion! Is there any published information that compares the effectiveness of the fluxes? For instance, in adjusting the melt of a glaze, in fluxing power, is there data that says BaO equals x times K2O? Or something like that?

Interesting... in John Britt's video, he says 2-to-4% Bentonite.

4-to-14% EPK depending on the recipe. I have not yet used Epsom salts because I am following John Britt's guidance to use up to 4% bentonite before using Epsom salts, and I am able to get rid of the hard panning without exceeding 4% bentonite. I don't really know enough about the trade offs between Epsom salts and bentonite, so I have to rely on people who seem to know what they are talking about!

We just inherited an Olympic 2831G gas kiln. We are thinking about using it to fire to cone 6 reduction. Anyone have any idea how long a typical cone 6 reduction firing would take?

Because of the availability issues for Gerstley Borate and Custer Feldspar, I've been converting our studio glazes to use frits and G-200/Mahavir feldspars (with some tweaks for other ingredients to get the chemistry right). One thing that is quite noticeable is that many of the new versions will hard pan without the addition of Bentonite to the recipe. Some need as much as 3 or 4% Bentonite. I'm doing line blends with different percentages of Bentonite in order to find the minimum amount that will prevent hard panning and keep everything in suspension for a reasonable amount of time. I'm just offering this as an observation for anyone who is heading down this path. I'm 90% done with our recipes that need conversion. Later, after I get all the recipes completely done, I may experiment with other versions of recipes to get to the same results without needing Bentonite.

I'm using a barrel lined with 2 inches of ceramic fiber with an MR-750 venturi burner. Sometimes, the kiln stalls around 1650F. Other times, I can get to 1850F with no problem. During the latest firing day, the first firing went to 1850F with no problem, but the second firing stalled at 1650F. I grabbed a weed burner on another tank and put it alongside the MR-750 and was able to easily bump it up to 1850F. After the second firing, I experimented with the dual burners and was able to easily get to 1950F. But, it's puzzling why I can sometimes get to 1850F with the MR-750, but then immediately afterwards try another firing and have difficulty getting past 1650F on the single MR-750. I'm thinking the port/flue size might be the issues (but, welcome any other thoughts!). Any thoughts on how big the burner port and flue should be when firing at 7,000 feet elevation? Any other thoughts or tips?

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.

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.

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.

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.

Yes, that's the Reitz Green we have used; with 2 rutile.

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

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.

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)

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.

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.

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.

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!

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?

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

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.

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.

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.

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.