Bill Kielb

Unfortunately I am not a reglazer. I find for cone 6 and 10 it stresses my wares a bunch and really I have very limited success. For low fire stuff, this may be very different though. Occasionally I will lowfire a cone 6 piece to change the look or add accent. I think you want to fire to whatever the glaze matures at or has been fired to and performs best at.

I would only add the suggestion that all ought to be effectively protected by a gfi. Tank heaters without the third prong (ground) cannot really be effectively protected. Same for all devices without the third prong. Water, electricity, possibly lots of folks nearby, firing kilns, red hot wares - best to be as safe as practical.

It all really comes down to energy draw and the ambient temps. Charts can help and knowing your actual energy used really helpful

This may help, most things expand and contract with temperature. How fast and therefore how much they do that, becomes one of their finished properties. Glazes that craze generally grow slower than the clay they are applied to or the clay is growing faster than the glaze does. In effect a fit mismatch hence Min’s clothing example. We really don’t know these rates for clay and glaze until fired to their final form. So testing the clay and glaze combination is often the only way to know they reasonably match. It’s been said that getting a perfect match is extremely unlikely and some day the glaze will craze. Maybe 100-200 years from now - delayed crazing. So crazing or glaze fit is not necessarily a function of cooling something quickly but ………… large temperature swings can help reveal this mismatch. Folks often test from boiling to freezing to try and see how well they fit. So very large swings, much more than your 40 f temperature are often used to see if the delay is on the horizon or as a way to validate a decent fit. Simply testing the combination together is generally the only way to know they fit. In theory high differential testing reinforces that they fit well.

I would agree with all above, including the sheer size of the blower motor on top. This seems very industrial for a simple kiln and my guess is you would need to scrap a lot of what they are doing here to likely be used with atmospheric burners. Just curious if you have power available as well, might be three phase by default.

Since the elements glow, the relay is not likely the culprit. Measure the resistance of your elements and if they have risen by 10% then they need to be replaced. Since Fth occurred at such a low temperature, it’s fairly unlikely to make it to much higher temperatures in an acceptable time frame. If you get high measurements then you can be reasonably confident that is the issue and choose to replace or inform the buyer that it needs element replacement.

I would call Orton - the only F prefix errors I see are on page 13. Assuming this is your manual https://www.ortonceramic.com/autofire-express-products

Yep! It will likely tighten somewhat so a nice 10 hr bisque to 05 / 06 might be just the thing. Time at temperature is important to complete burnout. You might be able to work out a slower turn up schedule so it’s not such a guess each time. So turn up to ten, then maybe 1-2 hours nine / eight …… a cheap pyrometer can help a bunch here. Anyway, a way to slow things down and for bisque a way to try and burn everything out that could cause problems by going slowly. All part of testing and learning kiln, clay, glaze…..

Crazing is a clay and glaze expansion mismatch issue. In general it’s usually related to the match between clay and glaze and probably rarely related to bisque temperatures so I don’t want to confuse two issues here. As far as pinholes, yes effective bisque may help with pinholes. If all the organics are not burned out in the bisque, they can create a pinhole issue as they burnout in the glaze firing. Effective burnout of organics depends upon time AND time at temperature. Most bisque cycles run 10-12 hours to try and ensure all organics are removed. So now I think you know that you can fire slower and when you have reason, modify your turn up schedule as appropriate. Originally I think you felt that it was firing as slow as possible ……. Hopefully now you have a way to go as slow as you find necessary, bisque and glaze.

FTL message usually indicates not enough power to get to temp. Worn element(s), bad relay - some mechanical or electrical reason it cannot maintain a reasonable rate of heating at the end. On the test tile side, Orton says most of the important (flux) heat work work will be done in the last 200-250f degrees given a reasonable rate of rise during this period. If your kiln stops well short of that last 200-250 degrees then generally things can be restarted as if nothing significant happened. In your case, you are sort of close so restarting likely fine if you can make temp at a reasonable rate. If it stalls again though you are going to need to diagnose the problem and those tiles are likely half baked and depending on the stall temp can end up looking any number of ways. If you have witness cones in place then plus one - you will have an idea of how much heatwork you achieved. If virtually none, then repair the kiln and refine. My guess is it stalled for a reason and It will stall again. My rule of thumb is if it stops 250f or more before it’s final temp it usually can be cooled and refired after repairs with it likely ending up looking / firing as normal. In effect no heatwork was done during the most important phase.

How about an empty firing to 04 just to see how long it takes to get there with the dial set at 10 and never turning up? Maybe make sure you can make it in ten to twelve hours? It’s just getting to know how your kiln fires so you can apply it as needed.

Maybe time to test it out?

If you leave it on 10 with your normal peep hole procedure, how long does it take to get to 03, or 04?

While Fast glazing may / may not be a problem, fast bisque generally not the greatest practice unless you know your clay has burned everything out in that timeframe. To slow things down modify your turn up schedule leave it on low for longer or turn it up less. Duncan provides calibration instructions for the switch. It may be too old to calibrate but following the analysis part should reveal if it is just too worn and needs to be replaced. For now, just as a test, I would slow down the bisque simply by firing slower, more in the 8-12 hour range for sure to see the effect on your clay and glaze. If you leave it at the 10:00 position and do not turn it up, how long to 04? If that extends the firing, then calibrated or not calibrated you have an option to slow things down to test with.

What is your firing schedule?

One thing comes to mind as possible and non destructive (so to speak) for extremely difficult bolts, etc we used to use an impact driver. Back in the day this was a very manual thing you pound with a hammer. Today cordless drill and driver sets are very common. If a hex key still fits, you could get an impact driver hex key and likely remove it with that. Amazon, harbor freight have some real cheap impact hex keys that fit todays drill / driver and you only need it to last for a couple removals. So if you have an impact driver or can borrow a friends and the hex key still fits, this may be a very good option. If the hex key no longer fits, they make impact driver extractors as well. If you drill this thing then only drill the center to fit your extractor and not to over-drill and damage the threads. Drilling this completely out probably creates the most work to restoring with a larger set screw and newly threaded hole. Last piece, lots of study about penetrating oil, many favorites, rarely do they work on their own though. Most still require significant mechanical energy to get the thing moving so don’t get too discouraged. The impact driver just might give you enough mechanical advantage to free this up relatively easily.

Do they extend out of the hole or are they fully embedded? Maybe post a picture.

Lots of boron in those recipes Min linked. They look low fire / raku.. tried fergusona white, and two of the copper. Results were fine as I recall.

Presumably driven by cost, ease of use and not wanting to slug water around in the cold, locally I see self regulating heat tape for cold weather firings or a big box power blanket bucket heater.

Just perhaps an easy thing to remember - Flat plates with a hole in them start off with a pretty distinctive stress concentration. Have seen many a clock face crack just like in the pictures above. Reinforcing around a hole can help with clay, just like many other materials, this pattern and fix are similar to help many materials survive this typical stress concentration around a hole - pictured below. We reinforce all holes in flat plates with some added uniform thickness or washer if you will. Since, along with good practices no longitudinal cracks in these clock face figures.

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.

Yes it will Yes I do, but it is complex so testing may have helped here. My guess is it would help. Total guess though. Pres used grog, I think I said silica, alumina is great too. Pres had the super excellent idea of applying thin and evenly with a salt shaker though. All can work, all require care not to spread around the kiln. Grog is probably neatest, then silica, then alumina.

Interesting, so the MR70’s you are using will have medium pressure orifices. A larger 1st stage regulator will not respond as well as a smaller so probably not necessary to go to the 2.25 mil. Ten psi hose from the tank easily supplies 300 k - 500k btu and a single second stage from 10 psi down to your working pressure also easy at 300-500k btu. (Larger here is definitely not as accurate as one that matches the load best). So if the kilns are on a common manifold near each other it sounds like one low pressure regulator can feed all three and just use a hand valve and pressure gauge to fire each. Frost is complicated so as your tank empties it also has less thermal mass and tends to frost quicker. Trial and error here is almost a must. As to the primary regulator freezing, likely not much of a concern.

One thing that comes to my mind for large pieces, is it will shrink and grab on the shelf. The rim and likely the grid if flush at the bottom will tend to drag on the kiln shelf. The grid itself if not reasonably even could also cause this to warp and bend depending on variance in thickness and construction. A waster slab and thin even silica beneath and between comes to mind to keep it smoothly moving and from grabbing. Same for glaze firing, although predicting distortion I think is tough without having tested a few shapes and if glazing only one side could deform the shape. Sounds like you can glaze both to a large extent. Quartz inversion (IMO) is almost not a thing as every piece in every firing goes through it twice each firing the world around (probably millions of pieces). Having said that a reasonable slow speed helps with the rate it shrinks and there is no reason to go to cone 04 so neither of those suggestions sounds silly. We do multiple bisques with layer applications of underglaze but always bisque to lesser temps just to set each layer of underglaze. There is no reason to waster the energy or stress the piece.

Most burners are rated in Btuh @ a specific pressure. If you are buying them from Ward then INCHES of pressure is what you need, not PSI. 1 PSI = 27.72 inches, ward burners are typically rated to 11” wc (propane) to get to peak output. Easier way to do this is figure how many btu you will use, know this number. Once known - convert to gallons for an idea of how long the tank lasts. Normal propane design, 1st stage regulator reduces tank pressure down to 10 psi. Second stage regulation goes from 10 psi down to 11” water column. At 90 degrees tank temp you are approaching 200 psi. Running 200 psi line not the safest idea so reducing it to 10 psi improves safety and still allows a whole bunch of btu for a small diameter hose. Best idea I have, sketch what you want to do and include realistic distances and btu required for all the legs. From there it’s pretty easy to pick stuff from a table if all that is known. Look at the ward burner spec below and decide if you are trying to follow that or run your burners at medium pressure. The first stage tank regulator will need to be sized by the load on it (total btuh) Proper sizing is important. A 100 pound propane tank contains about 23 gallons. One gallon of propane contains about 91,400 btu. The MR750 will consume approximately 77,400 bru per hour full blast at 11” of water column.