Bill Kielb

If I understand this, you programmed for 108/hr and actual firing it achieved 120/hr. Further you programmed 350/hr and it actually achieved 344/hr. My initial thought is it was operating at the Precision it could. In the 108/hr segment (more overshoot in the algorithm) and in the 350/hr segment maybe a combination of what it could achieve power wise and undershoot in that segment. So my initial thought is many times programs do not fire perfectly at the rate programmed. Quite often when rates are programmed that exceed the actual power available they really go a lesser rate. How well a controller matches temperature throughout the firing is dependent on several programmed characteristics in the controller. One would be relay cycle time. My experience, kiln controllers do a pretty nice job of matching the kiln characteristics so those actuals would not alarm me. It would tell me though for that loading, you don’t quite have enough power to maintain 350/hr, very close though and you have enough power to maintain 108 degrees per hour in the final segment. The final segment to me is most important as that is where you are providing significant heatwork to match the Orton columns of maturity. Orton says this starts 200 -250 f from the desire peak temperature (in the Orton chart) The ten minute hold, Ireally can’t speak to, maybe you were trying to drive this 1/2 cone higher. People have all kinds of schedules that work for them, often very different and much more complex than just following the instructions In the Orton chart. The big question to me is did it fire to the cone you were seeking?

It sounds like your power source is not able to supply all elements in parallel. A 2400 watt element with 240v across it draws 10 amps. 20 of these in parallel would be 200 amps. That would be 48000 watts of heating energy. Very large home kilns are approx 12000 watts of energy. Each element right now should be 24 ohms as you have designed. So my sense is when you connect several of these in parallel whatever power supply you are using has a severe voltage drop and they do not heat up as expected. I would combine these in series parallel to get down to 12000 watts which means an overall resistance of about 5 ohms. Unless you have built the biggest kiln ever, 48000 watts is too much. At 12000 watts your power supply will need to be capable of supplying 240 v @ about 48 amps without significant voltage drop.

Don’t fire on drywall it will smolder and burn once calcined. Used to be type X 5/8” - approx. 60 minutes, 120 minutes to sustain a flame. I like the shelf idea and unless once firing, you can grog / silica the shelf after bisque. Many of our large format sculptors would build on a very straight shelf on top of a four wheeled cart.

I do not have a preferred store purchased overglaze. I spent a whole summer trying to resolve this for our cone 6 glazes so our artists could paint freely with most underglazes. The solution was to modify a clear with a bit more boron to more completely melt. If this is your issue then testing other commercial. over glazes as well as lighter coats of underglaze are probably your best bet. I have never noticed a difference between clays but only anecdotally tested on the variety of studio clays used at the time. Color, thickness applied and even underglaze supplier had the greatest effect - all reasonably resolved with a slightly lower melting temperature of the modified clear. Not all under glazes will go to cone 10 as well with significant color change often being the effect of higher temperature. All our artists, especially sculpture test their underglazed for color. It was not uncommon for a sculpture artist to say, I need to stop at cone 2 - no higher as the perfect color of a full sized human bust that took them a month to make might change from what they wanted. A bit tedious, but an example of all tested in advance.

In the UK the declared mains voltage has been 230v single phase I believe. North America uses 240v but split between 2 phases ends up at two 120v circuits to neutral. I think it would be odd to have 120v available without your very own step down transformer. Check before buying for sure to be safe. Check a light bulb or two - ought to be rated at 230v in the UK.

Pictures for sure for ideas. One experience - Not all clear glazes melt well over underglazes so the underglazed decorated area can be locally refractory. The end result for this defect, bumps, orange peel, glaze that does not cover and melt well to a smooth finish. Often mistaken as over fired and bubbling. Additionally if heavily underglazed, when applying glaze over the top the underglazed area is far less absorbent than naked bisque so it can be hard to apply glaze over the top evenly. Spray applying overglaze and drying is one way to get a pretty even coat over the entire ware. Pictures for sure here as there can be other reasons for sure. Most underglazes need to be tested with their overglazes in the manner they will be used to be reasonably sure the combination works as intended.

Hard to know the formulas for sure of commercial glazes but there are many sources for glaze recipes. Glazy.org is one web resource. Making glazes for many potters is a thing though, often to save on the high cost of commercial glazes but also often to design glazes that are very durable, to their coloring and finish preferences. You can browse glazy (and others) for something that might be similar.

Whatever you do, I urge testing. Many of these things folks mentioned above can cause significant acute effects in super small quantities. So small you can’t smell them, but may have acute effects on peoples ability to smell, mood swings, etc..…..you have symptoms, you really want to know the origin of the symptoms. It may have nothing to do with how things smell to folks not affected or how the contaminant smells in strong concentrations. One of the items mentioned above, Perchloroethelene (dry cleaning fluid) has varied effects on humans in doses too small to smell. Your symptoms appear severe, it seems like real tests are important for discovery. If discovered and if you are seeing a doctor, they can often do tests of the concentration in your blood. That is often how these things are discovered. My thought: Please get some testing, please see your doctor. You will never ever be able to smell parts per million or parts per billion of perchloroethelene. Hopefully it is something simple - best way I believe to understand though is testing.

Copper is interesting and there are limits but most often found in an industrial setting when testing for heavy metals.. Sounds like you need a real environmental air test and lab analysis to figure this out ……… then figure out the source. Clay may or may not be a concern here so a real test with real quantities of constituents likely is the best way to know with reasonable certainty. For now, no exposure or very limited exposure until you can correct seems important. Adding cleaning chemicals, moisture etc… can amplify effects. I suggest get a real test and lab analysis ……. on paper by an industrial hygienist or equivalent.

The 2280 on the side of the kiln likely means it is rated cone 8. Folks who fire to cone 6 generally buy a cone 10 rated kiln. The higher rating simply gets them more firings on a set of elements than a lesser rated kiln. Your kiln with new elements ought to get you cone 6 firings, not as many as cone 10 rated but a fair amount. You have a manual kiln, great for learning! If you search the web you likely will find helpful information on manual kilns. Here is a YouTube video I spotted for firing a manual Evenheat kiln. https://youtu.be/AFI5zYdRJ8E?feature=shared

Looks good - do you fire or just learning to? What cone do you fire or hope to? The Evenheat manual Is probably available online, might be a good place to start. Study a bit before firing …….. stay safe.

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.