High Bridge Pottery

One of the reasons you are having difficulty with mold release is due to your print lines.  They add a texture that will cause the plaster to grip your 3D printed surface.  So any roughness needs to be filled in, sanded out, or smoothed over.  It doesn't mean that you can't have the texture but at least coat it with varnish or something to help smooth it out and fill in micro undercuts.  All those little places you have plaster sticking inside of the print lines are forming tiny undercuts.  The main problem with 3D printing, IMO, is that there is a TON of cleanup.    I 3D print resins of my horse sculptures and no matter how clean my prints, how much I fuss over no print lines, temperature and other issues still cause so many nit picky things that I can literally spend hours cleaning up a single print afterwards before it's usable for mold making.  
By the way, you can also 3D print originals or mold masters in rubber!  This is super nice for pouring plaster molds and works a lot better than using the hard plastic.  But again, you need super perfect printing because you won't be able to clean up rough areas in rubber as easily as you can with plastic resin.  So as the technology is still evolving and not nearly good enough unless you really, really know what you are doing and that's a steep learning curve.  I've been 3D printing two years now and there's still a ton I'm trying to fine tune.  So mostly I still use the old fashioned methods of pouring rubber and building mold boxes.
Pardon me - I see belatedly that others also pointed this out so I'll just agree with them!    (edited to add this comment)

I usually fire my kilns at night so I don't really see what's happening with actual temps in the kiln, but today I started it up in the morning and was in the studio in the evening and got to see exactly what was happening during the cooling cycle. I do a slightly-slow cooling cycle to even out the results in my 3 kilns because they all cool at drastically different rates due to their sizes. I do a drop from the peak down to 2000F, then cool at 175F/hr down to 1500F. This gives me identical results from all 3 of my kilns. This firing I'm talking about here is in my 10 cubic foot L&L EQ2827-3, which has 3 zones, and was packed very tight in the middle. I was surprised at just how much slower the middle cools compared to the top and bottom. This photo shows how it's going part way through the initial drop from peak temp to 2000F:

As you can see, the middle and the top are nowhere close to each other. In a normal firing segment, a 73 degree difference would stop the firing with an error code. So why isn't it doing that here? It's because the cooling rate is set at 9999, or full speed. Any time you use 9999, whether it's climbing or dropping, the controller lets the kiln do its thing and doesn't care if the sections aren't even. Firing up or down at 9999 is the fastest, but you sacrifice evenness. As the temp continues to drop, we see this:

Here you can see that the top section (TC1) has started firing again. The set point for this segment was 2000F, at which point it should start cooling at 175F/hr, yet the top section passed that by about 20 degrees before the relay kicked on and the controller stopped the drop. Why did it let it get so far below the set point? Because it's averaging the 3 zones. Once the average of the 3 zones hits the set point it will start to fire each section again as needed to match the set point.
I get a lot of questions from customers about error codes and cooling cycles. The biggest problem is that the kiln can't always keep up with the programmed cooling rate. There are a number of firing schedules out there on the internet that people are trying that use a rate of 600F/hr or more for the fast drop portion of the cooling cycle, and many kilns simply cannot cool that fast, especially the middle section. When you have a specific rate programmed, the controller will send out an error code if the kiln can't keep up with that rate. So if you want a really fast drop you should use 9999F/hr, not a specific rate. For most people doing slow cooling with cone 6 work it won't matter if the sections are not totally even during the drop. If you do need more precision, like if you're firing crystalline work and it's important that you don't overshoot any target temps, then you'll want to put in a slower drop rate that the kiln can actually keep up with, and the controller will keep the sections even and not overshoot set points.

The digital fire link seems a pretty good example of the difference a smaller mesh can make.
 
The smaller the better in my opinion for melting silica. I remember back to my bubble experiments and removing quartz/silica additions and trying to source from feldspars/clays always had a better melt. Glazenerd did send me some super fine silica that is still on my list to test about 7 years later 

The digital fire link seems a pretty good example of the difference a smaller mesh can make.
 
The smaller the better in my opinion for melting silica. I remember back to my bubble experiments and removing quartz/silica additions and trying to source from feldspars/clays always had a better melt. Glazenerd did send me some super fine silica that is still on my list to test about 7 years later 

Crazing to me is a result of the differences in the rate of growth or shrinkage. Once fired clay and glaze  are the same size, so the clay has shrunk to what it will be and the rate of future expansion and contraction will be affected by its composition and its  physical (and thermal) properties such as density etc…. Firing the body to its rated cone will provide the best chance of a fully melted body with repeatable characteristics. So the COE will likely be different for a cone 6 body fired to cone 4 or even cone 5. Our glaze on the other hand if able, may tolerate the difference in speed of expansion / contraction  and not fail or craze as if pulled apart. As a glaze is fired higher will its COE change? Very likely yes. Will its physical characteristics change? Very likely yes. Glazes more resistant to wear as in surface hardness may fail more so in impact. 
I think the difference here for me, none of this is about the starting size and all about rates and whether the glaze can keep the clay body in a slight bit of compression without the glaze failing. So firing both to their rated cone likely gives the best repeatable representation of the match for both. Firing lower and assuming the next cone higher will improve the COE match between the clay and glaze is likely not really reliable in my view. So in the end, fire to rated cone, firing to lower cones is very likely not a good indicator for how these materials react when fired to rated cone.

I think hard to generalize and no way to guarantee anything is craze free forever. I do think there is reasonable correlation though. Differences in the expansion rate of clay and glaze being the prime issue, followed by the long term reliance of the glaze to tolerate the slight inevitable difference. The fired COE is often a result of fully firing so a clay body or glaze not fired or fully melted may have a different COE than one that is. Just imagine a clay body or glaze under fired by two or thee cones, we would normally expect it to behave very differently than fully fired stuff because it is under fired. If both are under fired the same amount will their under developed  COE somehow be even between them?  While I think in the ranges you are working in, likely a decent indication, just firing hotter does not necessarily mean the glaze will have greater flexibility and could actually become harder and more prone to tensile failure.
I think your logic is reasonable, but believe it’s always best to test the the clay and glaze combination fired to cone.

I'm not convinced there's much evidence that 0.3:0.7 is the most durable ratio. I mean even in that ratio there's so many different fluxes included that there's too many variables for it to be a useful rule.

Thanks to you knowledgeable folk my little kiln is now happily ramping up at sonic speed again.  It was indeed damp!!  I propped the lid (which was only possible as I bypassed the lid safety - @High Bridge Pottery (which is the silver box with the cable tied wires) and then I stuck my heat gun nozzle in the bung hole - it fitted perfectly!  Ran it a few times for 5 minutes and each time I lifted the lid tiny little steam clouds puffed out!!! 
 
I am so relieved I don’t have to explore the RCD or current leakage issue just yet!  But fyi my cooker has its own dedicated fuse but it’s still protected by the RCD. 
now I’m debating if I should hook up the lid switch or leave it out as I quite like the idea of propping the lid to reduce the speed the kiln heats up but I do t like the idea of accidentally touching the elements when the kilns power is on…….  i guess I would only make that mistake once…… 
I will never leave the lid open or off for anything (other than loading and unloading) ever again!  
 
thanks again everyone 

 

I just had to find the full document: https://aura.alfred.edu/server/api/core/bitstreams/182c2504-e6ac-42f7-bb12-34492c950d5f/content
 

I'm not convinced there's much evidence that 0.3:0.7 is the most durable ratio. I mean even in that ratio there's so many different fluxes included that there's too many variables for it to be a useful rule.

I tried to explode a cup in the microwave. The test was to see if a cup with water absorbed into the body would explode when microwaved. My cup got really hot, but did not explode.
I started with two nearly identical cups made from a white stoneware with an estimated absorption of 3.7% as previously measured with test bars. Each cup has a foot ring and was glazed inside and out with a clear glaze. The foot ring and the bottom area inside the foot ring was not glazed.
One cup was set aside and was not subjected to any water.  It weighed 433.9g.
For the other cup, I kept it upside down on my desk and kept filling the area inside of the foot ring with water for a few weeks. My thought is this would simulate water absorption from being subject to multiple rounds in a dishwasher. Periodically, I would check its weight. After a couple of weeks, the water absorption stabilized and the weight of the cup went from 426.0 grams to 441.8 grams, a gain of 15.8g or about 3.7% (which matches my test bar estimate). This means it absorbed about a tablespoon of water. It did not gain any additional weight/water with more time beyond a couple of weeks.
Then, I microwaved both cups (both empty) at the same time in a 1.4kw microwave with rotating platform for 15 minutes. I very quickly measured their temperature after each minute of microwaving. The cup with absorbed water reached a maximum temperature of 433F. The cup without absorbed water maxed at 250F. Neither exploded. The cup with absorbed water crazed, but no other damage.  The cup with no absorbed water did not craze and was not damaged. The graph shows the temperature in degrees Fahrenheit over time in minutes.
After microwaving letting the cups cool, I remeasured their weight. The cup with water applied went down to 425.4g indicating that all of the water was boiled out. The cup without applied water was 425.3. After microwaving, both cups weighed a less than their original weights.
So, I was not able to explode my cup. This does not mean that your cup won't explode. This was for one particular clay and may not be representative of other clay bodies.  If others have time, it would be interesting to repeat the test with other clay bodies.
Notes: Microwaving empty pieces is not recommended because it might damage the microwave oven.  I use an old microwave that I don’t care if it breaks. I used an infrared Infrared Thermometer Temperature Gun to be able to very quickly measure the temps. If you decide to repeat this experiment, note that I got 30F difference between the top and the bottom of the cup and averaged the reading.

100% agree

I appreciate this question. As well as the notion that simple frit and clay glazes are best . 
In the 2016 paper, Matt refers back to the 2012 presentation, discussing results of 0.5 R20:0.5 RO samples in relation to boron. He concludes that paragraph with:
“Thus the quality of glazes is not dependent on any specific temperature for durability. Chemistry is the only relevant factor.”
Obviously, temperature does matter, if a glaze hasn’t melted it’s not complete. But once it has fully melted, why would a glaze that’s durable at cone 04 (say, 0.3 R2O:0.7 RO, 0.5 boron) be less durable if fired to cone 6? It might run all over, but that’s a different problem. 

It's saying the temperature is too low to read. I would try swapping around the wires if you wired the thermocouple plug, or maybe it's a loose connection.

@PeterH @Clay17 @neilestrick @Dick White @Bill Kielb Just "finished" the site (or at least the major features). I'm sure there are some bugs to be ironed out, but so far it's working for me and for the files you all sent me (many thanks).
If any of you guys end up playing around with it and find any issues, let me know. Planning on trying to get the word out in the next few weeks and want to catch as many bugs as I can. 
www.fire-graph.com
 

Thanks Min, I think the issue was Epsom solution not saturated enough. I have made a new Epsom solution and results are promising. Thanks for all your help  much appreciated 

I was doing a bit of reading and stumbled across a new Stull chart. He seems to be doing the same experiment but at cone9 instead of cone11. It is interesting that the OG Stull chart is cone11 but everybody uses it at any cone.
This time he is glazing tiles and making the glaze into cones to see the deformation temperature. The solid line AB is his same “best gloss line”. The dashed line CD passes through the lowest deformation temperature in relation to Silica and the dotted line EF the same for Alumina.
 

 
He then goes on to plot it on top of the original Stull chart but misses out his new gloss line so I have done my best to add it back in blue.
 

 
It’s interesting how different the best gloss lines are. I tried adding on Silica:Alumina ratios but I haven’t had any good ideas yet. The wiggly silica line and shape of the deformation eutectic look like they tell me something but I haven’t figured anything out.
 

 
If you want to read the paper - Deformation temperatures of some porcelain glazes – R.T Stull and W. L Howat. Transactions of the American Ceramic Society Volume 16. Page 454. Copyright 1914 by Edward Orton Jr Edward Orton Jr - https://archive.org/details/transactio16amer/page/454/mode/1up

I was talking to a guy at work who did some glaze leach testing with lead glazes and grapefruit juice. They were getting really high lead readings but it turned out to be the grapefruits being grown near a road and nothing to do with the lead glaze. As safe as we can make a glaze a lot of the food/drink we put in is contaminated 

I was doing a bit of reading and stumbled across a new Stull chart. He seems to be doing the same experiment but at cone9 instead of cone11. It is interesting that the OG Stull chart is cone11 but everybody uses it at any cone.
This time he is glazing tiles and making the glaze into cones to see the deformation temperature. The solid line AB is his same “best gloss line”. The dashed line CD passes through the lowest deformation temperature in relation to Silica and the dotted line EF the same for Alumina.
 

 
He then goes on to plot it on top of the original Stull chart but misses out his new gloss line so I have done my best to add it back in blue.
 

 
It’s interesting how different the best gloss lines are. I tried adding on Silica:Alumina ratios but I haven’t had any good ideas yet. The wiggly silica line and shape of the deformation eutectic look like they tell me something but I haven’t figured anything out.
 

 
If you want to read the paper - Deformation temperatures of some porcelain glazes – R.T Stull and W. L Howat. Transactions of the American Ceramic Society Volume 16. Page 454. Copyright 1914 by Edward Orton Jr Edward Orton Jr - https://archive.org/details/transactio16amer/page/454/mode/1up

I was doing a bit of reading and stumbled across a new Stull chart. He seems to be doing the same experiment but at cone9 instead of cone11. It is interesting that the OG Stull chart is cone11 but everybody uses it at any cone.
This time he is glazing tiles and making the glaze into cones to see the deformation temperature. The solid line AB is his same “best gloss line”. The dashed line CD passes through the lowest deformation temperature in relation to Silica and the dotted line EF the same for Alumina.
 

 
He then goes on to plot it on top of the original Stull chart but misses out his new gloss line so I have done my best to add it back in blue.
 

 
It’s interesting how different the best gloss lines are. I tried adding on Silica:Alumina ratios but I haven’t had any good ideas yet. The wiggly silica line and shape of the deformation eutectic look like they tell me something but I haven’t figured anything out.
 

 
If you want to read the paper - Deformation temperatures of some porcelain glazes – R.T Stull and W. L Howat. Transactions of the American Ceramic Society Volume 16. Page 454. Copyright 1914 by Edward Orton Jr Edward Orton Jr - https://archive.org/details/transactio16amer/page/454/mode/1up

I was talking to a guy at work who did some glaze leach testing with lead glazes and grapefruit juice. They were getting really high lead readings but it turned out to be the grapefruits being grown near a road and nothing to do with the lead glaze. As safe as we can make a glaze a lot of the food/drink we put in is contaminated 

My glaze firings have always been quicker than bisque. It would be weird if you are firing on exactly the same settings but I am guessing you turn up the glaze firing faster?

I was talking to a guy at work who did some glaze leach testing with lead glazes and grapefruit juice. They were getting really high lead readings but it turned out to be the grapefruits being grown near a road and nothing to do with the lead glaze. As safe as we can make a glaze a lot of the food/drink we put in is contaminated 

There's 1000kb limit per post but most csv files should be way under that.
 
I would prefer the x-axis in hours and another option for easier seeing of the firing is to dash the setpoint line so it covers less of the firing curve.

There had been discrepancies in Orton's online materials regarding small cone deformation temperatures*.
I used small cones for the kiln sitter (prior kiln), and I like them. They are a tiny bit cheaper.
Here's an excerpt from the message I received from Orton Engineer (circa March 2020):
Dear Sir,   Thank you for contacting Orton to draw our attention to some incorrect information on our website.  The small cones do in fact deform after the large cones.  We have updated the information on the website.    See also this thread (start at the bottom/end) Kiln Sitter cone for witness cone - Studio Operations and Making Work - Ceramic Arts Daily Community   *There still are! The 2016 cone charts are all "backward"   See the small cone page, SMALL CONES | Orton Ceramic
"Small Cones used on the kiln shelf deform at about 9°F after Large or Self-Supporting Cones of the same number." It's just because the small ones are smaller - the cones are same material; same reason a large candle will slump in hot weather before a small one.