SunsetBay
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Posts posted by SunsetBay
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2 hours ago, Bill Kielb said:
@SunsetBay Interesting recipe, I assume the fluxes and or feldspar have been left out. Usually 10 -15% clay is enough to keep things suspended. Up to 2% bentonite can be traditionally added to assist with the suspension when there is not enough clay to keep things suspended. These recipes seem to have more than enough clay, so why the bentonite at its typical maximum? Sometimes it’s needed, often times it’s just the result of passing a recipe onward and never removing it. Bentonite really shouldn’t add to the fired result. So, you may be able to reduce or eliminate it eventually and you have so much EPK that calcining a portion of it could improve its ease of application and reduce its tendency to crawl. Looks like 10 - 15% of the EPK could easily be calcined and tested to see if this behaves more to your liking.
I'm not sure why the bentonite is there. I think these are the versions of these glazes from John Britt's Cone ^6 glaze book. Pretty much all his glazes add bentonite. These two glazes are originally from Roy & Hesselberth's Mastering Cone 6 Glazes, and I can't recall if they included bentonite. I have to say that both these glazes tend to settle and gel really quickly. They need to be mixed a lot before glazing, and often again between individual pieces. In case you're curious, here are the recipes:
Variegated Slate Blue
Neph Sy 4%
Silica 17%
EPK 30%
Wollastonite 29%
Frit 3195 20%
Total base: 100%
Add:
Cobalt Carbonite 1.5%
Copper Carbonite 3%
Rutile 6%
Bentonite 2%Spearmint
Neph Sy 4%
Silica 17%
EPK 28%
Wollastonite 28%
Frit 3195 23%
Total base: 100%
Add:
Copper Carbonate 4%
Rutile 6%
Bentonite 2%
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14 hours ago, Min said:
+1 for what Bill said.
There are a couple versions of the Mc6G Licorice glaze since the original had a fair bit of EPK in it which caused crawling for some people when it was applied heavily. One of the altered versions used calcined epk for part of the total epk and the other used a combo of epk plus some ball clay. How much clay is in the Spearmint and Varigated Slate Blue? Recipe versions that you are using?
Spearmint: 28% EPK, no ball clay, 2% bentonite
Variegated Slate Blue: 30% EPK, no ball clay, 2% bentonite
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52 minutes ago, Bill Kielb said:
Crawling is usually a function of the fired surface tension (how well a glaze can heal) so most influenced by application: thickness, cracks while drying ….. and less influenced by firing schedule. Some glazes tend to crawl while others heal really well. I would look at application as the likely culprit.
I'm kind of guessing that, because it's happened before. I'm wondering if I should use a bit of Darvan or sodium silicate to adjust the viscosity slightly without changing the specific gravity, and also do a faster dip.
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On 9/12/2023 at 10:01 PM, neilestrick said:
I just looked at my 10 cubic foot kiln, which is going through a cone 6 firing with a controlled cooling. It's at about 1935F, cooling at a rate of 175/hr. The top is running at 25%, the middle and bottom are at 0%. This makes sense since the top loses a lot of heat out the lid. All 3 are very close to the traveling set point, so it's staying on schedule. But it means that about 175/hr is the fastest it can cool at this point. If it was programmed for 500/hr cooling, it might error because it can't cool that fast. It all depends on how quickly it gets too out of sync with the traveling set point.
Time passes....
Just checked it again. Set point is at 1788. Top is at 20%, bottom is at 8%, both are even with the set point. Middle is at 0% but 30 degrees above the set point. The middle cannot maintain the 175/hr cooling rate at this temperature. I never get an error code with this schedule, so I know it'll stay within the acceptable parameters, but it's definitely lagging there.
I don't know how I missed this reply, Neil. I'm just found it now. Honestly, though, I'm not sure what to do with it. It sounds to me like what I should do is try the schedule you outlined in one of your earlier replies. I did just fire the kiln with the Mastering Cone 6 Glazes recommended schedule, and the pieces that used the spearmint and variegated slate blue glazes crawled a fair amount. I did prefer the slight flattening (or "mattening" !!!) of the surface, but I'll now have to refire them to correct for the crawling. Problem is, I'm not sure what caused the crawling: Dips too long, or something about the firing schedule. Any insight would be welcome. I hope to refire in the next few days. (Since I liked the results in my test kiln, maybe I'll just stick a few mugs in there and try refiring them that way, but I'd really like to get a handle on this with my large kiln.) Thanks.
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2 hours ago, neilestrick said:
We are dealing with 2 different functions here. One is a controlled cooling, so that the kilns cool at the same rate and give you the same results. 175/hr (or probably even 200/hr in your kiln since it's not too big) will give you a controlled cooling that's not too far off from the natural cooling speed. But by programming that into both kilns, you get identical firings.
The other is a slow cooling, which is done to increase crystal growth and color development in glazes. This is typically done from 1900F down to 1500F.
Your e23 does not cool slowly enough to give you the same results as a slow cooling program. You need to cool slowly from 1900F down to 1500F in order for the matte glazes to go more matte. I would start with 150F/hr through that range and see how it goes. So if you want a slow cooling and you want identical controlled cooling:
1. Use whatever program you want going up to cone 6. If you want to use the pre-programmed cone 6 medium or whatever, either look that up and plug it into a Vary-Fire/Custom firing slot, or if you have a Genesis controller, copy the program into a custom slot. Then add the following steps:
2. 9999 to 2132. This is a 100 degree drop from cone 6, to set the glazes before you start a controlled cooling. If you do the controlled cooling from the peak temp, you'll get extra heatwork.
3. 175 or 200/hr to 1900. This is the controlled cooling section that will keep your kilns cooling at the same rate. If you don't need a slow cooling cycle for the the glazes, then take this down to 1500 instead of 1900 and make it the final step.
4. 150/hr to 1500. This is the slow cooling section that will encourage crystal growth to increase mattness and color development in some glazes. The slower this goes, the more pronounced the effect will be. 150/hr is a good starting point, though.
175/hr vs 150/hr doesn't seem like much, but I've seen a big difference in my glazes. If you try to program the controlled cooling at to fast a rate, the kiln won't be able to cool that fast and you'll get an error code. My e28T need 175/hr to avoid that. Your e23 may be able to handle 200/hr, though, since it's smaller.
That is all super helpful, Neil, thanks. I do understand the difference between controlled cooling and slow cooling. But between trying to figure out which slow-cool program to try and how to get the two kilns to match it as closely as possible, I was getting confused.
My schedule (and my impatience) made me get the little kiln going before I saw your message. I decided to use the schedule suggested by the authors of the glaze recipes. It calls for a drop from peak temp of 500 degrees/hr to 1900 degrees, and then another drop of 125 degrees/hr to 1400 degrees. If I'm not satisfied with how the glazes look with that program, I'll try yours.
Thanks again for your help and detailed explanations.
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2 hours ago, neilestrick said:
The schedule I posted is for if you're not using a specific slow-cooling cycle. The goal is not necessarily to match the big kilns cooling cycle, because that is not linear. Instead, put them both on a cooling cycle that allows them to cool at the same rate that's not too far off from the big kiln, without necessarily being a 'slow-cool' cycle that will affect the glazes. 175/hr seems to do that. We drop down 100 degrees first so that the controlled cooling doesn't add heatwork to the glazes. If you cool from the peak, you'll get additional melt in the glazes.
If you want to do a 'slow-cool' cycle that affects the glazes, those usually start at 1900F after natural cooling, and slow cool to 1500F. You may be able to let both kilns naturally cool to 1900F and then slow cool, but you'd have to test your glazes and see if they come out the same or not. If they don't come out the same, do the 100F drop, then cool at 175/hr to 1900F, then slow cool at whatever rate you want down to 1500.
My E23 cools fairly slowly due to the 3" bricks, but I'm trying to get some semi-matte glazes to look more matte. I've succeeded in the past, but more by accident, so I don't really know what I did to make them work like that. I've used both the pre-programmed slow ^6 and the slow ^5 (with various holds), but those glazes are still coming out glossy. Since these are Mastering Cone 6 Glazes recipes (spearmint and variegated slate blue), I thought I should try Ron Roy and John Hesselberth's suggested firing schedule, but I've been concerned that if I just program that into the Bartlett controller on my test kiln, it won't match the results with the same program on my E23. I'm now thinking that maybe I should just try the test firing with the MC6G schedule and see how the results differ from what I've been doing in my big kiln and go from there. Thanks again for your help. I wish this stuff didn't make my head spin.
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On 9/6/2023 at 11:08 PM, neilestrick said:
Use the same firing schedule going up, then add a cooling cycle that goes full speed cool (rate 9999) down to 100 degrees below the peak temp, then a rate of 175/hr down to 1500. You'll get the same results from both kilns. I've been using this schedule for years for 3 kilns of different sizes (test, 4 cu/ft, 10 cu/ft).
Shouldn't the goal temps in the small kiln's slow-cool cycle match the temps of the big kiln's slow-cool cycle?
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13 minutes ago, Dick White said:
The new small kiln will not fire faster than the big one, as the firing up speed is managed by the digital controller. However, the little kiln will cool much much much! faster than the E23. The glossiest glazes are not affected by the cooling rate, they will be glossy even in a slower cool. Glazes that are expected to be less glossy or matte achieve their surface during the cooling, and if the cooling is too fast, the nice microcrystalline surface will not develop. A large kiln such as your E23 will retain heat better (larger size, more thermal mass inside from more ware and shelves) and the less glossy glazes will often be nice enough (though probably more interesting if you program a slow cool). With the test kiln cooling so fast, everything will be glossy. All is not lost - program it for a slow cool and the controller will manage the cool-down for you.
The nuance here is that the conventional programmed slow cooling will be slower than the big E23's natural "just turn it off" cooling, so you are still going to get different outcomes between the two kilns - unless you a) program both kilns with the same cool down sequence, or b) get some diagnostic equipment to precisely document the minute-by-minute natural cooling performance of the E23 and replicate that in a custom program for the little kiln.
I figured I'd have to use the same slow cool for both, but I feel like I remembered reading somewhere that because of the differences in the kiln, I'd have to tweak the program for the smaller one in some way to end up with similar results.
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My regular kiln is an L&L E23T-3. My new test kiln is an L&L DLH11-DX. I haven't used it yet, but I'm almost ready to try firing a bunch of test tiles. Is there anything I should do in terms of programming the small kiln in order to get as close as possible to what I might expect from firing the large kiln?
Firing schedules: Large kiln vs test kiln
in Equipment Use and Repair
Posted
Thanks! I'd love to know why you made the changes you made, and if you have any photos.