Gonepotty
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Posts posted by Gonepotty
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On 4/19/2024 at 3:09 PM, neilestrick said:
You can do a thermocouple offset which will affect all temperatures, or a cone offset to change the final temp of a specific cone. Using the pre-programmed firing schedule (I'd use Medium speed) will give you a better idea of how accurately the system is firing compared to a custom schedule.
If I do a cone offset will this only be effective if I fire using a preloaded cone programme? Don't think I want to offset thermocouple as my glaze firings are fine. I have a smaller kiln which has a S type thermocouple and its always spot on. - think i might consider upgrading mine when it comes to end of its life.
Next bisque firing I'll try the preloaded cone 08 on medium speed as see how things go. Thanks so much for your help
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20 hours ago, High Bridge Pottery said:
Is it frustrating because it is causing problems or just because you would like the cones to read the same numbers? If it's the second I wouldn't worry about it.
Neither of those schedules you have posted are aggressive. For me 100c per hour is slow, 200c fast and 250c is aggressive.
I bisque to cone 016/017 (that's a guess, I have never put a cone in a bisque kiln) in 4 hours doing 20 min to 100c, hold for 20 min, then ramp at 250c an hour up to 800c and hold for 20 min. You can see the kiln drop to under 250c an hour while it struggles from 500-600c as chemical water is lost but it catches back up to 250c and hour after that.
Thanks for your reply. Not having any problems with the pots but rather feel that its not achieving the desired bisque of 950'C - trying to keep everything consistent so I know how the glazes will behave when applying and during the firing
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23 hours ago, oldlady said:
your kiln manufacturer has a long history of getting the best out of it's kilns and providing simple controls for users. why do you think your program is necessary and better than theirs? and what is special about cone 09? yours is the first post to mention it in all the years i have read almost every post. are you glazing some special way that requires your bisque so soft?
once you fix the loading as suggested, just try what Neil, who is a kiln specialist and dealer, suggests.
Thanks for your message. I am going to try the preloaded cone 08 bisque firing next.
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On 4/17/2024 at 6:06 PM, neilestrick said:
Pack the middle the tightest.
Have you tried just using the cone 08 preprogrammed firing schedule?
Thanks Neil, this was my next thing to try
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5 hours ago, Min said:
As much of the density or mass in a firing comes from the shelves themselves it's often helpful to put the taller pots on the bottom shelf, shorter pots and more shelves in the middle of the kiln and tall again on the top shelf. (assuming it has with just one thermocouple or is a manual kiln)
Thanks Min, yes it only has 1 thermocouple. I'll make note of this info for my next bisque firing
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5 hours ago, Pres said:
Density of the load has an effect on the way heat moves in the kiln. Kilns are heated by 3 different forms of heat transfer: Radiant, Conduction, and Convection. Understanding these will help you to understand the need to pack the kiln consistently. Radiant heat is occurs first in the kiln as the elements radiate heat to heat up the air and the pottery. The pottery on the outer edges will heat up to radiate heat towards the center of the kiln. Please note that while Radiant heat is going on Convection is also occurring in the kiln as air heats up and begins to move to the top of the kiln forcing cooler air downward. Overly tight loads will inhibit the movement of air in the kiln causing areas that do not get air to not reach expected cones. However, as this is going on Conduction, where heat is moving through a solid, is taking place, Conduction is a slower process but it allows the pots to heat up from the outside to the inside, and the kiln from the inside to the outside. This good reason to have proper distance from the kiln to outside walls or other materials that could ignite.
Hope this helps to answer some of you concerns.
best,
Pres
Thanks so much Pres, super helpful information and great explanation. Feel more confident now with bisque firing
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10 hours ago, Babs said:
Not knowing the clay you use, or the kiln, here's my bisque in °C.
And, Callie the expert, so listen to her.
If bisqueware dry and of good thickness i.e not thick sculpted pieces
50°C / hr to 100°C
100°C/hr to 600°C
150°C/hr to 1000°C
Soak for 10 minutes.
Target is C06.
I pack bottom shelf with taller stuff, rest of kiln is tumble packed. Soak at end for me is to allow kiln temp to even out and tumble stacked ware to get to the cone target.
Seems brutal but works
Thanks Babs, its really helpful to have many reference points/info from different folks as it helps build a bigger picture for me.
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14 hours ago, Callie Beller Diesel said:
Yes. Yes this will affect things. If your kiln is hottest on the bottom and you’ve packed it tightly, but your ware still isn’t getting the heat, the bottom is probably packed too tightly. You may also be going a bit too fast through the middle parts of that firing. 120 C is a really fast rate of climb. And yes, it’s not unusual for a bisque to go for 10-12 hours. Keep in mind the elements aren’t on at full power the whole time. If you’ve got the touchscreen, check out the diagnostics in the last firing. It’ll tell you what your energy usage is.
Re: the density affecting the heat: Electric kilns are sometimes programmed to emit more heat on the bottom elements, because heat rises, and they’re trying to avoid cool spots in the bottom of the kiln. They’re assuming people pack it evenly, and they don’t expect consumers to have to compensate their loading habits on a new kiln.
If the bottom part of the kiln is packed particularly densely, especially compared to the other shelves, the heat may not have time to penetrate all the way through to the middle of the bottom layer. If the cones aren’t bending on that bottom shelf with a 20 minute soak at the end, that bottom layer and even the middle is probably playing catchup to even hit cone 09. Try slowing your second segment to 90 or 100 degrees C, aiming for the proper cone 08 temperature, and packing the kiln more evenly.
Thanks so much for your repl
14 hours ago, Callie Beller Diesel said:Yes. Yes this will affect things. If your kiln is hottest on the bottom and you’ve packed it tightly, but your ware still isn’t getting the heat, the bottom is probably packed too tightly. You may also be going a bit too fast through the middle parts of that firing. 120 C is a really fast rate of climb. And yes, it’s not unusual for a bisque to go for 10-12 hours. Keep in mind the elements aren’t on at full power the whole time. If you’ve got the touchscreen, check out the diagnostics in the last firing. It’ll tell you what your energy usage is.
Re: the density affecting the heat: Electric kilns are sometimes programmed to emit more heat on the bottom elements, because heat rises, and they’re trying to avoid cool spots in the bottom of the kiln. They’re assuming people pack it evenly, and they don’t expect consumers to have to compensate their loading habits on a new kiln.
If the bottom part of the kiln is packed particularly densely, especially compared to the other shelves, the heat may not have time to penetrate all the way through to the middle of the bottom layer. If the cones aren’t bending on that bottom shelf with a 20 minute soak at the end, that bottom layer and even the middle is probably playing catchup to even hit cone 09. Try slowing your second segment to 90 or 100 degrees C, aiming for the proper cone 08 temperature, and packing the kiln more evenly.
Thanks so much for your help. I think I'll adjust the firing schedule and make sure I pack it evenly! Really appreciate you taking your time to reply
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56 minutes ago, Pres said:
@Gonepotty, could you include a little more information on your kiln. Are you doing a manual ramp with a kiln setter, or are you using a programmable controller. Balanced packing on all shelves will help with evening out the temperatures, so yes having a tighter pack in the bottom will effect the firing.
best,
Pres
Hi Pres, I used a programmable controller. Skutt 1027 with the new touch screen controller. Would you mind explaining how a tighter packed shelf will impact heat as this is something I am struggling to grasp. Thanks so much
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Hi all,
Having very frustrating results with my bisque firing . oxidation. Never seems to get to target temp...elements fine, glaze firing reaches target with no issues.
Current 08 schedule ( Celcius)
Step1) 80'C/hr to 200.
Step2)120'C/hr to 915
Step3)60'C/hr to 995 +20min hold. (aiming for top target of approx 1015'C; kiln has always seemed to fire cooler for bisque by about 65'C hence aiming for this higher target in the hopes it will reach 950'C).
RESULTS: Top shelf reached 08. Mid shelf reached 09. Bottom shelf … no bend to 09. Bottom shelf was densely packed...would this impact the firing.? Typically, my kiln is hottest on bottom shelf and coolest ontop. Was a ful kiln load with shelves and props.
I have tried this below schedule in the past and worked quite well. It is listed as a "high bisque" schedule but wondering if it is too aggressive?:
1)90'C to 300
2) 110'C to 900
3) 60'C to 1050+ 20min hold.
whilst I was quite happy with this programme, it fired a bit too hot for my bisque ware and reached 1000'C. I would like to aim for 950'C and so thought shall I:
a) drop the final temp down to 1000'C+20min hold in the hope that it will reach 950'C? OR
b) adjust the programme to the 08 schedule?
Should bisque firings take longer than 10hrs? First firing schedule took 9.5hrs whilst the "high bisque" schedule takes 13.5hrs...Guess I was keen to also reduce firing time but it appears to not have worked that well.
Any words of wisdom greatly appreciated!
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Thanks everyone for your help
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On 1/4/2024 at 2:55 PM, Roberta12 said:
Would your terracotta pot be able to withstand bisque temperatures?
I have no idea…I don’t use terracotta so was going to use a pot from the garden centre
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13 hours ago, Callie Beller Diesel said:
Any container going into your next bisque will work. I wouldn’t trust commercial terracotta, just on the basis you don’t know what temp it’ll melt at for sure.
Would it work if I used a greenaware pot?
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Hi all,
need to make some calcined clay . Don’t have a bisqued vessel to put the EPK in…would an unglazed terracotta pot be alright?? Or any other ideas
thanks so much,
kathryn
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On 12/15/2023 at 2:49 PM, Hulk said:
"Which do I use ?"
Hard to say.
I'm guessing the larger the container - the larger the mass of glaze - the longer it would spin before stopping, everything else being equal - perhaps due to more mass per unit surface area of the bucket interior, which provides the drag? Easy enough to test; mix thoroughly, pour some off to a smaller bucket, re-test.My experience is with different glazes and two gallon buckets.
However, I've good results with tweaking the specific gravity and thixotropy of every glaze I've tried.
Two of my glazes I don't add any Epsom salt too at all; they gel great as is.Added: 21 liters is just over 5.5 gallons, that's a lot of glaze
The smaller batch seemed to have better “bounce back “ and seemed uniform with Tony Hansens demonstration. Yes it’s a huge amount of glaze…think I’ll go smaller next time!
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5 hours ago, C.Banks said:
Hi Gonepotty,
I'll go back to lurking - better to remain silent and all that
I appreciate any help :)) thanks for your support
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1 hour ago, C.Banks said:
So in the interest of clarity: 21litres can look a lot like 2 litres to tired eyes
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3 hours ago, Min said:12 000 gram batch of glaze, made up approx 21 L which would be just over 4 1/2 Imperial gallons of glaze. Recipe contains china clay (grolleg?) at 15% so it shouldn't be hard-panning. 5 tablespoons of saturated epsom salts solution added but glaze slurry still leaving heavy drip marks. Typical amount of epsom salts solution would be in the range of 1 tsp per US gallon (0.8 of an Imperial gallon)
Has the efficacy of the epsom salts solution been tested? Have you tried a new saturated solution?
Is the method of dipping the pots part of the issue? Is this a clear glaze high fire? How are the drips with a lower sg? How does the glaze look when fired with a lower sg?
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
- Hulk and High Bridge Pottery
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1 hour ago, Callie Beller Diesel said:
Your saturated epsom salt solution is dissolved. Your glaze is a suspension*.
Dissolved is not the same as suspended. Dissolved is like when you make a simple sugar syrup or saline: the sugar or salt particles become indistinct from the liquid. A suspension is when the particles stay distinct from the liquid it’s in, but stay more or less dispersed throughout. A suspension may settle out over time, or be re-suspended when you stir it up. A solution won’t loose the original materials out of it, unless it changes temperature or some of the water evaporates out of it.
*a glaze can sometimes be a combination of a suspension and a solution if some of the materials do actually dissolve into the water of the glaze over time. The boron in things like gerstley borate or some frits are known for being soluble in glaze buckets, as are a few other things. This process tends to take a few days or even weeks, and when it happens, the now-solution part of the glaze helps keep the other dry particles suspended. This is also called gelling or flocculating. When you add epsom salt solution to a glaze bucket, you’re either creating this effect in a glaze that has no (or negligible) soluble materials, or accelerating it in a recipe that has some solubles.
Unless your glaze has turned to the consistency of something like skyr or Greek yogurt, you have not ruined it with the amount of epsom salt solution you've added. Single cream is kinda sorta the ballpark of what you want a glaze consistency to start at, but you’re still having some settling. Your description of your glaze’s behaviour with the epsom salt says you might need to add more. But there’s some question about the amount you’ve already added.
Is your epsom salt solution super saturated, or did you dissolve some in some hot water and go from there? A super saturated solution is made by adding Epsom to boiling water from the kettle until you can’t dissolve any more. You will need a surprising amount for this. There should be some crystals at the bottom of the container that won’t dissolve easily while still hot, and as the solution cools, some more crystals should appear at the bottom. The resulting solution will be clear, but will refract light in an almost oily way. It’ll also eat through metal lids over time, so if your storage jar has a metal lid, line it with a bit of cling film.
If your solution isn’t super saturated, that could account for the seemingly large volume not giving you the desired effect. If that’s the case, you do have some room to add more. You also have to mix quite thoroughly to give the effect a chance to work.
A cautious method to test if adding more would help or go too far is to remove a sample from the bucket and add flocculant to it by drops, mixing well between additions.
This is such brilliant information - thanks so much for taking your time to help and explain. Really appreciated. I suspect the Epsom solution wasn’t saturated enough so I mixed up a new batch and this has helped a lot. Much better consistency and better glaze application. I’ll test a couple pieces in next firing.
thanks again
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On 12/15/2023 at 4:17 PM, Mark C. said:
(This sounds like a lot.)
a tablespoon or two is plenty for a 10,000 gram batch
5 tablespoons is way to much for 3,000 grams-it will be thick soup
Hi Mark, I have add 5 tablespoons to a 21L batch.
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40 minutes ago, Callie Beller Diesel said:
Don’t get too hung up on specific SG numbers. The number that works is the one that gets the right application of glaze YOU want on your pot, and that might be different than what someone else recommends. The 1.4 mark is a rough starting point, kind of like seasonings in a recipe. Some people will want more, some people will want less.
First, water is the easiest thing to adjust in a glaze, and adding things like epsom or darvan to adjust how a glaze flows should be done only after you’ve determined it’s really necessary for getting the right glaze application. If the bucket has a layer of glaze materials in the bottom within 5 minutes of mixing, pulling out the epsom salt solution is the right thing to do.
Adding epsom salts will flocculate a glaze, or make it gel slightly. This is why the glaze now seems thicker than it did, and it may leave a more generous layer on the pot than the same 3 second dip would without the flocculation. You might notice on some glazes it will start to crack while drying, potentially causing crawling in the kiln. And yes, it will also slow your drying time. That slowed drying can help smooth out application based drip marks. If your glaze is one that might be subject to crawling due to application, adding water will help resolve that. But know that adding water to a glaze that’s already flocculated will further delay drying. It may mean you have to adjust your workflow to allow for that, but it’s worth it if it means the glaze goes on the pot nicely.
Another question worth asking is whether or not any of your ingredients are soluble in the bucket over time. It’s usually more of a problem with boron containing materials, but some feldspars can be subject to this as well. Solubles can affect glaze application if they cause additional gelling.
It doesn’t settle as in rock solid but there is a thin layer of material sitting along the bottom within 5minutes. I wonder if I have ruined the glaze batch by adding too much Epsom salts? It’s not overly thick at all…almost like single cream consistency. It seems that the 5 Tablespoons of saturated Epsom salts I added didn’t cause it to turn too thick/sludgy or make much difference to the consistency but still appears to have the very thick drip runs after a 3 second dip.
All the ingredients stay dissolved in the bucket if that’s what you mean by the last question? - sorry I’m a bit confused by this question.Thanks so much for your help
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1 hour ago, High Bridge Pottery said:
So even in your smaller trials the glaze is the same thickness and settles out quickly?
Can't see much in the recipe to make it thick. Been a long time since I used zinc but I think that can thicken glaze but probably not at 3%, 15% china clay shouldn't thicken it that much either and be pretty good at suspending the rest.
Yes it also settles out in the trial glaze batch. I’m also quite stumped as to why it has drip “flowing” marks. Perhaps it will be better if slightly thinner at a SG of 1.4?
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13 minutes ago, Hulk said:
Good idea to start with a test batch!
Did the Epsom salt addition make any difference at all?
My glazes, some require more Epsom salt (saturated) solution than others.
A few points in specific gravity can make a difference; I run as low as 1.41 (one glaze), high as 1.46...
...after an addition, stir, stir, wait, test, then give it some time before making another addition.How to measure the "gel" - when has enough Epsom salt been added?
See Tony Hansen's video clip:
Thixotropy and How to Gel a Ceramic Glaze (digitalfire.com)
...stir the glaze at a repeatable and reasonable speed, then watch as the revolving mass slows and comes to a stop.
I look for three to four turns before the entire mass slows to a stop, then "bounces back" just a little bit.Glaze that requires adjustments just keeps on spinning well past three or four turns, with currents of different speeds shearing against each other.
For pouring and dipping, slow and deliberate motion, particularly pouring out or lifting up.
A bit wetter glaze (lower specific gravity) allows more time to complete the glazing, but takes longer to dry.Hope that helps, check back for more suggestions from others, and please do update on how it goes...
I have added about 5 Tablespoons saturated Epsom solution to a 21litre batch and hadn’t made much difference to the drip marks but has increased the drying time. Doesn’t appear to be getting any thicker after adding Epsom solution and still spins for about 6 seconds or so. It is odd though because if I take about 1 litre in a small just and mix it up it stops after about 3seconds but in the large 21 Litre bucket it keeps spinning??? Which do I use ?
I have watched the video from Tony Hansen and added a tiny amount vinegar to a tester pot and this made no difference at all. If I get the SG down to about 1.36 then the drip marks seems to reduce but then won’t it be a deflocculate glaze if too much water is added?
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Hi all, having a bit of a hard time with glaze application.
Recipe:potash feldspar 33. talc 21. quartz 16. china clay 15. whiting 12. zinc oxide 3.
recipe is quite thick and tends to settle easily on bottom of bucket. I have upscale this recipe to 12 000g batch so is approx 21L in the bucket . S.G is 1.44. Added a bit of Epsom salts to help with the glaze settling. Issue is, the glaze seems to run quite a bit when applied to bisque ware. As it’s quite thick it sends to run slowly and leave really thick streaking marks. (Image attached). Not really sure whether to continue flocculating, but will this make it even more thicker??, or deflocculate, or add water which will start to take the SG below 1.4.
any thoughts greatly appreciated.
Kathryn
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On 12/10/2023 at 5:50 PM, Min said:
As long as the final segment is slowed down (as you are doing) then no, speeding up the second segment should't cause any issues. Have a look at the "slow glaze firing profiles" from L&L kilns, regardless of final cone reached the middle ramp goes at 400F / hr. (204.4C / hr).
A heads up though, when using a set temperature as your final cutoff point rather than a cone you will need to keep an eye on your results and or cones as your elements wear. Given that the kiln will need to fire longer to reach a set temperature the extra heatwork needs to be taken into account. If you look at the Orton cone chart you can see that for cone 8 (using self supporting cones) for the last 100C of rise using 15C/hr gives a top temperature of 1211C, at 60C/hr it raises to 1249C and at 150C/hr it needs to go to 1271C. So if you program in 60C/hr but the kiln can't actually keep up with that then the final heatwork will be greater. This is not a big deal if you are keeping watch on what your cones are telling you.
One other point re your pinholes, and the possibility it is being applied too thick, are you measuring the glaze specific gravity? Is your claybody a grogged one?
Thanks Min, all great tips and info. Yes I am measuring specific gravity - approx 1.45. Clay is slightly grogged. I think I will try make sure the glaze is not too thickly applied and see how I get on.
Bisque firing frustrations
in Studio Operations and Making Work
Posted
Yes they do have preloaded cone programmes so Im going to give that a go next.