Gonepotty
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Posts posted by Gonepotty
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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.
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On 12/10/2023 at 4:19 PM, Hulk said:
My (limited) experience indicates that pinholes can (also) be caused by gasses expelled by the clay.
In that case, I don't know if dropping and holding a) slows the gassing/fizzing down, b) allows time for the particle to complete its decomposition, or c) combination of both.
Any road, the glaze would have to still be fluid enough at the hold temp to flow back together...Other factors that may be in play:
hotter and/or longer bisque fire, to burn out offending/gassy bits more thoroughly;
supply adequate oxygen during bisque and glaze fires, to burn out offending/gassy particles more thoroughly;
ramping up the bisque fire time for thicker wares, as it takes longer.Thanks very much
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On 12/10/2023 at 3:38 PM, Bill Kielb said:
Sorry did not read the whole thread above…. Of course you use cones! Just a thought, some glazes will pinhole and not heal well when fired hot. Counterintuitive, they do liquify more but don’t necessarily spread out and heal as one might think. Drop and hold is often an effective way to get these types of compositions to heal.
I also assume you are firing cone 8 because it matches your clay and glaze maturity requirements. If not, firing too hot can have its draw backs.Thanks Bill. Yes I am firing to cone 8
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5 hours ago, Min said:
Pinholes can have a number of causes, if it's an issue that you haven't been able to fix I would be looking at trying a drop and hold (soak) schedule as a first possible fix. To do a drop and hold let the kiln free fall in temp to approx 40C below top temp then hold there for 20 minutes then kiln off (if you don't do a slow cool). If the glaze is fairly stiff then yes for sure having it too thick could be the cause of the pinholes.
I also think you could try increasing your second ramp to about 175-200C per hour up to 1120C. It shouldn't have any effect on the pinholes and it will decrease your length of firing. It's the last 100C of the firing that is typically slowed down to 60C/hr.
Thanks Min, I’ll try fix the pin holes (potentially too thick and glaze recipe issue) first but the drop and hold sounds like next step if I can’t get ontop of the pineholes.
with regards to increasing the second ramp, is this likely to alter the appearance of any glazes or cause any blistering etc? I’m quite new to using my own programmes rather than using the standard presets of the skutt kiln.
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6 hours ago, Bill Kielb said:
just an observation
The 20 minute hold likely gets you to cone 7, not sure if that is what you are trying for. Do you use cones?Thanks Bill. I previously tried top temp of 1230oC and it overfired quite a bit fully bending cone 9. Yes I use witness cones and this schedule gives me a perfect cone 8
- Hulk and Bill Kielb
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2
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On 12/8/2023 at 6:23 PM, Min said:
I'ld call that cone 8. Do you do any sort of drop and hold/soak on the cool down? What is your rate of climb towards the end of the firing? Are the pinholes a new issue? Glaze recipe(s)?
Hi Min,
firing schedule (Celsius) is 1) 90o per hr until 300oC. 2) 115o per hr until 1080c 3) 60o per hr until 1220oc with a 20min hold. Pin holes could have been caused by a glaze too thickly applied
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1 hour ago, Jeff Longtin said:
Good Morning Kathryn,
fyi: typically the cones are set in the opposite of what you have done here. That way they can melt and not influence the neighboring cone. (So when 7 melts, there's no chance it will fall on 8, and affect it.) The sequence results in a shape that looks like the Sydney Opera House. (The first cone bent alot, the middle cone bent a bit, and the third cone just starting to bend.)
Digitalfire has a great page about these things. Pyrometric Cone (digitalfire.com)
While Orton suggests a specific angle at which the cones indicate specific temperatures I've found cone plaques, and what they tell you, to be more subjective. If your glazes look beautiful when fired to these temps than thats the bend you want to maintain. If your glazes seem overfired than you would want to lower the temperature a bit.
The other thing that cone packs help you understand is consistency. These two cone packs look fairly similar. Thats good, If they're two different firings or two different areas of the same firing it looks like you have a measure of consistency. So thats good.
I always look at the "guide" cone to decide if a kiln "overfired". If the guide cone has bent alot then its a definite overfire. If the guide cone has bent a little then its not a bad thing. It really depends upon what the glazes look like. Are you happy with the glazes?
Hi Jeff,
thanks for your reply and details. All noted:)
I’m not that happy with the firing, have experienced quite a few pinhole issues so wasn’t sure if the kiln got too hot and started creeping above cone 8 temperature.
1 hour ago, Jeff Longtin said: -
Hi everyone, wondering if you could help please. Im still learning how to interpret witness cones and not sure if these have overfired past cone 8?
(cones are from right to left :7,8,9 )
thanks so much,
kathryn
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7 hours ago, Kelly in AK said:
It’s a legitimate question. I have programmed every segment of both bisque and glaze firings so I could have a sense I knew what the kiln was doing and evaluate the pots based on that. It didn’t last long. I can see the schedules in the manual, I’ve got no reason to believe I can make the kiln work better than the people who designed it. I did give it a good, honest try.
Fewer button presses. Less to keep track of. Cone fire. 04. Speed (depends on how much of a hurry I’m in). Hold, if I’ve got some dodgy, gassy clay. Preheat is the revolutionary setting that took way too long for someone to come up with, no more explosions. Finally. That was the only real reason I used ramp/hold in the first place.
That said…it seems like your schedule ought to have gotten you there, so please pardon my smarty pants opinion. You’re using cones, you will definitely know what your kiln is doing.
I can be a simpleton. Celsius still eludes my grasp (not so much targets as rates, anymore). Try the cone fire mode though, i
Thanks
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10 hours ago, Bill Kielb said:
Just curious, since it is a Skutt with the touchscreen controller, why not use the cone fire programs rather than working with holds and various rates? Also - to get a particular Orton cone to fall it’s customary to set the last segment rate to that shown in the chart. Begin that rate 100c before the cone temp. If you follow Orton, just curious if anyone has explained how that chart is intended to work?
I have tried using the pre programmed bisque firing and had similar issues with cones not bending.
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It's a new kiln and only done 13 firings. (Skutt with touch screen controller).
Program is in celcius
Set 1 :80 degrees to 600
Set2: 100 degrees to 800
Set 3: 50 degrees to 1000 with 20min hold
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Hi all, wondering if anyone can help please. Bisque firing seems to not get to temp according to witness cones.
Firing to 990/1000 celcius. Cone packs 07, 06, 05.
Cone 07 only very minuscule bend- I mean hardly noticeable.
Top peep left out until 600 celcius and then bunged in.
No issues with glaze firing, reaching target temps perfectly and cones spot on.
This is very frustrating as I think the bisque must have undefined due to glazed pots with new pinhole issues...
Thanks for any tips/help
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1 hour ago, Pyewackette said:
I use 1/2" hardiebacker board for reclaim. So far I use the same board for wedging and reclaim because its the only one I have. I was intending to build a worktable to go with my new kiln but that all blew up last summer when it turned out we were going to be moving again. *sigh* The kiln now resides at a local pottery studio. It was apparently too late for me to cancel the order.
Anyway. I intended to try a double layer of the hardiebacker but since I didn't build the studio I didn't build the work table, but the single layer laid on my tile floor seems to work just fine for the little bit of reclaim I've been doing lately. You can tip the board up on its side and it dries out super duper fast. Unless you let it freeze/thaw repeatedly when wet it should last forever. Can't say if doubling the thickness would have made any real difference.
NOT DUROCK. Hardiebacker board. I use it for ware boards too.
Thanks:) never cake across these boards before...Will have a look!
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8 hours ago, Jeff Longtin said:
Interesting fact: once a plaster form has thoroughly dried, after the initial pouring, re wetting it, and allowing it to dry a second time, will completely open the pores contained within. This is probably inconvenient, regarding a wedging table surface, but it would enable you to take the utmost advantage of the plasters aborbing capabilities.
The degree to which the plaster slab no longer can absorb water is dependent upon the clay you use. If your clay contains soluble salts, sodium silicate or barium carbonate, for instance, it may slow down with age, but most likely your clay doesn't so you can expect many years of use.
As for drying a plaster form: heat is good but air movement is better. Too much heat, above 120 for instance, can start the breakdown process, too much air movement, has no bad impact at all. Put a fan on your plaster slabs and they should dry much sooner than simply letting the still air dry them.
Brilliant:) thanks so much!
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Can these be reused continuously or will they eventually stop absorbing the water from reclaim ? I have a few which I have made and wonder what do I do with these when they no longer fit for purpose? Also wondering if they should be thicker or thinner? Mine are currently 5cm deep and wonder if this is why they take sooo long to dry out I between reclaim batches.
Thanks:)
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Thank you so much for your help. I'm right at the very starting on mixing up glazes from scratch so have been thrown into the deep end of glaze chemistry which I am loving but equally lots to learn. Glazy.org has been amazing with recipes and community of potters all helping each other:)
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On 2/6/2022 at 11:24 PM, Min said:
I reformulated your recipe using Gillespie Borate. Instead of using a hypothetical analysis for the China clay I used Grolleg for both the reformulated recipe and in the original. Let me know if you use a different kaolin / china clay and I can redo it. I used the chem analysis from Glazy for the original recipe using Calcium Borate frit from the link @Magnolia Mud Research provided above. This looks okay on paper but if you try it please make sure and do a small test batch before using it on actual pots.
Linda Bloomfield ^6 Clear with Gillespie Borate - untested No dolomite needed, its getting enough magnesium from the Gillespie.
Potash Feldspar 22.2
Silica 24.4
Gillespie Borate 27.1
Grolleg Kaolin 18.2
Whiting 8.1
total 100
Screen shots of both the original and my version of it using Gillespie if you want to compare the chemistry.
thanks so much for your help. This is fantastic! I will test this out. Any pointers/youtube videos on how I could go about reformulating glazes as you have very kindly done? Im very new to creating glazes and this would be very useful.
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Potash feldspar 34
Quartz 23
Calcium borate frit 14
China clay 13
Whiting 11
Dolomite 5
Can get Gillespie borate....
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It was suggested I try low expansion frit or borax frit
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Hi all,
I have a Linda Bloomfield glaze book which with a shiny base recipe which calls for calcium borate frit.....this in no longer available in the UK. Wonder if you have any ideas of a substitution?
thanks!
Hi everyone, wondering if you could help please. Im still learning how to interpret witness cones and not sure if these have overfired past cone 8?
Glaze dripping
in Clay and Glaze Chemistry
Posted
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?