PeterH
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Posts posted by PeterH
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There's a brief thread on a Ceradel Socor kiln at
Yours should have a plate on it giving some important details. It might look something like this
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8 hours ago, Kelly in AK said:
I also see bubbly lava glazes use SiC for the effect. Maybe it could be useful in that way too.
Perhaps it's worth glancing at this, which looks at the effects of different SiC mesh sizes in lava glazes.
Testing Silicon Carbide Grits in Cone 6 Lava / Crater Glazes
https://www.thestudiomanager.com/posts/testing-silicon-carbide-grits-in-cone-6-lava-glaze
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2 hours ago, davidt said:
If there's a way to get in touch with PDWhite I would love to message him
Back up to his posting on this thread, and click on the big P.
Then click on the Message icon, and you are messaging him -- by email so he doesn't even have to access the forum to see it.
... keep an eye on the
icon at the top of the forum page to catch any personal messages addressed to you (it changes colour).
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18 hours ago, Wayne2 said:
One other thing; there is apparently confusion on the length of time used for these firings. I have been told a longer firing for a lower temperature is what one should expect when I questioned those firing times. That is counter intuitive to my expectations, as I would expect it should take less time to reach a lower temperature. I also tend to think Insight’s numbers should be closer to the time for firing if the kiln was working properly and the elements in good shape.
Are you sure that this isn't an indirect reference to heat-work? Perhaps in the context of unachievable ramp speeds.
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5 hours ago, ThruTraffic said:
How do I get clay like this without shipping it from Japan
These seem to be "wild" North Carolina clays (singly or as mixtures?). I've no idea if/where they might be bought, or how they might be approximated from commercial clays. Jeff makes a good point: if you are approximating the look of these clays then stains could simplify the process, especially if you wanted a palette of colours.
From Wild Clay: The Story of NC Clay https://www.woodfirenc.com/wild-clay
Sorry about the text size.
Also see
https://bandanapottery.com/materialsOur main clay body…
Our main clay body is mostly (75%) comprised of a mixture of two clays from our area: A coarse, red clay that is near our home in the higher mountains, and a more plastic grey clay that settled near a creek bed further down the mountain. We mix these wild clays into a slip and pour them through a screen into a large feed tank. The screening process is one of the first aesthetic and expressive decisions we make- the size of the screen determines the final landscape of particles in the clay beneath our slips and glazes. While dark in color, both these clays are so refractory in their pure state that we still need to add feldspar to the body to make it vitrify and hold water at stoneware temperatures. We also found that we need to add small amounts of ball clay, sand, and silica to our clay body to be durable and make the glazes fit. This brings up an important and interesting question- how much do we tame a clay to meet our functional expectations, and how much do we adapt and learn from the beautiful (and limiting) qualities that drew us to the wild clay in the first place?
PS Re Joseph's mention of Grogeewemee 10, here is a picture
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5 hours ago, ThruTraffic said:
How do I get clay like this without shipping it from Japan
These seem to be "wild" North Carolina clays (singly or as mixtures?). I've no idea if/where they might be bought, or how they might be approximated from commercial clays. Jeff makes a good point: if you are approximating the look of these clays then stains could simplify the process, especially if you wanted a palette of colours.
From Wild Clay: The Story of NC Clay https://www.woodfirenc.com/wild-clay
Sorry about the text size.Also see
https://bandanapottery.com/materialsOur main clay body…
Our main clay body is mostly (75%) comprised of a mixture of two clays from our area: A coarse, red clay that is near our home in the higher mountains, and a more plastic grey clay that settled near a creek bed further down the mountain. We mix these wild clays into a slip and pour them through a screen into a large feed tank. The screening process is one of the first aesthetic and expressive decisions we make- the size of the screen determines the final landscape of particles in the clay beneath our slips and glazes. While dark in color, both these clays are so refractory in their pure state that we still need to add feldspar to the body to make it vitrify and hold water at stoneware temperatures. We also found that we need to add small amounts of ball clay, sand, and silica to our clay body to be durable and make the glazes fit. This brings up an important and interesting question- how much do we tame a clay to meet our functional expectations, and how much do we adapt and learn from the beautiful (and limiting) qualities that drew us to the wild clay in the first place?
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10 hours ago, oldlady said:
dumb question, can plaster be dried out sufficiently to work again if it is heated to remove water?
Personally I doubt it's practical, but this at least tells you not to overheat it (see the last sentence in the quote).
Might be worth a try in a domestic oven.
https://en.wikipedia.org/wiki/PlasterChemistry
Gypsum plaster, gypsum powder, or plaster of Paris, is produced by heating gypsum to about 120–180 °C (248–356 °F) in a kiln:[18][13]
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CaSO 4 ⋅ 2 H 2 O ⟶ heat CaSO 4 ⋅ 1 2 H 2 O + 1 1 2 H 2 O ↑ {\displaystyle {\ce {CaSO4.2H2O {\overset {heat}{{}->{}}}{CaSO4.1/2H2O}+ 1\!1/2 H2O ^}}}
(released as steam).
Plaster of Paris has a remarkable property of setting into a hard mass on wetting with water.
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CaSO4⋅12H2O+112H2O⟶CaSO4⋅2H2O{\displaystyle {\ce {CaSO4.1/2H2O + 1 1/2H2O -> CaSO4.2H2O}}}
Plaster of Paris is stored in moisture-proof containers, because the presence of moisture can cause slow setting of plaster of Paris by bringing about its hydration, which will make it useless after some time.[19]
When the dry plaster powder is mixed with water, it rehydrates over time into gypsum. The setting of plaster slurry starts about 10 minutes after mixing and is complete in about 45 minutes. The setting of plaster of Paris is accompanied by a slight expansion of volume. It is used in making casts for statues, toys, and more.[19] The initial matrix consists mostly of orthorhombic crystals: the kinetic product. Over the next 72 hours, the rhombic crystals give way to an interlocking mass of monoclinic crystal needles, and the plaster increases in hardness and strength.[20] If plaster or gypsum is heated to between 130 °C (266 °F) and 180 °C (350°F), hemihydrate is formed, which will also re-form as gypsum if mixed with water.[21][22]
On heating to 180 °C (350°F), the nearly water-free form, called γ-anhydrite (CaSO4·nH2O where n = 0 to 0.05) is produced. γ-Anhydrite reacts slowly with water to return to the dihydrate state, a property exploited in some commercial desiccants. On heating above 250 °C (480°F), the completely anhydrous form called β-anhydrite or dead burned plaster is formed.[19][22]
- Jeff Longtin and Chilly
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3 hours ago, Magnolia Mud Research said:
Regarding @PeterH question: yes. long ago I began using a water spray of sodium carbonate as a means of controlling the fired effect of surfaces.
I ran out of sodium carbonate but had baking soda in the cupboard and used it instead; saved a trip to the store and the results were equivalent. I have been using baking soda more often as it is less damaging to my skin and is available at the grocery store near home.We seem to be talking at cross purposes. I was commenting on the use of sodium carbonate/bicarbonate for adjusting the rheology of a clay slip. While you seem to be adding sodium carbonate/bicarbonate to the surface of a pot then heating it: decomposing them to sodium oxide which eventually forms part of a "salt glaze".
Min (with a like from Callie) commented on another thread
How was your soda ash stored? If not kept sealed up in an air tight container it will change from sodium carbonate into sodium bicarbonate, which is a flocculant.
... and I was happy to take her/their word for it.
PS
This point has since amplified by quoting from http://www.marjonceramics.com/pages/Tips/slipmaking.htm
Soda ash works to dissolve lignite in clay.
... I've no idea of the details of this mechanism, which sounds more complex than the simple addition of Na+ & CO3-- ions to the liquid. I've only got as far as https://patents.google.com/patent/US3325537A/en
The humic acid content of lignite may be solubilized by treatment with alkalies, such as sodium hydroxide and sodium carbonate.
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42 minutes ago, Magnolia Mud Research said:
no need to "bake" the bicarb, just add more of the bicarb to equal the amount of sodium that you want to have in the mixture.
LT
Are you sure?
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8 hours ago, moonari said:
I’ve searched long and wide to find an answer to this question but I can’t seem to verify any actual written information regarding this topic.
You may be interested in (but not concerned about):
Flambé Magic
http://ceramicstoday.glazy.org/articles/flambe_magic.html
John Britt investigates the appearance of mysterious crystals in the glaze slop.
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43 minutes ago, njabeid said:
That's interesting!! I guess I need about 50 years to wrap my head around all this glaze chemistry stuff.
You may find this of interest
How to Increase or Reduce Crazing in a Glaze
How to Adjust Crackle Without Changing the Overall Appearance of the Glaze
https://ceramicartsnetwork.org/daily/article/How-to-Increase-or-Reduce-Crazing-in-a-Glaze -
I find terra sigillata a confusing term, which is also often unrewarding to use in searches. Some of the issues are described in
Terra sigillata https://en.wikipedia.org/wiki/Terra_sigillata
The introduction is especially relevant, and I include the first paragraph of it.
Terra sigillata is a term with at least three distinct meanings: as a description of medieval medicinal earth; in archaeology, as a general term for some of the fine red Ancient Roman pottery with glossy surface slips made in specific areas of the Roman Empire; and more recently, as a description of a contemporary studio pottery technique supposedly inspired by ancient pottery. Usually roughly translated as 'sealed earth', the meaning of 'terra sigillata' is 'clay bearing little images' (Latin sigilla), not 'clay with a sealed (impervious) surface'. The archaeological term is applied, however, to plain-surfaced pots as well as those decorated with figures in relief. -
On 12/12/2022 at 12:50 PM, ThruTraffic said:
If I understand correctly the Romans and Greeks didn't have/use a deflocculant in their recipes and were still able to achieve a gloss finish after firing.
After some searching I found this paper. Which contains some though-provoking facts and ideas.
Recovery and Revival of Attic Vase Decoration Techniques
What can they offer archaeological research ?
https://tinyurl.com/yecn6xnf
Of course the firing (and final effect) of this "black gloss" is different from that of t-sig, but they both start by forming a "colloidal slip" (with or without the use of a deflocculant).
p114 Gives the results of X-ray analysis of historic samples and modern "reproductions"
- This clearly shows that the originals didn't use phosphorous-based deflocculants (many reproductions used calgol).
- The "glaze" contains much lower calcium levels than the body.118 It is pointed out that
- The absence of phosphorous in the glaze implies that plant-ash deflocculants weren't used.
- Although not conclusive the potassium levels suggest that potash defloculants weren't used either.p119 Looking for a deflocculant-free method of producing the "colloidal slip".
- Using a low-calcium clay (similar to that used in antiquity) they found that they could get acceptable (deflocculated?) results a pH>8.7 and >15°C.
- Using the same clay pre-soaked for six months they got similar (not-deflocculated?) results at pH~7 and >15°C.
... this suggests that slip production was a seasonal process, probably during the warmer spring to autumn.
... assisted by over-winter soaking of the clay.The difference in calcium content between different clays is shown in fig2
PS I couldn't help speculating:
1. That the need for low-calcium clay was because that any soluble calcium compounds would act as
deflocculants. After all soluble calcium and magnesium compounds are used adeflocculants for glaze slips.2. Historically they may have found suitable candidate clays simply by paddling round the local clay-pits in late spring, looking for signs of spontaneous colloidal dispersion. Those wishing to find suitable modern commercial clays may need to look at them after a 6-months soak.
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On 12/23/2022 at 4:11 AM, Hulk said:
Hi Ceramics.np.04,
Above I'm disagreeing with PeterH, looks like your kiln is rated Cone 10 (or more), not Cone 6.
I should have been more specific.
A Cone 10 kiln element set should last a good long while when used to fire to cone 5/6.
I'm just saying it looks like a Cone 10 (or more) rated kiln.Apologies to all, a real senior moment.
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On 12/20/2022 at 6:57 AM, Tina01 said:
hunting/making clay is still in progress. as the last formula didn't work (infact it couldn't be tested as it had a horrible smell, something like fetid swamp rotten eggs after 5 days). Most likely because my bentonite keeps molding, no matter how many times I remove the mold layer from the top. So I finally mixed all the different clays I had and still working on dry powders to find a solution.
You could prevent the mould by adding a biocide. Short lived ones (that require topping up) are hydrogen peroxide and bleach (but bleach may be hard on the hands). A long-lived one is copper carbonate.
The Best Way to Eliminate Odor from a Stinky Ceramic Slop or Glaze Bucket
- Try to make sure that your waste doesn't get near any aquatic life, especially if you use a long-lived biocide.
- I could understand your "wild" clay going mouldy if it has lots of organics in it, but am surprised that shop-bought bentonite does.
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On 12/18/2022 at 12:56 PM, Ceramics.np.04 said:
it took so long for the final section of the firing to reach the desired temperature (1240°C/2264°F)
Thinks for posting the kiln plate. I hope that the experts will chime in, but I suspect that the max temperature of 1300C means that the element life - when firing to your desired temperature -- is likely to be quite short.
For example see the first answer in
PS I'm not certain if the figure of 50 firings includes the lower-temperature bisque firings.
- Ceramics.np.04 and Pres
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9 hours ago, Ceramics.np.04 said:
I'm aiming for a cone six but I still find the cone thing a bit confusing.
You may find this of interest, especially the sections What is Heatwork? and Put Witness Cones in Every Firing.
Temperature vs Heatwork – Why We Use Witness Cones
https://suemcleodceramics.com/do-you-put-witness-cones-in-every-firing/- Hulk and Ceramics.np.04
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1 hour ago, Ceramics.np.04 said:
Which leads me to my next issue: I don't think the manufacturers of my kiln exist anymore and no one seems to have heard of them anyway.
I don't know the best place in the UK to get elements, but some of them will probably try to reproduce elements for kilns from defunct manufacturers.
For example:
Kiln Elements, Repair, Servicing and Support
https://www.potterycrafts.co.uk/Products/kiln-elements-servicingCan you post the information from the plate here as well.
PS The plate probably looks something like this, partially printed and partially stamped.
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9 hours ago, Callie Beller Diesel said:
Since your elements are likely worn, you can still continue, but definitely include the cone packs this time, and make sure you’re checking the firing every 15 minutes for the last 2 hours or so. You want to be able to turn the kiln off yourself once the cones fall. If you fire overnight to avoid peak electricity rates, maybe start it about 2-3 hours later than you would normally, so you’re awake for the end.
18 hours ago, Hulk said:*be sure to wear kiln glasses against the harmful rays and any flying bits!
Both seem very sound advice (while the elements are worn).
19 hours ago, Ceramics.np.04 said:I stupidly decided to make all my christmas presents this year and, after the disaster of the last firing, I'm scared to do my final glazing with the crazy winter weather.
So does this mean waiting for appropriate safety glasses? Are we talking about welders glasses for IR & UV protection?
In the Studio: Eye Health for Potters https://tinyurl.com/3tcnc8tpPS Or -- in the absence of goggles -- could you measure the rate of temperature rise towards the end and stop the kiln closer to the right heat-work. Although you only have figures for 15C/h, 60C/h & 150C/h. BTW -- assuming you have a controller -- what is the rate of your last ramp?
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19 minutes ago, Ceramics.np.04 said:
I don't really know what I'm talking about but is it possible that because it took so long for the final section of the firing to reach the desired temperature (1240°C/2264°F) that it was too hot for too long?
A cone temperature chart confirms that this is a real effect. A cone number relates to an amount of heat-work and the maximum temperature needed to achieve this depends on how fast the kiln is heating towards the end of the firing.
https://www.overglazes.com/PDF/Orton-Cone-Chart-C.pdf
Did you previously fire by observing the cone drop or just use it as record of the firing?
- Chilly, Rae Reich and Ceramics.np.04
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7 hours ago, Juxtaposie Jen said:
My husband uses some really strong magnets that he can turn on and off with the handle.
I haven't heard of this before, do you have a trade-name for them?
This explains a/the mechanism, and may be a starting point for some DIY-er .
How to Build an ON/OFF Switch for a Permanent Magnet
https://interestingengineering.com/video/build-on-off-switch-for-permanent-magnetThe ones I saw on the net looked expensive, and possibly overpowered for the application.
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Possibly the right wiring diagram, but too blurred for me to read
https://eadn-wc04-7751283.nxedge.io/wp-content/uploads/W-EA-820-8-Control-Panel.pdHasfIt looks like the lower elements are fed by a power relay, are we certain that it isn't suck? (It might still click.)
icon at the top of the forum page to catch any personal messages addressed to you (it changes colour).
at's a lot.
How to diagnose a failed timer
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What position is your 3-position rocker switch in?