PeterH
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Posts posted by PeterH
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15 hours ago, Min said:
I looked up the Lavafleck and see that it has a firing range of 1200 C - 1270C. Clay is at its strongest when fired to maturity so if possible I would suggest raising the 1240C that you currently fire at. (and adjusting glazes as necessary)
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I found a potclays-clay-analysis.pdf file on the https://www.bathpotters.co.uk/ site.
https://www.bathpotters.co.uk/userfiles/file/potclays-clay-analysis.pdf
...which gives vitrification range 1250-1280 & firing range 1200-1280PS Finally found it on the Potclays site.
Click download file in the Clay Analyses box on
https://www.potclays.co.uk/Technical-Information -
On 1/24/2024 at 12:10 AM, s6x said:
I know there are glazes that will crackle, but I would like to have some serious, deep crackling, like in this piece, which I assume was achieved by adding slip at some point... but how do you do this in a manner that will make the slip seriously crack, but not fall off?
I like how the surface of the piece in the photo is red on the bottom, but the top crackling layer is white. Was this effect achieved by manually painting the cracks? or is it possible to apply a red glaze first, before a white slip is applied on top?
My first impression that it's not a normal crack pattern, which are often well described by
Hierarchical crack pattern as formed by successive domain divisions Pt 1
https://www.researchgate.net/publication/235540544_Hierarchical_crack_pattern_as_formed_by_successive_domain_divisions_I_Temporal_and_geometrical_hierarchy
Which seem to have a family resemblance to many crackle glazes, and this crackle slip
https://glazy.org/recipes/56903
... which isn't looking too like Aneta Regel's work to me.
Perhaps this is because there are "large" grains inside the shrinking "slip", causing both local "hot-spots" in the tension and impeding the free propogation of the crack within the mixture. -
On 1/22/2024 at 4:14 PM, Simon77 said:
Is it possible to slip cast in a waste mold?
If by waste mold you mean a sculptor's mold that cannot be removed from the casting without being destroyed ...
I think the answer has to be no, as the fragile casting would not survive any process that required the the mold to be destroyed to free it.It may be possible to make a reusable multi-part slip-casting mold from the original clay master. If this can be done without undercuts which would prevent freeing the casting from the mold.
>The thing is that i have a larger sculpture ...
... although large slip-filled molds are heavy and must retain their form during man-handling: e.g. use of natches for registration, holding things firmly together with straps, ...
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Is the video you mention the Ceramic Review ""masterclass"?
The accompanying article is at
https://www.ceramicreview.com/articles/material-beauty-2/PS A couple of quotes I found interesting.
https://tlmagazine.com/nomad-vibrant-colours-and-playfulness/
Stone (both presented and represented in her work) makes an important contribution to the materiality of Regel’s artistic practice. Her technique of mixing porcelain with gravel, placing stones into the clay, and subsequently allowing the clay to shrink and crack around the rock inside the kiln makes for a sensational sort of indeterminacy as the artwork rises to the challenge of forming and reforming itself.https://artsandculture.google.com/asset/raining-stones-aneta-regel/xAGlSpRuwPcv-g
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How did you get on?
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1 hour ago, Mardido said:
I heard a loud pop
I know zilch about wheels, but loud pops can be caused by an electrolytic capacitor blowing.
Can you post a picture of the component side of the circuit board?
- Hulk, Bill Kielb and Piedmont Pottery
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It's just possible that the work mentioned here has some relevance.
... but I've never been able to find more details. It doesn't seem to be mentioned here:
https://sure.sunderland.ac.uk/id/eprint/2824/1/NCECA_2012_Program.pdf
https://issuu.com/nceca/docs/2012journal -
Some discussion on the regs in https://community.screwfix.com/threads/rcd-protection-or-not.250927/
Including a comment on the (2005?) regs
It also confirms my suspicion that cookers are among the items least likely to be on a RCD, so it might be worth checking in your supply box. (Basically because UK cookers aren't usually on ring mains.)
If this is the case it -- and you have trouble getting the kiln fully dried out -- it could be worth considering a preheat on a RCD-less cooker feed.
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For what it's worth RCDs seem to trip at a higher current..
What is the difference between RCD and GFCI?
https://www.quora.com/What-is-the-difference-between-RCD-and-GFCI
They essentially are two names for the same device. In the UK and in Europe when English is used it is called an RCD (residual current device). In the US it is called a GFCI.
Now there are differences between US and Europe. In the US the triggering current is 5 mA. In Europe it is 30 mA. In the US they are electronic while in Europe they typically are electro-mechanical. In the US they often are in the sockets while in, Europe they are more commonly in the panel.More details in https://www.tlc-direct.co.uk/Technical/Distribution/RCD.htm
The British Standard requirements for RCDs (BS EN 61008) states that the RCD should operate between 50% and 100% of its rated tripping current. That is 15 mA and 30 mA for the 30 mA RCD. Most 30 mA RCDs operate at levels between 18 mA and 23 mA. -
A few examples from the net:
How to Make a Clay Cylinder - Ceramics Handbuilding for Beginners - YouTubeMaking a Clay Cylinder - YouTube
... and the three-part
How I hand build clay cylinders. Part 1 Pottery ceramics techniques - YouTube
How I handbuild clay cylinders Part 2. Removing the cylinder from the former. Handbuilt ceramics - YouTube
How I handbuild clay cylinders. Part 3 Attaching the base - YouTube
... where the cylinder is worked on while on a former
Note that a suitable diameter plastic pipe makes a good former being non-absorbent, smooth & strong.
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8 hours ago, neilestrick said:
Clay shrinks as it dries, especially from wet to leather hard. You have to get it off the form before it sets up too much. The wood will pull moisture from the clay and dry it out.
I find a picture often helps.
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Do you leave a hole in the egg to let steam out? If so this thread might be relevant.
But you don't want it to fall over in the kiln. 
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Perhaps relevant.
Flambe magic
John Britt investigates the appearance of mysterious crystals in the glaze slop.
http://ceramicstoday.glazy.org/articles/flambe_magic.html -
11 hours ago, C.Banks said:
couldn't find that page - thank you
I got the page, and it says that the demo is at
https://s3.amazonaws.com/nist-srd/ped_demo_5.1_setup_final.zipIf you have any further problems PM me with your email address and I'll try to email it to you.
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8 minutes ago, Min said:
@PeterH, using your train of thought...
If a high calcium matte glaze recipe was put into the EU calculator then the calcium in the recipe reduced until the EU calculator showed no excess calcium then in theory it would be a gloss when slow cooled. I'll try plunking MC6G High Calcium Semi-matte one into the EU calc. and see what happens to the flux ratio. I'll try it with both wollastonite and another recipe with CaCO3 and see where the flux ratio lands. (might be tomorrow before I get to it)
I assume that you intend to reduce both calcium & silicon, or is the amount of silicon involved a negligible fraction of that in the glaze..
I'd wondered if there was a trustworthy limit formula you could use, be interesting to see what it says.
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On 1/12/2024 at 12:34 AM, Min said:
Glad I'm not the only one thinking precipitates effect calculated flux ratios.
Have you tried to measure/estimate the UMF of the glaze matrix rather than that of the matrix+crystals? It seems a more logical number to use with the Skull chart.
For a high-calcium matt I understand that the crystals are calcium silicate, there are several to choose from but I'll assume 2CaO·SiO2.
So do a line blend of your existing glaze recipe and one with rather less 2CaO·SiO2 (or its precursors).
If you've straddled the just-no-precipitate recipe you have a good estimate of the matrix chemistry. If you didn't remove enough 2CaO·SiO2 you still have a closer bound on the matrix chemistry, and an idea how big the change in parameters such as flux-ratio are likely to be.
PS
- Obviously stick to a single cooling cycle.
- Probably best done converting the UMF to a "recipe" of oxides. Subtracting some 2CaO·SiO2 from the recipe. Then re-normalising (i.e. calculate the UMF of the new recipe).
- No need even to consider if/how you can make up that recipe from your original list of ingredients.
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+1 drying between wall-board.
In my limited tile-making efforts I also turned the slab+boards over from time.Re the use of silica sand, I found this a powerful analogy.
PS I was taught that non-optimum rolling can make the slab more likely to warp: frequent turning & unsticking from the rolling surface, gradual reduction in thickness, rolling in multiple directions, don't let any thickness guides constrain the slab's edges, ....
- Bill Kielb, Rae Reich and Ben xyz
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3 hours ago, akilpots said:
there is a new edition out which is much cheaper.
Now lots available at £24 over here
https://tinyurl.com/2p4k2jst -
Can anybody explain the apparently white areas around the red line and dots
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22 minutes ago, Suresh Sundaram said:
I’m trying to create the look that’s on the cover of Robin Hopper’s Making Marks book
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> I was looking for the trial version of the NIST? phase diagram software ...
Just to point out that there is a time-dimension to phase transforms that phase-diagrams don't capture.
A physicist might say that they are "thermodynamically correct", and only show what phase has the lowest energy under the given conditions. Saying nothing about how long the change of phase will take.
AFAIK it's rarely of practical significance, although I suppose it's relevant when the timing/temperature of the firing becomes important: e.g slow-cooling microcrystalline glazes, nursing macro-crystalline glazes.
The effect is spectacularly evident in the phase diagram of carbon.
Normal temperature and pressure is about 1 bar & 300K. So every diamond you have seen is about 1,000 bar away from a point where it is "stable" ... and not much closer during the geological time where it was in fairly-near-the-surface rocks.
PS
https://www.whiteflash.com/diamond-education/diamonds-how-do-they-form/
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6 hours ago, GEP said:
Unity formulas, flux ratios, boron charts are all useful guidelines, but glaze chemistry has far more variables than us mere humans can test. No substitute for first hand experience. “Melt and see” is still an indispensable mindset.
Hard to argue with that, but I would suggest that they can help reduce the number of tests you need to make.
For glazes that phase-separate (e.g. many mattes) the UML formula will not accurately reflect the composition of the different phases. Which raises issues of interpretation and limit setting.
- Min and Kelly in AK
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It looks like this URL may show both sides of one of the 3 parts of 183F
But you don't want it to fall over in the kiln. 
Strange blow outs during bisque fire
in Clay and Glaze Chemistry
Posted
Re: memory in clay, just remembered this example.
Control of desiccation crack pattern using memory effect of clay paste
https://www.gruppofrattura.it/ocs/index.php/esis/ECF18/paper/viewFile/6064/1949