PeterH
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Posts posted by PeterH
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1 hour ago, Kelly in AK said:
Scarva, from what I see, doesn’t publish absorption numbers for this clay body. It’s a worthwhile test to do yourself.
https://digitalfire.com/glossary/clay+body+porosity
Clay Body Porosity
In ceramic testing this term generally refers to the pore space within a fired clay body. It is measured by weighing a specimen, boiling it in water, weighing it again, and calculating the increase in weight (thus it is also known by the term absorption). As ceramic clay bodies vitrify in a kiln they densify and shrink (thus reducing pore space). The % porosity of a body is thus an indicator of its degree of vitrification.https://digitalfire.com/test/shab
SHAB - Shrinkage/Absorption Test -
On 5/21/2024 at 10:07 PM, Callie Beller Diesel said:
So given that I have 2 options available for possibly heating some slip: a metal bowl in the test kiln or a plastic container in the microwave, which one is going to make my boss question my sanity the least? I’ll let you know.
Maybe a milk bottle full of reclaim in a bucket of hot water would be less obtrusive? And defendable as trying to confirm @Magnolia Mud Research's observations.
... with some sort of waterproof under-bucket heated mat as a potential permanent solution.
PS I'm bemused about the physics/chemistry behind the behaviour. For example you might expect any low temperature based changes to slow down settling not to stop it.
However Brownian motion may be relevant.
https://digitalfire.com/article/super-refined+terra+sigillata
The 20-hour settling time may seem arbitrary, but it's not. I am grateful to student Rob Williamson at U-Mass for helping to determine the ideal settling time. There are several forces at work in this deflocculated mix. The deflocculant introduces same electrical charges to particles in aqueous suspension, causing them to repel one another and stay in suspension longer. Also, there is ever-present atomic vibration which causes particles in liquids to naturally disperse. Working against these forces is gravity, causing particles to settle out. At 20 hours, in a deflocculated slip of the correct specific gravity, gravity has caused all the heavier particles to settle out, while atomic vibration and the repelling forces caused by deflocculation keep the finest particles (generally those less than one micron - 1/1000 of a mm) in suspension.PS
1) Viscosity might changing by a factor of 2 or so.
2) Electrical double layer effects can change with temperature.
https://tinyurl.com/2vxyrjxc
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In order to evaluate replies you will need to know what current you can draw from the socket. If it's the only socket on a 15A breaker I believe US "continuous load" regulations limit this to 12A.
It might be worth starting a new thread to solicit the experts views on reconciling you ambitions and the limitations of your house wiring.
PS I understand that if you regularly fire a kiln at its maximum rated temperature the life of the elements will be reduced considerably.
PS
Even on a dedicated connection both breaker size and house-wiring size are important eg
https://www.olympickilns.com/wp-content/uploads/2024/03/2023-Electric-Kilns-Operating-Manual-1.pdf
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A couple of previous threads.
... possibly defloculate
... mix well and possibly screen
... wash out sprayer as soon as you've finished
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3 hours ago, Babs said:
Well, can you show the interior? Looks like a Min glazing technique.:-)))
For those that haven't seen it:
- Rae Reich, Kelly in AK and Hulk
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I await the discussion with great interest.
PS
It's almost certainly irrelevant, but I'll mention an odd-ball method I once read about for reducing the adhesion between the casting and the mould.They were making a medical device that needed to be X-ray transparent, so the thin body was basically alumina and totally non-plastic. They found that mould release was more practicable if they first cast a very thin layer of paper fiber into the mould.
It was obviously a high-value item, so mould life may not have been an issue. I don't think that there was much detail in the mould either.
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4 hours ago, Bill Kielb said:
Ya probably already know this but worth mentioning I think. Breakers fail because they are old but also because they overheat. Here in the US the breakers you buy should not exceed 80% of the rating stamped on the breaker. For kilns which are considered continuous loads by code, per code they require a breaker at least 125% of the kiln full load and not more than 150%.
For a kiln that draws 40 amps, minimum breaker size if 50 amps (40X 1.25), maximum breaker size is 60 amps (40X1.5). I mention because electricians often get this wrong. The rule is there to prevent the breaker from overheating and failing prematurely. Often this is not common knowledge so I think worth passing along since you just experienced a worn out breaker on this kiln.
... and presumably the "house" wiring needs to be rated for the new breaker size. Which might be an issue for some retro-fitters.
- Rae Reich and Bill Kielb
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Some ideas on the causes & avoidance of problems in:
Microwave safe
https://community.ceramicartsdaily.org/forum/23-clay-and-glaze-chemistry/PS Pedantically in the USA:
... although I expect that -- like many stress tests -- this only implies safe at the point of test rather than lifelong safety. [Unless you re-test after representative "wear and tear" such as crazing and chips.]
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5 hours ago, Piedmont Pottery said:
I agree strongly. India ink enhanced crazing can be very dramatic and beautiful. If you or the gallery owner can't live with the result, the ink will burn off if you refire the piece.
If the crackle was pretty dense and it does re-craze it might be worth considering an "iron wire and golden thread" effect.
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1 hour ago, Graceadieu said:
also, I’m new to this community. Is there a “notification “ or “search topics” function?
At the top RHS of the green stripe near the top of the page.
BUT the inbuilt search only looks at "active" threads. The only way I know to search closed threads is via a normal search engine.
PS
Personally I use google with something like this
site:community.ceramicartsdaily.org aubergine
... which only gives 3 hits.BTW the site: directive works for google, but not for DuckDuckGo. No idea about other search engines.
The search site: community.ceramicartsdaily.org gas kiln gave "About 2,740 results" for me. Although the exact number probably depends on the vagaries of the internet.
Needless to say I usually only look at the first few hits (and other posts in the same thread). Frequently using their contents to refine the search terms - as I did when looking into manganese "violets".
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Maybe of slight help:
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16 hours ago, s6x said:
I read an instance where a glaze should not be used on a pot if that pot was glazed on the inside as well.?
I haven't seen that, and would be interested if you have a ref.
But I have seen occasional references to needing to let the pot dry sufficiently between glazing one surface and the other.
... this seems to be more of an issue with dipped glazes than painted ones.
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42 minutes ago, oldlady said:
the glaze used was made by the instructor, did i miss where it is actually a commercial glaze?
No, Min suggested switching to a commercial glaze used in an Amaco underglaze colour chart.
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20 hours ago, davidh4976 said:
Even with test pieces side-by-side in the kiln (one with GB, one without), the conversions that I have tried are coming out more blue than green even with the exact same amount of cobalt carbonate and rutile.
Any relevance?
https://digitalfire.com/material/gerstley+borate
... at the bottom of the page, discussing substituting Gillespie Borate for Gerstley Borate ...
Clearly, the Floating Blue itself is firing greener than usual. And the Gillespie Borate version is much bluer. You may be used to something in between these two. The green tones could likely be restored by a reduction in the cobalt and increase in the iron oxide.
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1 hour ago, ChrisC said:
Thats really interesting as I have another kiln that is 35amp and rated for a 40amp circuit, I'm not sure how thr rules differ in Australia though. I'll quiz my electrician.
I was interested to find this Australian article
https://sydneynorthshoreelectrician.com.au/electrical-service-panel-how-to-calculate-electrical-load-capacity/
... which contains these sentences
It is commonly recommended that the load never exceeds 80 per cent of the capacity of an electrical service panel.
and
The National Electric Code recommends that the overall capacity of the load does not exceed 80 per cent, ...Which suggest to me that there is no regulation demanding "over-rating" of breakers (at least in that region of Australia). But there are both informal and formal recommendations that this be done - apparently for both continuous and non-continuous loads.
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22 hours ago, HenryBurlingame said:
I actually have been thinking about exploring slow cooling as well as putting things in saggars to get reduction effects. I am sure I can figure out ways to get glazes I like in an electric kiln… just won’t be quite as straight forward as doing it in a gas kiln…
It would be nice if you started a thread on the topic in say 3-12 months indicating your successes and failures in this area.
PS A less well-known technique to achieve reduction. Which I think I've only seen mentioned in a 1932 paper on copper reds.
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2 hours ago, Kelly in AK said:
With slip (the added kaolin is not helping), underglaze, and glaze, you’re working on making four things play nice.
Re-reading Digitalfire the second paragraph seems relevant..
Glaze Shivering
https://www.digitalfire.com/trouble/glaze+shiveringShivering is the opposite of glaze crazing, the fired glaze is under compression and wants to flake off the body, especially at edges. However the route cause is a mismatch in the thermal expansions of body and glaze, thus the process of resolving it is similar as for crazing. It it much less common because glazes tend to have a higher thermal expansion than bodies and because they can tolerate being under compression much better than being under tension. Of course, if a glaze is under compression on the inside of a vessel, the body will be under tension and this can cause failure of the piece.
When the body-glaze interface is not well developed an overly compressed glaze will be able to release itself much more easily, especially on the edges of contours. This can be the case, not only with low fired ware, but where engobes or slips are being used under the glaze. If the engobe does not contain enough flux to firmly adhere it to the body and develop hardness, it will not be able to bond to the glaze well.
PS Time for some rim-shaped test-tiles?
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8 hours ago, HenryBurlingame said:
Starting to lean toward electric now holy cow
If you are leaning that way have you explored slow-cooling in an electric kiln? Which can have a dramatic effect on some glazes.
PS Some eye candy.
https://ceramicartsnetwork.org/daily/article/Super-Cool-Slow-Cooling-in-an-Electric-Kiln
https://cone6pots.ning.com/forum/topics/slow-cooling
https://ceramicartsnetwork.org/daily/article/Tips-for-Increasing-or-Decreasing-Crystallization-in-Glazes
... same glaze fired in a gas kiln: with the "natural" slow cooling of a gas kiln & with a "crash" cooling similar to that usually given by an electric kiln.
https://digitalfire.com/schedule/c6dhsc
https://digitalfire.com/picture/bestenazoh
https://digitalfire.com/picture/3348
A discussion on iron reds in this thread
http://ralpotterystudio.blogspot.com/2010/08/new-glaze-tests-710.html
... a fairly mixed bag, including
Previous firings of this glaze at cone 6 or less without slow cooling produced dark browns. This is one that really requires slow cooling to get the red appearance, but proves you can get red reds at cone 6.- Hulk and HenryBurlingame
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On 4/29/2024 at 11:26 PM, Mbrand27 said:
My problem is, this is a 17 amp kiln, and the 120V infinite relay they recommend
Idle thoughts while are are waiting for details of the kiln.
If it's a 120V 17A Paragon they seem thin on the ground, see P5 of ...
https://eadn-wc04-7751283.nxedge.io/wp-content/uploads/IM5-A-and-B-Paragon-Inst-Man-Jan2017.pdfPossibly relevant.
https://eadn-wc04-7751283.nxedge.io/wp-content/uploads/A-11-9B.pdf
https://www.theceramicshop.com/product/9663/paragon-a-11-9b-element-120v/What mains supply do you have, and is 240V available? (Series wired with a 240v infinite switch would halve the current.)
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3 hours ago, ChrisC said:
Thanks Peter, That is really handy. I'm in Australia and my supply is 240v - the one thing when looking at the drawings is when using V/R for Amps I dont get 40amps as per their drawing - Is there an example of how to calculate that ?
I calculate 240/17.3 + 240/(8.6+8.6) + 240/17.3 = 41.7 amps
I'm not familiar with kilns, but the difference between 40 & 41.7 could well be related to the fact that the resistance of the elements rises as they get hotter.
PS There are lots of mnemonic diagrams about if you need a reminder of the formulae.
https://duckduckgo.com/?q=voltage+current+resistance+triangle&t=ftsa&iax=images&ia=images -
17 hours ago, davidh4976 said:
When you open it up to measure element resistance, you also want to note how they are connected. Some may be connected in series and some in parallel. With that configuration information and element resistance, you can calculate the total current draw and therefore determine the required circuit size.
Purely as an example, you can find Paragon kiln diagrams at
https://corp.paragonweb.com/support/kiln-wiring-diagrams/There are three for the TNF233 (single/three phase and probably different controllers), showing differences in resistance and connectivity between elements.
e.g. https://eadn-wc04-7751283.nxedge.io/wp-content/uploads/Wtnf233.pdfBTW what is your mains supply?
https://en.wikipedia.org/wiki/Mains_electricity_by_country
Nominal voltage is 230/400 V, in practice 240/415 V is more commonly used.
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13 hours ago, LinR said:
This subject reminded me of seeing Carlton Ball in the late 70s or early 80s. He had made several kinds of horns which worked and looked fantastic. I wonder if anyone here remembers his work? Lin
A picture of one of Carlton's horns, and other peoples work (e.g. 4-headed drum, multi-chambered wind instruments, ...)
clay musical instruments
https://www.pinterest.com/baldaufa1/clay-musical-instruments/ -
12 hours ago, Neil Fallon said:
Does material in glaze have a shelf life?
https://ceramicartsnetwork.org/ceramic-recipes/recipe/Malcom-Davis-Carbon-Trap-Shino-143805#
If the glaze ingredients are (partially) soluble it can cause troubles.
1) Ingredients that dissolve in the water are likely to finish up absorbed in the clay body, rather than remaining at the surface and entering the glaze melt.
Maybe your recipe expected the soda ash to do this, but not the Nepheline Syenite ???
Expert opinions welcomed. <<<2) If the glaze slop is subject the thermal cycling partially soluble ingredients can cause strange effects.
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On 4/11/2024 at 4:52 PM, Denice said:
They would have dinner al fresco and listen to the gentle wind creating musical tones from the gourds.
A nice idea, which triggered this thought.
There may be some ideas on the use of gourd-size resonators in this book that could be implemented in ceramics.
change location and currency for some local prices
https://www.bookfinder.com/search/?full=on&ac=sl&st=sl&ref=bf_s2_a1_t1_1&qi=OAsKRPTKCBg9erQLq0pcohcePyM_1714219097_1:2689:6113... perhaps sometimes using mixed-media (e.g. the banjo-like instrument).
Wood ash glaze conundrum
in Clay and Glaze Chemistry
Posted
A thread testing the effect of sugar versus some other additives in a related context.