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Min
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Posts posted by Min
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@Kelly in AK +1 about inside and outside profile and thickness.
@Griffithpotteryworks, stick a couple thumbtacks into the pot from the inside at the midway point plus near the bottom of the side wall then trim down until you reach them. Remove the tacks then smooth over the holes they made. It's a good way to get a feel for how much clay can be taken off. Tap the pots as you trim them so you can hear how the clay sounds as it gets thinner then after a few pots you won't need the tacks.
- Hulk, Jeff Longtin and Kelly in AK
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I know you said the pots were dried for several weeks and they were candled but when looking at the images this looks like a blowout from an air pocket that contained moisture within. This isn't the same as an air bubble.
My hunch is that when you were centering and opening up the mass of clay there was some clay pushed down that overlapped the existing clay and formed a pocket. If the clay contains a fair amount of ball clay or other fine particle material and was also heavily ribbed over this would exacerbate the problem of allowing the moisture to escape. Think about a fully enclosed form, yes we can fire them without them exploding or having blowouts but it takes far longer for them to reach a bone dry state right the way through the clay wall than the same form with an opening in it. No clue what the weather and humidity is like in Northwest Arkansas, perhaps it's a contributing factor, don't know.
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On 12/4/2023 at 8:57 AM, Griffithpotteryworks said:
two strange blow outs during a bisque firing
Thanks for posting the photo but I'm a bit confused as to what I'm looking at. It looks like there is glaze on the circular area?
Could you take another photo that shows the entire pot? Was there any relationship between where in the kiln the bowls were in regards to the spyhole(s)? Spyhole(s0 left open during firing and cooling? New clay, recycled clay?
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39 minutes ago, Griffithpotteryworks said:
working on loading pics
If you are having problems posting pictures try emailing them to yourself which will automatically reduce their size then try posting those ones.
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If you have a look at the Safety Data Sheet (SDS) you can get a rough idea of some of what is in the glaze. For Laguna's Tangerine Ice a snippet from the SDS shows this:
Doesn't include colourants and I think they have omitted whatever material is supplying boron but you can see from the first line there is a lithium material, this could well be spodumene. There is also silica plus calcium carbonate plus kaolin plus bentonite. From looking at the glaze plus looking at the components above I would hazard a guess this is going to be a microcrystalline glaze caused by a high level of calcium (ie a calcium matte or semi-matte) and that is what is causing the dappled look. I'm going to hazard another guess and think there is also titanium oxide in it also, perhaps from titanium dioxide or rutile. Is this glaze glossy if fast cooled and more opaque and dappled/mottled when slow cooled?
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55 minutes ago, Libba Adams said:
My question is whether I need to use the same slow cooling schedule as before, or whether it would make a difference to use a faster schedule if all I'm trying to achieve is fully melting the glaze at the rims of pots.
If any of the glazes needs a slow cool to get the desired look of the glaze then no, I would not use a faster schedule. If all the glazes are fine and look the same with the kiln just doing a free fall then yes it would be okay. You might find refiring them causes the glazes to be a bit overfired if going to cone 6 as they have already had some heatwork. If in doubt I would include one pot in the next firing and see what happens.
Bigger issue would be why the bottom shelf is underfiring. Is this a kiln with a single thermocouple in the middle of the kiln? If so then going forward pack less mass in the bottom of the kiln, ie taller pots on the bottom, more density (short pots and more shelves) in the middle of the kiln. If it's a 3 zone kiln then I'ld be looking at doing a tc offset for the bottom thermocouple.
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Laguna supplies many of the smaller clay suppliers with their spars. It's my understanding Laguna might not continue carrying the Mahavir spar in favour of carrying G200EU, this needs to be confirmed though. Thread on Custer situation here. https://community.ceramicartsdaily.org/topic/29747-custer-feldspar-again-new-chemistry-2021-data/
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19 minutes ago, fergusonjeff said:
Peter,
I may be reading it wrong, but I think the original poster was referring to using bone and shell as wadding rather than as posts. Shells work great for wadding during the firing, but within a few days turn to powder. I imagine bone would be similar, but maybe less structurally stable during the firing.
Jeff
That’s the way I read it too. In the link I posted Simon Levin wrote of a fellow woodfirer who used thin slices of cow bones wadding.
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Hi and welcome to the forum.
Bones won’t survive the heat of the kiln. (think cremation)
edit: I was rethinking what I wrote and looked up using bones for stilts. Came across the following article, turns out you can you bones. Link is behind a paywall but you can access 3 free articles a month.
https://ceramicartsnetwork.org/daily/article/Wadding-for-Wood-Firing
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Hi Roy and welcome to the forum.
Yes, I would recommend firing the underglaze onto the pot. Many underglazes remain matte when fired to bisque temperatures. Try a test tile with the same underglazes and fire that to see how they look.
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@getmorecaffeine, it would probably be a good idea to start a new thread on this, would make it easier to find in a search.
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Post some pictures of the inside, outside and faceplate. Plus if there are any kiln shelves and posts.
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No clue if it’s still current but there is a post in this thread from Clayart 2002 where he gives his phone number. http://www.potters.org/subject59787.htm
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Hi Gabriella, there is a section here on the forum where you could post the kiln you have for sale. Link here to it: https://community.ceramicartsdaily.org/forum/33-community-marketplace-–-buyselltradefree/ If Craigslist is active in your area you could try there too.
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You can inscribe it as soon as the wax is dry to the touch. Let the underglaze dry before wiping it back.
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New Zealand halloyiste is really white but it's expensive. Could always add some zircopax to your epk if you find it isn't white enough.
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Clay needs to be leatherhard, I would try sooner if it hasn't been crisp lines and see what happens. When I did it I waited until the sheen was gone, You are using a smooth claybody right?
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13 hours ago, Denice said:
so I need 50 lbs of custar
Custer is a potash spar, that means there is more potassium than sodium in the spar. Kona F-4 is a soda spar, it has more sodium than potassium.
I for sure would hold on to the Custer given the recent closure of the mine. Kona F-4 hasn't been available for a few years, its replacement is Minspar 200 which works as a 1:1 replacement for Kona F-4.
I tend to hold onto materials, never know when you will need something if trying out new recipes or if something becomes obsolete.
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Hi and welcome to the forum!
I've used Forbes wax resist with good success for this. What you don't want is a wax resist that is oil based (these are the ones that are difficult to wash out of brushes).
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Hi and welcome to the forum.
13 hours ago, Batuu said:I had been absolutely blown away by the use/waste of energy and materials.
For sure it takes a heck of a lot of practice while learning to work with clay, who decides when a piece merits turning it from a recyclable lump of clay into something permanent that isn't readily recyclable? Is there value in a piece of functional work that with more experience a beginning potter could make better? I would say yes. Should the beginner be encouraged to only fire their best work? That's a difficult question to answer and I don't think there is a right or wrong answer here, it depends on the situation. I would argue for a child to have something permanent, regardless of the quality, it can lead to a lifelong enjoyment of ceramics and a feeling of pride. Should an adult with less than stellar skills fire their work? In a perfect world the instructor would have the student make multiple pots and follow this with a lesson in constructive criticism then with the students okay a culling of "lesser" pots encouraged.
Are there lessons to be learned as we progress with our skills to be learned from looking back at early work? I think there are. I have made a lot of real clunkers while learning, it can take years to really see the flaws in design or workmanship.
13 hours ago, Batuu said:further material lectures being a complete rarity. Nevertheless people are motivated to produce masses of products, never having heard about things like vitrification, abrasion, hygiene, glaze mistakes, etc.
Perhaps this is a reflection of the studio environment. Are these classes set up as instructional classes with glaze theory etc or are they recreational classes? Hiring practice for the instructors set high enough?
13 hours ago, Batuu said:I am not talking about some single pieces people give to friends or keep for themselves. I am talking about a whole new movement that does not seem to be interested the slightest in learning before/while making, but putting LOTS of effort into creating Instagram reels and corporate identities surrounding slow making and sustainability.
This is a really good thought. I don't spend much time on social media but for sure when I do go there it seems there are a lot of people working the system like you describe. Like I said though, I don't spend a lot of time looking, perhaps the question could be do makers of quality pots use social media and if so how heavily do they rely on it? @Callie Beller Diesel and @GEP, thoughts on this?
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I don't know how the price compares to Brent but I like my Bailey wheel with the removable splash pan. (bumping this thread, hope to get more replies)
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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?
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Okay, so in a very simplified nutshell a glaze at any temperature will have 3 main components. Silica (think of this as the bones of a glaze), Alumina (think of this as the flesh of a glaze) and Flux(es) (think of this as the blood of a glaze). All glazes, regardless of cone or firing method, will be comprised of these components. Fluxes are almost always used in combination with other fluxes, ie a glaze will have more than one flux. Silica can be sourced in a glaze as silica and it's also in feldspars etc, a good source of alumina is kaolin or ball clay.
The higher the cone firing the less fluxes are needed, so by definition there will be room for more alumina and silica in higher firing glazes than lower firing ones. Sounds like your glaze is over-fluxed for the cone you are firing it too.
When you added silica to the WC554 glaze it "did the opposite" I'm guessing it went more gloss? I would hazard a guess this is because you altered the silica:alumina ratio. This can happen when you add silica to a high alumina matte formula. High alumina mattes are glazes where the ratio between the silica and alumina fall within a certain range, adding silica to it will move the glaze into the territory of a semi or gloss. (This works when there are sufficient fluxes to dissolve the extra silica)
What I would suggest doing would be to weigh out a sample amount of dry glaze, say 200 grams, then add both silica plus epk to it. The ratio of the two is important, for every 1 gram of epk you need to add 1.25 grams of silica. Start with adding 10 epk and 12.50 silica to the 200 grams base then mix/sieve and dip a test tile. Repeat adding 10 epk plus 12.50 silica twice more and repeating the test tiles. Fire those and see what happens, in theory it should help stiffen up the glaze and return it to less of a gloss. If it's still too glossy then try with just adding the epk and omit the silica. (or run this test at the same time) Between the 2 tests, one adding both silica plus epk and the other just adding epk I think there's a good chance of success.
If the colour is diluted too much by the silica/epk then address that by adding copper carbonate, have to see how the tests turn out before guesstimating how much of that to add. The purpose of these tests is to "dilute" the fluxes. Like I said this is a crapshoot as we don't have the recipe to work from but I think it's worth trying.
Tungsten Trimming Tools
in Studio Operations and Making Work
Posted
Recent post discussing tungsten trimming tool got me thinking of the cost of these as I'm finally ready to break down and buy one. I did some research and found there are a few suppliers who sell blanks in the shape of trimming tool heads commonly seen for sale by a few ceramic suppliers / artists. (link below) I read up on how to sharpen tungsten carbide and either a diamond wheel or a green silicon carbide grinding wheel can be used, along with diamond files for fine sharpening. (we have a green silicon carbide grinding wheel) Most places that sell the blanks are wholesale orders only but there are places that sell samples of one piece. One supplier below who sells sample blank pieces for $25- US each. I can see how to get the outside bevel ground down using a diamond or silicon carbide grinding wheel but not the inside bevel, maybe a diamond bit on a Dremel for the inside angle?
Anybody resharpen their own tungsten tools? Does that work well?
I know I can just go out and buy one (for a lot more money) but ....
Anybody done this? Thoughts?
https://ostoncarbide.en.made-in-china.com/product/SxoUhujFAVWA/China-Hard-Metal-Ceramic-Clay-Trimmer-Tungsten-Carbide-Pottery-Scraper.html