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Min
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Posts posted by Min
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26 minutes ago, GEP said:
The one my supplier is carrying is a Laguna product, and described as “Apparently the same as original Cornwall Stone but we recommend testing.” I am assuming this is the same one as Zamek’s analysis, but could be wrong.
If your supplier carries other Laguna products then it could well be but not for certain. If you could confirm this that could help. I'll have a go at running the recipe with that analysis and tweaking it to match as close as I can to the original.
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It's the grinding down of the blank going around the curves that I'm wondering about. I think it would be a lot more accurate if I had a jig I could clamp the blank to before grinding it, would help with angle too. There are also ones on aliexpress but I wonder about the quality of those. Hsin-Chuen Lin sells some also, they are all pretty close or the same shape. Makes me question if they are all getting the blanks then sharpening and finishing them.
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Is the Cornwall analysis from Ceramics Technical 2011 by Jeff Zamek? If so is that the formula from your supplier? Also, which talc do you have?
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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?
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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).
Custer feldspar... again... new chemistry 2021 data
in Clay and Glaze Chemistry
Posted
Three recipes below, original in the first one using Amtalc since a specific one wasn't specified. Second recipe shows what the formula would look like just doing a direct substitute of Cornwall Stone for the G200 and Fabi talc for the Amtalc. Third recipe is one where the oxides are as balanced as I can get them without adding another material.
Only change to formula in recipe 3 is potassium and sodium amounts are different when looked at separately but equivalent when looked at when the two oxides are combined. (KnaO figure) Given you are testing this for your liner I don't think this will make a difference.
Main difference is far more Cornwall is needed to supply the sodium and potassium than the G200 supplied. This extra Cornwall bumped the overall silica up so that needed to be reduced by subtracting silica. Same for alumina hence the small drop in EPK. Other oxides just needed minor tweaking.
Silica to alumina ratio is the same in 3rd version, COE is pretty close, this will be a minor fraction of a decimal difference, not significant.
I left the total for recipe 3 at 99.30 to keep the material amounts in whole numbers or just going into the tenths.
If you try this please just do a small test amount first, what looks good on paper doesn't always translate to the pot.