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Min
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Posts posted by Min
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That's interesting Kelly that you found adding Veegum works for you. Just curious, have you ever tried adding vinegar?
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It sounds like the problems you are having are from the same reasons blue / marine / quick clay causes mudslides. From the little I understand of it salts are responsible for the liquefaction of the clay, on a lesser scale this sounds like what is happening with it being easily collapsed while throwing and then the trimming issues. I don't think it's particle size, I think it to do with cations. Perhaps @glazenerd has a fix for this? Altering the charge on the particles maybe?
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I think you must be a lot tidier than me Tom. I've always got kiln shelves, bisque ware, posts, duster, a small table for loading pots from and other stuff with my kilns. I did have the kilns in an enclosed deck space for many years, carrying pots back and forth from my workroom, one trip to bisque then carried to glazing area then back again to glaze fire then back to finishing and storage area. It was a royal pain. Also if you have neighbours that are a bit fussy having it in plain sight can also cause problems.
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1 hour ago, Simon Heath said:
Thank you, yes, ultimately this is how I would like to do it, but the fit on the last few I've thrown has been too snug to do this. I think this is how I will have to do it going forward.
S.
If you want a "cheat" to help stop them sticking together during firing there is a workaround. Use a different clay, ideally a cone 10 body, and fire a holder for the lids. Make it like the shape below with the straight tiny wall at the top only about 1/2cm high, since this lid holder will be reused make it from clay that can take multiple firings without bloating etc. Raku clay or a cone 10 stoneware are good choices. Bisque it then use that to fire the lids on instead of with the crock part.
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Sounds like it could be Norwegian quick clay.
Moving this thread over to chem section.
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Going forward if you want to glaze the rim of the lid you can wax the rim of the water crock plus the area under the top of the lid and fire them together. When I do this I also wax a little ways down the tube of the lid. Have to have a really well fitting lid to do this the parts don't fuse together when glaze firing, tapering the tube part helps with this. Image below is from this article by Sumi von Dassow , she glazes them the same way you did, I added the red arrows to show an alternate way to wax and fire them.
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Salted butter or unsalted? Makes a difference in how fast it turns.
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Hi and welcome to the forum!
From a quick Google search it looks like you would be opening yourself to being sued if there was an issue with fire or shock. Link below from a company in California explaining the codes etc.
https://insights.regencylighting.com/ul-listed-or-etl-listed
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2 hours ago, Lucia Matos said:
Hi Pye,
Which pugmill did you decide to get? And how do you feel about it a year later? I have some wrists issues and want to be able to do this for hopefully many years, so I am considering buying a pugmill. Thank you!
Lucia
@Lucia Matos, Pye hasn't been on the forum since April 04 so it might be best to send her a pm just in case she doesn't see your question. She will get an email letting her know about your pm and question. (just click on her name then the little envelope at the top of the page that comes up then follow the prompts)
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Recently I started using pieces of a painters plastic drop sheet to cover pots as I had misplaced the roll of a different brand of plastic sheeting I had been using for years. There is a marked difference in the drying rate between the two types of plastic. It got me wondering about why this was happening.
Turns out there are at least 3 types of plastic sheeting that are broadly available and they have measurable differences in water vapour permeability. Low density polyethylene (LDPE), polyvinyl chloride (PVC) and polyvinylidene chloride (PVdC). I don't know what the original plastic sheeting I was using was made from or the brand, it's a large roll that I've been using for many years. The painters plastic drop sheet I just started using is this one. My hunch is that it's the type of plastic that is making the noticeable difference. Going forward I'm going to experiment further, pots I want to dry slower will get the drop sheet plastic and for ones I want to dry quicker my original roll of plastic. I should add all the pots were covered in my usual manner.
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CMC can also be mixed up so it's very concentrated. This is how I have been using it lately for a glaze really high in nepheline syenite that I brush on. I get the specific gravity where I want it then use an immersion / stick blender to whiz in about 10ml of the CMC concentrate to about 500 ml of glaze. I brush some on a scrap of bisque, if the brush drags then I whiz in another 10ml and keep going until the glaze is brushable. (CMC 33.5 Water 500 pinch of copper carb)
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10 minutes ago, Bill Kielb said:
Just asking, these have been fired several times and if yes to what temperature? Also curious about scraping off the lid. Did you kiln wash the underside of your lid?
I'm guessing "... ild ..." is old not lid?
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I developed my porcelain cone 6 slipcasting body then made a plastic version of it for pulling handles. I attached the handles to the cast mugs as soon as the mug bodies were able to be handled (no pun intended). I had pulled and formed the handles and allowed them to dry as much as possible but still be flexible enough to join to the cast bodies. My logic was to minimize the shrinkage difference between the cast body and the pulled handle. Just about every handle still shrank so much more than the body that the handles had serious cracks at the joins. Given that this is just one experience it might not be indicative of what is typical but given that a plastic body is going to shrink more than a non-plastic (casting) body my hunch is it could very well be the norm.
If you were attaching sprigs or other non load bearing attachments then perhaps it has a better chance of working.
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I compared your original Gerstley Borate recipe with nepheline syenite to ones with Solargil FR8 frit and the Ceradel 1254 frit then tried to come up with something as close as possible using what you have available. Roadblock I ran into was getting the silica and alumina as low in the fritted formulas as the original Gerstley Borate recipe.
I found a blend of the two frits, FR8 and C 1254, got the boron (melter) okay but the silica and alumina are a fair bit higher. I could take the kaolin out of the recipe to lower the silica and alumina but then it will be back to sinking like a stone in the bucket so I kept it in. This means it might not melt quite as well but if you are testing glazes it might be worth a try. Other thing to try would be to fire a bit hotter if it appears not quite melted enough.
I also included what the chem looks like if you use just FR8 or C1254 at 90% with kaolin at 10%. I find the format and colours of the glaze calc program I use very jarring, these are not easy to look at. Also, what looks okay on paper doesn't always work in reality so if you try the blended version please just test a small amount first.
- Hulk, Bill Kielb and Lilya
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10 hours ago, Callie Beller Diesel said:
Usually a glaze that heavily crazed will cause a pot to weep if the clay you’re using isn’t fully mature at the cone you’re firing to
@Julia8989, just going off on a little tangent here and adding to thought to Callie's post. Terms such as "mature" can be open to interpretation. Without trying to overwhelm a new potter with verbiage, in order for functional pots not too weep or leak, especially with a crazed glaze such as the one in your image, the clay would ideally need to have an absorption figure of less than approx 1.5% This means that the clay will absorb less than that amount of water when put through some tests to measure how much water the clay soaks up. Maturity can be a confusing term. With ceramics it generally means the point at which a claybody is as strong and dense as it will get without being over-fired and suffering from warping, bloating, brittleness and some other faults. For example, earthenware when fired to maturity can have an absorption rate well over 10% while porcelains get down to 0% and stonewares in between those two amounts. If you do try a heavily crazed glaze such as in your image its more important than ever to check the absorption of the clay you will be using at the firing cone you will be firing it to.
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Thanks for posting your results Marilyn.
I'm not convinced the calcium carb + vinegar test did show anything, perhaps the body is too close to zero absorption to soak up any of the solution or perhaps it didn't craze or maybe that test isn't effective.
Have you tried testing the glaze without the copper (so it is lighter in colour) and see if it crazes? We know copper reduces crazing so if testing without it doesn't show crazing then I doubt it would craze with it. The last images really don't mean anything re crazing as it's a different claybody than what you are using. Any chance you can get some ink instead of using a felt pen?
Only other thing I can think of is to deliberately smash some pots with this glaze on it and see how they break. This seems like a last ditch approach though as you would need something to compare the results with. https://digitalfire.com/glossary/fired+strength
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First 2 images (pot and test tile) really look they were in a firing that cooled slower than the pot in the 3rd image. Rate the kiln cools at can easily have that dramatic a difference in appearance. More matte and paler colour in a slow cooling kiln vs a kiln that cools quickly (like your test kiln would).
10 hours to do a ^5 glaze firing in a small kiln with no slow cool is a long time. Did you use a bisque fire setting going to ^6 by any chance? was your kiln new when you bought it? if not what do the elements look like?
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Hi and welcome to the forum.
I did a quick Google search and found the recipe you referred to. For that recipe it is parts by volume not weight. So it can be a soup can, a pail or whatever, just use the same container and measure each ingredient by volume with it. Are you looking to make a sculpture or highfire claybody or ?
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7 hours ago, Kakes said:
Do you think MOR would also indicate chipping resistance?
I'm not so sure it would. For testing MOR a three point support system holds the sample piece while pressure is applied in the middle of the sample until the sample breaks. (I simplified the process) In real life this isn't what happens. We bang or drop a piece and it chips or cracks. Lots of variables as have already been mentioned plus there are factors such as sintered vs vitrified, clay density, particle size etc. If you have concerns then look into which couriers cover breakage plus what the cost and coverage is. There are many articles online about how to best pack ceramics for shipping.
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Do you have any "Gold Off" acid paste? Article attached here where the author says if the decal is fired cool (like cooler than ^015) it sometimes works. Given that decals are made from china paints I'm not sure anything will work other than starting from scratch if the pigments have fuzed with the glaze.
Wild earthenware question
in Clay and Glaze Chemistry
Posted
I wonder what would happen if you apply both a physical change (particle size) plus a chemical change to the clay?