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Min
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Posts posted by Min
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1 hour ago, neilestrick said:
Crazy that they just had it sitting out in the open where anyone could bump into it. Bad planning on the part of the gallery.
or was it? media coverage, competition from others wanting to purchase the shards, hmmm
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Hi Claire and welcome to the forum!
Yes you could use slabs for a sink that size. 4 - 6 mm thick slabs should be fine. I would miter the corners so there is more surface area for the joins. I know there are many broad firing range clays used in the UK, I would suggest using one that you can fire to the top temperature to get a strong mature body.
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Thanks for posting the link. My hunch is this comes down to expectations and the history of how glazing and firing methods evolve. We in western cultures seem to prefer "flawless" surfaces; pinhole and dimple free yet in other cultures pinholes and dimples add beauty to the pot. Reading some of the old clayart posts by Lee Love (who lives in Japan) mentions bisque firing to ^012 or cooler. Doing this is going to make a much more fragile pot, I would imagine glaze tongs could very well break some pots. Porcelain bodies have much less junk to burn off, you can get away with a cooler bisque for those bodies than say a high manganese body if your goal is to have a pinhole/dimple free pot. I believe it was Ron Roy who was one of the champions for raising bisque firings to ^04, many people have had success with this. I remember when I was learning about firing the norm was to bisque to ^08 - 06.
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@steviepeas, could you post a link to his? Might be another factor we don’t know about.
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4 hours ago, Babs said:
I seem to remember somewhere soaking pots with milk was the go.
- High Bridge Pottery and Babs
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On 2/19/2023 at 1:13 AM, Bill Kielb said:
The Katz — Burke has extensive color test and ought to be easily adjusted from its present matte to semi matte, etc… by testing and increasing the silica in small increments till your desired sheen is achieved.
Is this the recipe you are referring to? https://glazy.org/recipes/16540
I would be surprised if a high alumina + calcium matte such as that one would give the smooth buttery feeling matte the op was asking about. In my experience it's a magnesium matte that gives that silky buttery type of glaze.
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@laurasaurus, I bought that controller when I upgraded my PSH/Euclids kiln that I use for bisque. (I have the same kiln, 1991). Original controller was very rudimentary and many of the numbers on the touchpad no longer worked. If you are thinking of getting a new controller I would ask Jay or whoever you are dealing with at PSH if they have a reconditioned controller or one they have taken off a kiln for an upgrade. I got a used controller from PSH about 5 years ago with about 100 firings on it, saved a few dollars.
We set it for using 2 tc's, there is room on the board for 1, 2 or 3 tc's. Given that I used this only for bisque I went with using 2 tc's. As you are using this for glaze firing also having 3 tc's would probably be very helpful, makes firing an even kiln load easier than relying on stacking alone.
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3 hours ago, Hulk said:
Is palladium typically used for non-functional work?
Only?
Yes! Definitely not a glaze for surfaces coming in contact with food.
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9 minutes ago, Pyewackette said:
OK I give up. What's a habachi? Google thinks I spelled hibachi wrong ...
It means Babs was a hippy!
It's one of these things.
- Pyewackette and Rae Reich
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On 2/16/2023 at 2:06 PM, Babs said:
Now wondering ehat dud happen before plastic.
Damp cupboards and fabrics perhaps?
- Pyewackette, Babs and Rae Reich
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@Ben xyz, to keep a glaze from running when you don't want to change the formula either apply it thinner or make a physical barrier such as a shallow lip or rim or edge around the edge or foot of a pot. Is firing it flat and getting gravity to help an option?
Reason it changes over the years is it's heavy in manganese which will oxidize over time.
@Bill Kielb, lovely work, is that your wife's lettering?
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I got the original recipe to come out pretty close using Ferro 3110 and a few other changes, included some epk to help suspend it. Sodium and potassium are different but the total of the two is the same. Ratios are the same also. If you have some spodumene already you could try a test with it however using Greenbarns pricing this actually works out more expensive than using lithium carbonate although the lithium from the spodumene will be less soluble than from the lithium carbonate. (like with any recipe, if you try it test a small amount first)
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I would be really doubtful the recipe uses colemanite. Greenbarn doesn't stock it and they haven't for years, I'm thinking Lin's studio uses gerstley borate in place of it. If this is the case then the formula with gerstley borate has the boron at only 0.05 which in conjunction with the lithium makes me think this was a cone 10 glaze recipe that someone added the lithium in order to bring the firing down to ^6.
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@LinR, where are you buying your lithium carb from? Greenbarn price is $183.30 / 500 grams. I agree with you, maybe it's time to look for another recipe.
1 hour ago, neilestrick said:US Pigment has lithium carb for $65/lb, and that recipe only uses 1 pound for a 5 gallon bucket. Where's the $400 coming from?
65 USD to CAD makes that 87.50 CAD plus a couple percent for the transaction plus shipping plus duties plus Canadian taxes plus if a courier vs US Postal Service is used there will be their fee on top of that. If it's for a business there is also the joy of the paperwork declaring the products for a business when coming across the border if you have it shipped to a US address then drive down to pick it up. Still doesn't add up to $400 though.
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Really sounds like there was an issue with the batch you got rather than a fit issue with all 15 of your glazes.
What I would do in your situation is make up some tests with increasing amounts of silica added to the body then try it with one or two glazes and see if it still crazes. I would add increments of 5% silica (200 mesh) and see if the crazing is reduced. I would dry out some unused clay (not trimming scraps) weigh out dry clay into four 100 gram batches and add 5% silica to the first, 10% to the second, 15% to the third and 20% to the fourth. Add some water, slurry mix it then dry the slip on plaster until you can wedge it up. Make some test tiles with the clay, bisque as usual then try one of the glazes you know should fit the clay. Document every step with photos then see if the glaze crazing is reduced or worse. Send your findings to Laguna with an offer to send them a sample of the clay so they can test it themselves if you still aren't getting satisfactory help from them.
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Try sending @Marcia Selsor a pm asking her about this.
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16 hours ago, Ben10 said:
I heard that people probably use special glazes for bone china which usually contain bone ash. Does anyone has experience with that? Is it necessary?
It isn't necessary to include bone ash in the glaze recipe.
I believe @Hyn Patty uses bone china for some of her horses, try sending her a pm. (click on her name then the little envelope at the top of the screen and follow the prompts)
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US Pigments products for sale re lead:
Red Lead https://uspigment.com/product/lead-red/
White Lead https://uspigment.com/product/lead-white/
Lead Bisilicate (aka fritted lead) https://uspigment.com/product/lead-bisilicate/
Lead Chromate https://uspigment.com/product/lead-chromate/
So if someone wanted to make lead bearing glazes in the US or anywhere US Pigments ships to it wouldn't be hard to do so. I haven't seen commercial glazes containing lead for quite a few years in Canada.
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I read "Mr.Burt" as saying he thought this was a body problem more than a glaze problem. Also, if they are firing lead glazed ware we know that some forms of sulphur don't burn out until 700C - 1150C, which could mean much higher than lowfire lead glazed ware matures.
1 hour ago, High Bridge Pottery said:the question is do I really have to get rid of bubbles you can only see through a microscope when the glaze layer is thin?
I wouldn't worry about glaze bubbles not seen by the naked eye, but could be a fun challenge to give yourself.
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Organics in the bisque fire not adequately fired off during bisque, lead glazes and reduction firing seems to be the gist of the quotes above, just wondering how much of this is relevant to the work you are doing now?
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But we already know boron is a glass former though.
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Laguna gives COE figures for their claybodies, I realize they probably are not super accurate but they would probably be okay to look at for a ballpark range. Frost is posted at 6.99 which is really high compared to most of their claybodies which in theory should mean it does not require a low COE glaze. Also, the ingredients used to make it are minimal, halloysite, nepheline syenite, silica and bentonite. I don't recall reading anything lately that said those materials have had any major chemical changes.
Could you post a picture of one of the mugs with the "Strange crazing, like a single almost stress looking crack down the side..." and the glaze recipes you used on those. And then a recipe for one of the glazes that had regular crazing.
Have you contacted Laguna with the batch number and asked them about the issues and if there have been any changes to the claybody? I'ld send them some photos of the cracks and crazing along with corresponding recipes also and see what they have to say.
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Thanks for finding those equations Joel. I'm wondering if its just adding another variable and / or a different equation that is muddling the difference between the SiO2:Al2O3 ratio insofar as looking at those levels (in addition to having the flux ratio of 0.3 R2O:0.7 RO) to determine with math whether a glaze will be an alumina matte, gloss or somewhere in between without looking at slow cooling glazes and or different flux ratios that employ more than the one mechanism to get a matte.
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You could ask Euclid's if they would wind them for you. Send them all the info off the faceplate, kiln measurements, photos and any other info you have and see what they have to say.
Biscuit Firing at 800deg centigrade
in Clay and Glaze Chemistry
Posted · Edited by Min
@High Bridge Pottery, re temps and what is happening in the bisque firing, do you have a copy of Hamer's The Dictionary of Materials and Techniques? If you do have a look at "Firing", it goes through all the stages and temps etc, really thorough read. The figures mentioned by Hamer mesh with what is in the pdf by Steve Davis below. (also the bit from GlazeNerd above re inorganic carbon burn out range) Includes organic carbons and sulphur etc also.
https://www.aardvarkclay.com/pdf/technical/Bisquefiring.pdf
@steviepeas, if you are making functional work that is to be used with liquids, it is best to use a clay with less than approx 1.5% absorption. With wide firing range clays, like so many are in the UK, it's best to fire them to maturity then check the absorption. If a clay is fired to less than the top maturity temperature / cone then it's apt to weep moisture if not.