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Member Since 31 Mar 2010
Offline Last Active Oct 21 2016 10:22 PM

#114958 Brush-On Stoneware Glazes

Posted by Min on 20 October 2016 - 01:30 PM

Hi Caden and welcome to these forums.


Yes, common practice is to bisque to 04 and glaze fire to 6 for a cone 6 clay, be it stoneware or porcelain. 


For porcelain that gets really soft and slumpy when firing to maturity then the piece can be supported while firing to top temp then glaze fired with low firing glazes but for studio potters that is not very common at all.

#114921 Water Seeping Through

Posted by Min on 19 October 2016 - 06:58 PM

I totally and completely disagree with what your supplier said. Load of rubbish. Pots that are meant to be watertight must not leak even when there is no glaze on them whatsoever. A 10 minute soak is going to do diddly squat to the absorption of a ^6 clay being under fired.


Like Mark and Bruce said get a clay that matures at the cone you are firing to. A water tight low fire clay is going to be hard to find. Most clays list their absorption rates, look for one under 2%. (some clays are okay a bit higher than this) Make some test pots by making flat based cylinders, scatter them throughout the kiln, some in the middle of the kiln to allow for thermal lag there. Fire the pots to the proper cone with no glaze either inside nor outside.  Fill them with water and put them on a couple sheets of newsprint for a week. There should be no wrinkles in the paper after that time. I make a lot of French Butter Dishes, water is in the base of them 24/7, just like vases they need a tight body. Once you find a clay that works I would re-test it when you get a new batch of it to be doubly sure.

#114882 Rim Lock

Posted by Min on 19 October 2016 - 11:13 AM

Quick fix for sticky / too tight lids after glaze firing. Mix some silicone carbide (I use 100 mesh) with a little bit of toothpaste and smear it around the flange / rim and then twist the 2 pieces back and forth. The silicone carbide is abrasive enough to grind the 2 pieces down to fit. (It also makes the edges super smooth)  If you can find water based valve grinding compound that works too.



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#114855 Qotw: Is It "hands Off!" In Your Studio?

Posted by Min on 18 October 2016 - 09:57 PM

Can’t really say I’ve ever had any problems with others in my workspace. If someone wants to be "hands on", well there are batts to scrape, shelves to wipe down, kilns to be unloaded, clay to be pugged, glazes to be sieved, floors to be mopped, oh and they could make me a cup of tea  ;).  It’s a work space, I don’t encourage visitors. Think the biggest threat is me, trying not to trip over my dog who loves to spend the day in the shop.

#114767 Uncommon Functional Forms

Posted by Min on 16 October 2016 - 02:16 PM

Good topic, I'm always looking for new ideas. Netti pots, Compost Jar / Pickling crock, 

this kind of soap dish, but with a shallow rim on the front and back a03f1ad5bfc3c1d8b77e701d3cc82b92.jpg

#114750 Epic Fail Making Slabs

Posted by Min on 15 October 2016 - 09:14 PM

What I find really helps prevent short clay is to save my throwing water, let it settle overnight then the next day I pour off the top water and add the slop at the bottom to my recycled clay. I save it up and add it to my mixer/pugger but you can do the same with recycled clay done by hand. You are adding the fines back into the clay, they help with plasticity.  Also, if you have a lot of clay to pug and not a lot of saved slop then you can whiz some macaloid and hot water together to make a fairly wet gel, let it sit overnight then add a glug of that to the mixer/pugger. (technical measurement there)

#114533 Oven Safe

Posted by Min on 11 October 2016 - 11:30 AM

There is always going to be somebody who puts a cold pot in a hot oven or a hot pot in a sink of water. Doesn’t matter what instructions you give with the pot warning not to do this.  I think this comes down to how comfortable you are dealing with an unhappy customer(s) at some point in time. 


Low COE clay with a well fitting glaze, rounded pot base, even thickness of base and walls, no sharp corners where base meets walls, even drying to avoid building up stress are all going to help. At some point in time if you sell a lot of ovenware it is inevitable you will have to deal with an unhappy customer who has abused the pot and it’s cracked.

#114481 Amaco Opalescent Crazing Badly

Posted by Min on 09 October 2016 - 12:59 PM

I agree with Rae that it’s a fit issue. That clay was developed by D’Arcy Margesson and I know he bisques to 06 and glaze fires to 04. So if you fired it to 03 I don’t think it’s under fired, (unless that kiln load under fired by at least 2 cones). I looked up the glaze and it’s listed as an 05 glaze. So by my logic if neither clay nor glaze is under fired that leaves it as a fit issue. D'Arcy has been using that clay for years, it's very strong for a lowfire clay, the mug I have of his has put up with lots of use. (microwave plus dishwasher)

#114242 Do You Like....?

Posted by Min on 03 October 2016 - 09:44 PM

@Diesel, thanks for that. I had thought about that one but since most of my work is with white clays I had second thoughts about keeping the red and white separate. Somehow it doesn't seem as daunting to keep tan and white clays from contaminating each other. 


@SydneyGee, I don't know if burnishing would seal it up enough to stop leaks or not but I do know I'm too lazy to be burnishing all my pots. :rolleyes:

#113807 Multiple Clay Explosions In Bisque

Posted by Min on 26 September 2016 - 11:19 AM

pssst, air bubbles don't blow up pots. Damp pots do. Set your kiln sitter for 12 hours,  turn on the bottom element to the lowest setting and leave the peeps out. If you are making regular thickness pots then try this candling overnight or at least for a few hours. (don't forget to turn the dial on the sitter back up again before you bisque fire so it doesn't time out)


edit: I just re-read your second post, I missed this bit the first time:  "For a smaller kiln I think an hour per each switch is plenty of enough time to warm up and let any extra moisture escape" doesn't matter what size the kiln is the clay still has to go through the same processes, think you are firing too fast also. 

#113632 Low Fire White Clay Body Recipe For Commercial Glazes

Posted by Min on 23 September 2016 - 02:27 AM

I think this is getting way more complicated than it needs to be.


Totally Ceramics does slip casting with low fire white clay, they are local, they have years of experience, I would just go in and talk to them.


Greenbarn can order in anything from Plainsman, they are one of their distributors. 


Seattle Pottery Supply is a much larger store than Tacoma Clay Arts Center but I'm guessing they both carry only a few casting slips. Both good places, SPS is usually a bit less expensive than Tacoma but I find Tacoma staff are more helpful. Nope, I haven't used that Laguna slip.


A vitrified body, like what Joel posted, is not necessary for the sculptural work you are doing, will cost a lot more to make and bring far more variables into play. I'm sure it has possibilities as would Nerd's recipe but do you really need to start experimenting with it when you are new to all this?

#113550 The Only Absolutely True Rule For Potters. Pay Attention To This

Posted by Min on 21 September 2016 - 08:02 PM

Another absolute truth, if you have a custom order for a pot and just make 1 of it, it will screw up, if you make 2 they will both be perfect. I know this and yet I still go for it (1 oversized butter dish custom order right now, yup just made the 1 :wacko: )

#113467 Causes For Cracks

Posted by Min on 20 September 2016 - 10:38 AM

Another way slightly different to get even bottom thickness is to make one of these depth measuring pin tools. Tap a sewing needle or pin into the bottom of a hardwood dowel, chopstick, paintbrush handle, whatever, then snip it off with side cutters to the depth you want the base. For wide items you use it in a few spots across the base. (this one is for a no trim base on wide pots, the needle is fine so it's kinda hard to see)


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#113211 Low Fire Shino - Is It Food Safe?

Posted by Min on 15 September 2016 - 10:33 AM

@ qwrkygrrl, I use Insight level 2 glaze calc program. Yup, ^6 will give you less headaches for functional pots.

#113159 Low Fire Shino - Is It Food Safe?

Posted by Min on 14 September 2016 - 07:41 PM

Don’t know how much glaze chem you know so apologies in advance if any of this sounds condescending.

In basic terms, a glaze (for food bearing surfaces) needs to have a certain minimum amount of both silica and alumina in it. Alumina and silica make the glaze more durable and able keep stuff from leaching out of it. The flux(es) also need to be within reasonable amounts.

What this means is anything like cobalt, manganese, copper, etc, whether from an oxide, carbonate or stain is not going to stay locked up in the glaze matrix if the silica and alumina levels fall short. The glaze shouldn't loose gloss or show other signs of deterioration over time. The further away from the minimum target level the more unstable it’s going to be.

In the image below, your recipe has been converted to a unity formula. Your glaze make up the figures in the purple box. The other box shows “targets” for a ^04 - ^02 traditional lead-free glaze. Have a look at the alumina (Al2O3) and silica (SiO2) row. I think you can answer your own question about whether this glaze going to be suitable for food.

As far as lithium levels go you are going to have to do your own testing here. I don't like seeing more than about 5 or 6% lithium carb, but I've seen glazes use more than that. You are getting into an area of thermal expansion here. Glazes that are very high in lithia are by nature going to have a lower coefficient of expansion, have to test on your claybody to see if it fits. Lithia can cause both crazing and shivering on the same pot if the level is too high. Shivering glazes are dangerous, you can have a sliver of glaze (glass) come off the pot (usually on rims and high points) and get into the food/bevies. This is how I test a glaze for shivering; make a thin walled cylinder and glaze the inside only with a thick layer of glaze, include the rim but not the outside of the pot. Fire the cylinder then put it in the coldest part of a deep freezer overnight. Frozen cylinder goes in the sink then gets filled with boiling water then the cycle is repeated a couple times. Hopefully nothing shivers off. (don't know if that's the best way to test for it but it's what I do, same test to check for dunting with low expansion glazes - pot will split in two if really bad fit)

Hope some of this made sense.

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