Callie Beller Diesel
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Posts posted by Callie Beller Diesel
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If we’re taking bets, I call iron in the water being the culprit. It’s the one constant variable across all OP’s tests so far. Very interested to see how the distilled water variation turns out.
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@AndreaK I think you’re probably relatively local to me, so I assume we’re talking plainsman clay at least. Does the studio you’re looking at do commercial or homebrew glazes, and what kind of work are you thinking you’d like to make?
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Ferric chloride isn’t necessary by any means. I haven’t done a whole lot of pit firing, but I did a couple back in college. You can get some lovely variations with terra sig on its own, especially if you’ve got a light and a dark colour to create contrast with.
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On 4/13/2024 at 4:16 PM, wens said:
Maybe I should give up some control.
Probably.
Part of the fun of working with found materials is the variability. Sometimes close enough is all that’s needed.
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I use a talisman at work, and while it’s great for 10 gallon batches of glaze, it would be wildly impractical in my home studio. The cleanup of the brushes is a pain.
I have a smaller sieve that sits in a 5 gallon pail at home, and I use a large round sash brush to push the glaze through. It works pretty fast and cleans up very easily. -
5 hours ago, Gonepotty said:
Bottom shelf was densely packed...would this impact the firing.? Typically, my kiln is hottest on bottom shelf and coolest ontop.
Yes. Yes this will affect things. If your kiln is hottest on the bottom and you’ve packed it tightly, but your ware still isn’t getting the heat, the bottom is probably packed too tightly. You may also be going a bit too fast through the middle parts of that firing. 120 C is a really fast rate of climb. And yes, it’s not unusual for a bisque to go for 10-12 hours. Keep in mind the elements aren’t on at full power the whole time. If you’ve got the touchscreen, check out the diagnostics in the last firing. It’ll tell you what your energy usage is.
Re: the density affecting the heat: Electric kilns are sometimes programmed to emit more heat on the bottom elements, because heat rises, and they’re trying to avoid cool spots in the bottom of the kiln. They’re assuming people pack it evenly, and they don’t expect consumers to have to compensate their loading habits on a new kiln.
If the bottom part of the kiln is packed particularly densely, especially compared to the other shelves, the heat may not have time to penetrate all the way through to the middle of the bottom layer. If the cones aren’t bending on that bottom shelf with a 20 minute soak at the end, that bottom layer and even the middle is probably playing catchup to even hit cone 09. Try slowing your second segment to 90 or 100 degrees C, aiming for the proper cone 08 temperature, and packing the kiln more evenly.
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Hi and welcome!
It is possible to get durable ware at earthenware, midfire and high fire temperatures, but there are different considerations at each of those points. I won’t use the term food safe, because it’s a bit of a misnomer, and legally only covers whether or not the glaze has cadmium or lead in it. When we talk about glaze durability, we want to make sure that the clay is fired to a point where it would have less than 1% absorbion, the glaze doesn’t leach anything, isn’t crazed, resists both scratching and cutlery marking, and is easy to clean.
With earthenware in particular, you have to be mindful of glaze fit, because earthenware clay remains porous when fired to maturity, and many will glaze the piece all over, and use kiln stilts instead of leaving a bare foot. You have to be extra mindful of your glaze chemistry, because the low temperatures tend to mean the fun, pretty glazes can sometimes be prone to scratching because they’re lower in silica and alumina.
- Kelly in AK and Hulk
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If it’s one of those ones from Amazon, you may be out of luck entirely. They don’t have a good reputation for replacement parts or service.
There is, however, and old trick you can use that may save you some searching. Place a sponge against the edge of the wheel head, and it’ll absorb most of the slip that flies off the wheel as you throw.
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Juried exhibitions or invitationals through galleries have never netted me any sales. They can be a nice ego rub, which has its own value, but that value isn’t monetary IME.
Juried fairs or markets however, are a good thing. Juries can help put together a crowd of compatible artists and quality of work, which helps get it in front of people who are interested in such things.
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Birdie Boone, Shprixieland Studios, Naomi Clement and Sarah Pike are 4 artists I can think of off the top of my hand who slab build and leave exposed seams. All have WILDLY different work from each other. Google for comparison: you’ll feel better.
Unless your work also has a lot of other design features in common with the image you linked, the person who says you’re copying is out to lunch.
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I wish I could remember where this piece was installed, or who made it, but an artist made a whole bunch of thinly trimmed porcelain bowls, and floated them in a pool of water with a gentle current running through it. The bowls rang and sounded like wind chimes when they bumped into each other. It was incredibly soothing.
My initial inclination for question three is to say that I’d prefer to interact with a piece rather than have a constant sound, but I think that subtle environmental interactions could count towards that.
- Hulk, Pres, pottery007 and 1 other
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Toxicity is a whole entire subject by itself. Mostly we have to start with definitions to help clarify.
Tl;dr, yes you can put this glaze on the outside of a pot and it will be fine. It’s not touching food. It melts fine at cone 6, it’s just a “soft” glaze.
When a raw material is labelled toxic, that means it’s toxic in its current form. Once you put a material into a glaze with other materials and fire it, it becomes another material entirely, with different properties. If you’re using a commericallly mixed glaze that is labelled non-toxic, that means it’s not toxic in the unfired state. (It’s probably not toxic in the fired state either, but you’d have to test it to confirm, and manufacturers can’t say that it is for sure under all circumstances without legal problems. People do weird and unexpected things.)
When we’re talking about glazes, most often the finished glaze is more safe than, say, raw lithium. So potters should be concerned about their own health and safety first, and the end user second. Materials like lithium can be handled safely with sensible studio hygiene practices, and can be beneficial in a lot of good glazes.
When knowledgeable glaze chemists talk about food safety, we aren’t talking about whether a glaze will leach Bad Things (TM) into food. This is a very infrequent scenario outside of lead use, and lead hasn’t been used in most handmade pottery for decades now. But we are thinking about craftsmanship and durability. We’re asking questions like Does this glaze have flaws like crazing or pinholing, that can affect structural integrity or possibly harbour bacteria? Does this glaze scratch, or does it cutlery mark? Does it stain easily? Is it easy to clean? If those problems are solved, leaching is usually a non-issue.
Re the silica question: You need 3 types of components in the right proportions in a base glaze for durability: silica to form glass, alumina for strength and to make it not run too badly, and different metals that make silica and alumina melt at much lower temperatures than they do by themselves (fluxes). Without enough silica or alumina, or if those things are in the wrong proportions, the glaze may react to acids found in many drinks, bases like in dishwasher detergent, or may scratch or cutlery mark. SCM doesn’t supply enough silica for durability, but the strontium is also a problem.
Within the flux category, there’s a bunch of stuff that’s a good idea to use in combination, because each material has beneficial and undesirable properties, and mixing them can bring out the best (or sometimes worst) of both worlds. For example, sodium is a strong flux, which is needed to bring down the melting temperature of silica and alumina, and is in most glazes. However, it tends to make glazes craze when by itself. But if you mix it with calcium (or barium or strontium or lithium and a few others), you can still get the melting, but less crazing.
The calcium/magnesium/strontium etc group of fluxes also give you different colour responses, or can help create matte effects if the proportions are high enough. One of the drawbacks of using strontium or barium though is that neither is very high on the Moh hardness scale, so if you use too much of it, the resulting glaze can be prone to scratching, staining or other flaws. But it helps create that really cool matte surface because it promotes crystallization, so sometimes creative folks make trade offs.
- dhPotter, Kelly in AK and Hulk
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Also, were the blistered pots in the same part of the kiln as the non-blistered ones, or were they in different parts of the kiln? If the blistered ones were on the same shelf, can you determine if that shelf hotter or cooler than the others? Were there factors like pack density at work that might have created a bit of a heat sink?
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Steven Hill was the one I encountered who did the strontium substitution and other alterations years ago. I took a workshop from him sometime around 2003, and the SCM glazes were on his glaze handout sheet. He was careful to say that SCM was never meant to be a liner glaze, and was intended to be a base for other glazes to be sprayed over for special effects. It makes sense when you look at his work.
He substituted the strontium in to the Coleman recipe because barium was becoming an anathema at the time, but also acknowledged that both materials are on the soft side. Both can be prone to various forms of erosion when they’re out of balance.
I was going to add this link just as an illustration of his work, but he also talks a bit about SCM on this page.
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Usually M390 is a VERY smooth clay. So if you’re finding it’s got some texture, it may well be the 60 mesh version. My supplier brought up the possibility back in January.
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On 3/27/2024 at 10:06 AM, Min said:
It seems like you are going through an inordinate amount of glaze testing to solve what really appears to be a clay problem
This. 100000X this. If your clay body is giving pinholes of some kind with several glazes, it’s the clay body, not the glaze or the assorted firing cycles. It may well be that an ingredient in the Laguna body just doesn’t want to play nice, whatever is done with it. You have to weigh wether you like using this clay more than you want a perfectly defect free surface.
If you need a good red clay/white glaze combo, M390 and Ravenscrag slip 80/20 with frit 3134, and 2 opacifiers of your choice. (I recommend a tin and zircopax combo if you don’t want any titanium variegation). Reasoning: they give different qualities of white. Tin by itself is very soft, and can be grey-ish or even drift towards a violet in certain light when used on M390 in particular. It’s also expensive. Zircopax by itself is very stark, and gives a very “bathroom fixture” white that resists breaking or pooling. The 2 together give a soft white without weird tonal casts, gives a little more visual interest and offsets the end price of the glaze. I use a max of 10% opacifier, but judging from the look of your photos, you might want a slightly more translucent version, so you could see what happens with 7 or 8%.
I fire with a very analog kiln at home, so I can’t give specific numbers on ramps and speed. I slow my kiln down around the carbon burnout stages mentioned in the Steve Davis article, and I judge that through the colour of the kiln. I’ve recently started working at a place that has brand new Bartlett 2 touchscreens though. I feel spoiled! They are to be preferred over my methods.
I think speed of bisque is more important than end temperature, so slow through the appropriate zones. I think the Naomi Clement one is a bit of overkill. The 12-14 hours of Davis’s cycle (assuming no drying soak at the beginning) is plenty long. Note the pauses around 1500F that both Clement and Hulk have suggested.
The glaze cycle I use to get what is effectively cone 7 is a drop and hold, similar to what you’ve already worked out. I go to cone 6 with a 20 minute hold after the drop.
Note that there will be upcoming changes to M390: according to my supplier, Plainsman demand has gone through the roof lately, and they’re struggling to keep up. They have one clay mixer that they have to cycle all their different clay bodies through from lightest to darkest. While another one has been ordered, it’s not expected in until next year. In the meantime, they’ve made the decision to remove the 80 mesh sieve from the machinery in order to get the clay to go through faster. This will affect M390’s texture starting this year. So we’ll all have to revise some porosity testing until they get the new machinery in place.
The last suggestion I would have is another bisque cycle. But this time, only go to 010. There have been a few reliable potters in various internet spaces lately speaking about this (For Flux Sake podcast in particular). I believe the argument is that the application a more porous clay body gives a dipped glaze results in fewer defects. I haven’t experimented with this personally though, so that one is a shot in the dark if nothing else works.
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If you’re in the UK, you might also check German suppliers. There’s one of them at least that sells a really large selection of grog types which I would assume to include different feldspar meshes, but their name has completely left my mind. I did find this website, which does have an English translation that bodes well. They carry a few different kinds of feldspar, and could be a better source of info on a supplier that’s at least somewhat closer to home.
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Chiming in a little late on this one, but you mentioned the crack in your piece happening at another studio, where the bisque cycle is unknown to you. I strongly suspect the cause wasn’t the fact that it was bisqued twice, more that the cycle used was likely not suitable for your piece. Two foot pieces are going to need a slower cycle than regular pieces, just due to sheer thermal mass. If the studio’s usual bisque cycle didn’t take that into account, or the kiln pack wasn’t a particularly heavy or even, that would be the most likely explanation to me.
Side note: I just spent the morning going through Ceramic Materials Workshop’s new commercial clay body analysis resource. It’s free if anyone wants to check it out for themselves. So far the submissions are limited to assorted clays in the US that are in the roughly cone 6-10 range. Bill’s statement that clays will shrink upon a second bisque depend greatly on what the first bisque temperature was, and which clay body is in question. If you’re bisquing to a common 06 temperature, the statement of a less than 1% increase is likely enough. If your usual bisque is higher or lower, it might not be. After about 1000*C (roughly cone 04) many clay bodies hold steady for a time before continuing to shrink. If you bisque very low to cone 020, the shrinkage charts actually decrease for a time, meaning the piece expands a bit after the carbonates and chemical water burn off.
Again, this is VERY clay body dependent.
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Hi and welcome!
Just to clarify, do you want it to look different in the bucket, or in the end result?
If you want it to look different in the bucket, food colouring works a treat, and burns out.
If you want the end result to look different, a small quantity of a light blue stain would pop glaze colours better than a brown or grey one would.
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So I’m going to preface this by saying I’ve never fired Obvara, and I’ve only ever fired raku by eyeball, never with cones or thermocouple. (Please do this with proper eye protection). So I couldn’t tell you what temperature exactly I was using, but the glaze recipes used were mostly gerstley borate at the time, and that melts between 1550 and 1600 F.
So my question is, can you fire the raku pieces to a lower temp to match the Obvara recommendations, or are you using glazes that really don’t mature until that hotter temp?
If you do need the hotter temp for raku, it’s possible to roughly judge the temp of a piece by the colour of the glow coming off it. The chart linked below has a nice colour gradient illustration, and you can do a bit of a comparison from there. There’s a paywall, but you can use one of your 3 free articles/month to view it.
https://ceramicartsnetwork.org/ceramic-recipes/recipe/Kiln-Firing-Chart-142658
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I’ve seen this form a bunch, and yeah, it’s tricky to get right. One solution for the warping I saw another potter online do was to do all the minimal trimming and cleanup as you describe, but they then added a slip trailed circle of clay as a foot rim. It was just enough to keep the full surface of the plate’s bottom from being in direct contact with the kiln shelf so you don’t get the warping, but still keeps the same aesthetic qualities of this style.
Results may vary with different clay bodies, but it’s something that’s worth a shot.
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Keep us posted! Curious to know what it turns out to be.
Limiting Oxidation on Palladium?
in Clay and Glaze Chemistry
Posted
I don’t know about other lustres, but gold and white gold are made of those actual materials, and don’t tarnish.
Some raku glazes that contain a lot of copper can be prone to reoxidizing over time. Usually folks will coat pieces like that with spray varnish or similar. I think it could work for Palladium.