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Callie Beller Diesel

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Everything posted by Callie Beller Diesel

  1. 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.
  2. 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
  3. I first got hooked on clay because we did raku at my high school. The only time we had anything explode was the one time we tried firing a piece that wasn’t bisqued first.
  4. 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.
  5. Hi and welcome! I wish it was under better circumstances. The pictures are worth a thousand words, and thank you so much for including those! The fact that the piece is broken so cleanly, and in 2 near-perfect vertical lines all the way through means that this wasn’t specifically your clay, or anything you did during building the piece. It’s a nice dense clay that probably stuck to the kiln shelf due to the mass and size of the piece, and cracked during cooling. For the next pieces, I’d fire them on some sand/alumina so that the piece has the equivalent of little refractory ball bearings to shift around on. You could also use a waster slab that will shrink at the same rate as the piece, but take the brunt of the force and absorb the crack instead. If the clay survived the bisque just fine, another possibility is to not fire the piece to full clay maturity. Porosity in the end piece is less of a concern for you than it would be for someone throwing functional ware.
  6. Are you sure that’s iron oxide? There’s lots of other possible solubles that turn brown.
  7. While I add dry ingredients directly to my old batch at my personal studio all the time with no ill effects, if you’re in a teaching studio, you might want to mix the new batch separate and test it to verify everything went as expected before adding it to the old batch. And depending on how well the studio members/students are mixing the batches, you might want to let it run out as far as possible before adding new. If incomplete mixing is a habit, it can mess with the glaze.
  8. This one from my students. If you manage to wear the skin off your pinky, vet wrap is a good way to protect it.
  9. If you can’t get proper pottery plaster for a reclaim slab, you can lay an old sheet over wire racking and lay thick slurry out on that to dry.
  10. I used paper clay for a couple of years. It lives up to all that hype! It’s much more forgiving about when you attach pieces, so if you’ve got time constraints, it’s a great material. The 2 main things you want to watch are the stink from cellulose breakdown, and to be mindful that then end piece will be somewhat more friable than the same piece made out of regular clay would be. How much more friable will depend on how much pulp you add. The rot can be managed in a few ways, the easiest being to only mix up what you’ll use in a short time frame. The next easiest is to prepare a larger batch, and dry it out in really thin sheets that can be stored and rehydrated as needed.
  11. If the mixture is homogenous, the shrinkage rates should wind up somewhere in between the 2 different points. You’re making a whole new clay body.
  12. In all the years I had to transport work for firing, I found the best fix was to have small sealable sandwich bags of glazes to do touchups when you got there.
  13. @semidoomed if the glazes are only being fired to cone 04 and cooled in a normal firing, the clay body won’t matter a great deal. If they do want to pull the pieces out of the kiln while hot, it’s a good idea to wedge in a bunch of grog if there isn’t any already to help ease some of the thermal shock.
  14. Usually the good liquid wax emulsions do tend to be more expensive than the ones that tend to pill. The paraffin will be less expensive, and I second Hulk’s idea about a crock pot or an old rice cooker used to keep it warm.
  15. Your kiln firing cycle sounds good, although the overnight hold may be excessive. For a 1 cm ( about 3/8” for the Imperial users) thick piece that’s bone dry, I don’t know that more than 3-4 hours is necessary, even allowing for a more humid climate than mine. We use a 4 hour hold at the teaching studio I’m at, and most learners make some pretty chunky pieces when just starting out. The end durability of the piece in your garden will be dictated more by your clay body’s fired properties and how they interact with your climate. Freeze/thaw cycles will be important, and I’d follow whatever recommendations they have in your area for overwintering terra cotta plant pots. Potterycraft doesn’t appear to offer porosity testing specs on their, but they do say it’s reasonably groggy (6/10). With a 30 minute soak at the end of your firing, I would expect your end firing temp to hit 1200, or a good cone 5-5.5. A bit under the cone 6 end point on this clay, so I would expect some porosity in the end piece. Enough to absorb some water over time, especially somewhere damp enough to grow moss.
  16. As a regular red clay user, darker clays are going to have a different effect on glazes than lighter coloured ones do. Even leaving out the possibility of oxide interactions, the dark background behind any translucent/transparent glaze is going to reflect light differently than a lighter coloured background will. If you take this effect into account and work with it rather than against, you can get much more satisfying results out of your glazes, whether they’re commercial or homebrew. Darker clay bodies DO work well with commercial glazes, they just don’t look the same as the sample they only show on white clay, and that’s frustrating. I have no idea why they only show samples on white clay, because there’s a huge range of clay colours out there, but here we are. As a general rule, yes, if you’re using brush on commercial glazes, you will have to add more layers over a darker clay for best results. You’ll need the extra pigmentation to overcome that aforementioned dark background. Even on light coloured clays, a too-thin glaze layer is gonna go that yucky green or brown. With darker clays, doubly so. You may find that variegated glazes, or glazes with titanium or rutile will actually look much better on red/dark clays than they do on lighter lay bodies. The extra iron kicks those rutile blues into overdrive, and it’s really nice. If you want a result that’s closer to the samples, you probably also want to choose more opaque looking glazes, or even add a white slip over your red clay to pop certain colours. Or even use it as a way of getting 2 different effects on a piece with only one glaze. You are not likely to get light or pastel colours to come out true on red clay, unless they’re highly pigmented or contain a lot of opacifiers. Even then, they’ll have a more tonal cast to them.
  17. @Crooked Lawyer Potteris your kiln vented? I’m not sure if it’s the atmosphere or the temperature that’s different, but if you’ve ever had a chance to look inside a pot that’s at temperature, usually either a raku or wood fire where you could see inside the kiln, you can see that there is indeed a difference in the glow on the inside bowls and cups, and it moves with the kiln’s atmosphere. (My optometrist would like a word with 20 yo me.) If that fluctuation is from gasses from the kiln atmosphere, or even from materials decomposing and being contained in more upright forms, venting might take care of it. I notice that your bisque temp is quite low as well. Have you tried going up to cone 06 for the additional burn off?
  18. 50 years ago, the standard was also cone 10 reduction, and I think cone 6 was filed under “interesting but impractical.” So the extra heat work took care of the difference that the silica mesh size would have made. 200 mesh sil-co-sil was all I could get back in the 90’s, so I used it. And I was firing at cone 10 at the time, and it was fine. When I made the switch to cone 6, I came across much of the same info you’ve already listed, and the 350 mesh was more available. I was less concerned with crazing at the time, but I can say that the mesh size makes a difference in glaze clarity at cone 6.
  19. If you’re making functional ware, spray paint isn’t going to be a good route. Sculptural stuff? Cold finishes all the way. It opens up sooooo many cool possibilities.
  20. Mostly throwing large amounts of items on a slow wheel with soft clay is an exercise in economy of motion. In the absence of knowing exactly what you’re doing/not doing, it’s hard to troubleshoot exactly. A good resource to check out might be YouTube though, because sometimes a video can reveal a lot in a short amount of time. If you find it difficult to watch a video tutorial, something that can help is adjusting the playback speed. But if you need text versions, I’ll tag @PeterH, as he’s got a gift for tracking down all kinds of good articles. I’m curious as to why you’d want to use a kick wheel if you’re going in to production pottery though. Kick wheels tend to be harder on the body than electric ones, and that’s an important consideration when you’re looking at a job that can have a high propensity for repetitive motion injuries. Production pottery of any kind is about economy of motion and making things efficiently, so that you can make a lot. Any choice made about how you work that isn’t about efficiency has to have a compelling reason to be included in your process. If you’re using a particular technique that takes more time, you have to find ways of offsetting that elsewhere in the process. Or the results have to be able to provide enough value in the finished work to be worth the effort.
  21. @tyler it could be a good idea to check with your local clay supplier if anyone who can do that for you. Every clay person I know likes to talk about what they like (clay) to anyone who will hold still long enough to listen to them. They’ll know someone who knows someone.
  22. Usually I work things pretty close together, so I don’t need a lot of “long term” (more than a week) storage these days. Mostly I use a double layer of plastic to cover things, but I did get a large under-bed plastic tote for handles that I use in a similar manner to what you describe @Pres. I have to ask though: why the board or plate over the sponge? I’m picturing a small throwing sponge or similar, as that’s what I use.
  23. I found a reference on the Laguna website that said they acquired the Westwood Ceramic Supply company. I’d suggest reaching out to them. I didn’t find any glazes in their current catalog with a WR number, but they may have older records.
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