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Min
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Posts posted by Min
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Just to clarify you are firing lowfire glaze to cone 05 on a lowfire body that has been bisque fired to cone 04? Or cone 6 glazes on cone 05 and 04 bisque? How fast are you ramping up the kiln for both bisque and glaze? Is it possible to do a hold/soak with this kiln?
Are the glazes your recipes or commercial ones? If they are your recipes could you post a recipe or two that are giving you problems?
What claybody are you using?
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14 hours ago, LeeU said:
if I used Manganese Wash
Is this the commercial Amaco Wash you are using? If it is I would try brushing it on the wiping it back with a damp sponge to remain in the recesses then apply a glaze over top. I think leaving it without wiping it back would be too intense. Whatever glaze you use will dilute the intensity of the Amaco Wash.
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If it hasn't been fired on yet then yes it can be dusty.
It would just be a guess but the least expensive materials to use in a kiln/ batt wash would be kaolin and silica so if companies are trying to save money with the wash they supply they will load the wash up with that and skimp on alumina hydrate. There is a link below discussing kiln/batt wash with some tried and true recipes (it's towards the end of the link). Also, I would suggest wiping it back from the edge about 1 cm and wipe off any drips from the side of the shelf.
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@MsBeth, for the fondant molds are you using flexible silicone molds?
I think there is a bit of confusion with the terminology being used, when you say "clay castings" is seems like you are using casting slip. But then "press the clay into the mold" sounds like you are using pugged soft clay.
I have used flexible silicone molds and soft clay, I very lightly wiped the molds with veg oil then pressed the clay in then flexed the mold enough to have the clay pop out. There was a bit of distortion with the molds with undercuts but it was easily fixed since the clay was soft.
Dusting molds with cornstarch is also an option, don't have to be concerned with airborne silica with it.
Welcome to the forum.
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15 hours ago, nuna said:
Bisque super low at cone 020 or so. In this case, would it be safer to fire it fast or slow?
Slow. Both for firing up and cooling down.
These pictures are from Digitalfire of lowfire ware, pots have cracked from uneven cooling, edges will have cooled faster than the middle area of the pieces. The way to avoid this is to have the cooling down go as evenly as possible. Slow the cooling down between 1150F - 950F, I go at 100F/hour through this zone with suspect work.
There is negligible shrinkage, ie less than 1% between bone dry greenware and bisque firing to ^06- ^04, would be interesting to see data that shows refiring to a lower temp causes more shrinkage.
edit: when having your piece in the kiln put it between shelves, not at the top or bottom of the kiln, this helps the heat even out also. I put rectangular or triangular kiln posts around the outside edge of the shelf also. (round posts can roll)
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On 3/13/2024 at 9:59 AM, SSerrano said:
Thanks for your quick response!!! Any guess how much food coloring I should add? I have a tote of slip that's about 150 gallons.... maybe a pint or 2 should do the trick? Crazy question, I know.
If the food colouring is just to tint the raw slip then I would suggest using paste food colouring rather than the liquid, it goes much further.
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If all else fails MAGMA really should work to suspend iron spangles. I've noticed it can be listed as out of stock at Brackers quite often, if you decide to try it I would suggest emailing them and asking to let you know when it's back. It does thicken the glaze a fair bit and slows down the drying time so that needs to be taken into consideration.
https://www.brackers.com/magma-miracle-anti-gravity-multipurpose-additive/
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Hi and welcome to the forum.
Link to the Ceramics Arts Daily Tried and True Raku Glazes here if anyone uses any of these recipes.
Giving this thread a bump, hopefully someone will chime in.
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5 hours ago, Katie S said:
She expected that it needed to be fired to cone 10 for a bisque firing, which sounds wrong to me. I asked her to check the bag/brand and she was gifted it from an old friend and has no idea what the brand is.
If she isn’t absolutely 110% sure it’s a cone 10 clay then I would pass on this.
5 hours ago, Katie S said:She doesn't plan on doing a glaze firing.
This makes sense to fire the clay to maturity / cone 10 if she doesn’t plan on glazing it and it is indeed a cone 10 clay. She might want to leave it as bare clay or be planning on doing a cold finish on it. Firing to maturity would be a clearer way to describe what she wants rather than calling it a bisque firing. A mature body is far stronger than a bisque fired body.
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The concave then convex side design might also be contributing to it being pulled out of round.
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@Potpotpotter, slow cooling is different from a drop and hold/soak. With slow cooling the preprogrammed slow cooling schedule will be something like 9999 (freefall) from the last temperature in the program down to 1900F then 150F down to 1500F. If a glaze is already a matte without this slow cooling then by adding one you could very well end up with it being far more matte. This schedule is a basic slow cool for functional glazes, many people do their own custom slow cool schedules to suit their glazes. Slow cooling promotes certain glaze characteristics such as micro (matte glazes) or macro glaze crystals or visual textures within the glaze. It helps with some glazes and does nothing for others. Slow cooling is also useful for large pieces to help prevent dunting/cracking.
A drop and hold/soak is helpful to help heal pinholes and blisters. The temperature you hold at will depend on how fluid the glaze is at certain temperatures. There are many causes of glaze pinholes and blisters, glaze thickness, application, glaze chemistry, bisque and glaze firing all can contribute to them.
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I wonder what would happen to it if you scraped some into hydrochloric acid? Interesting.
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There isn't a one size fits all firing schedule to fix pinholes and blisters but somewhere to start would be to drop 100F below your top temperature and hold there for 15 minutes. One other thing I do is for my kiln and my glazes it works to fire below the top temp and soak there to bring cone 6 down then do the drop and hold/soak, (I also do a slow cool for my satin matte glazes but that isn't necessary for many glazes). It can take a few firings to dial in what works for your kiln and glazes.
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On 3/2/2024 at 1:01 PM, chris123 said:
I'm attempting to transition from fully thrown plates to partially slab constructed to save time and effort. The first iteration of the plates are simple with a flat bottom, no foot, and a short turned up (nearly vertical) side about 3/4-1".
I'm seeing a lot of plates made like this these days, it's a good way to make a plate with this type of design. I've got one bisque fired as a test but haven't got it glazed yet, it was really fast to make and I also like that it doesn't require any trimming. That nearly vertical edge is going to help prevent sagging/warping during the glaze fire compared to a flatter more horizontal rim.
I would suggest putting one of yours in a glaze firing with no glaze on it, if it doesn't warp then it would suggest the glaze fit could be the problem.
Welcome to the Forum.
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I stumbled across this Etsy listing where someone is selling feldspar granules, does this help? I know some people use chicken grit (not the oyster shell type) for big chunky inclusions in claybodies also.
@PeterH, do you know of anywhere in the UK to buy it?
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Have you tried contacting them and asking if they have any other advice?
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From the article linked below from Charlie and Linda Riggs, they put the pot within minutes of applying the slip into the kiln and not to allow the slip to dry at all. Is this the way you are doing it also? I wonder if adding gum to the slip would help?
(behind a paywall but can access 3 free articles a month)
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Bloating for sure is caused by overfiring but then there is also blebbing.
I think that in the last 20 years or so the term bloating is used to cover both bloats and blebs but with pyroplastic claybodies, such as many of the smooth white bodies, an air bubble within the clay wall will expand during glaze firing when the glaze has melted enough to seal the surface of the clay and the air pocket expands causing a bump on the surface of the clay. These don't show up during the bisque but do show up during the glaze fire, does't have to be overfired to happen.
- Kelly in AK and Babs
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Bendy foam hair roller from the dollar store, I use them for supporting the rims of slab pots etc and also around the handles of the glaze tongs. I slit them up the side then tape them on, saves rubbing the skin sore between my thumb and index finger on a long glaze day.
- Rae Reich, Hulk, Kelly in AK and 1 other
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5 hours ago, Vik said:
I'm wondering if it's possible to streamline this process by adding the 10lbs of water directly into the original bucket of low glaze and starting the mixing and sifting process from there.
Yes.
Most glazes are just fine with running through an 80 mesh screen once, some run it through twice. I hold a bit of the water back to rinse the sieve out at the end of sieving to try and get as much out of it as possible.
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On 2/25/2024 at 9:18 AM, mrcasey said:
I appreciate your reply and agree with you, but do the manufacturers state anywhere that this is ok?
It seemed like a given that they can and many of us do this but I reached out to the Ceramic Shop to ask them specifically. They make, sell and wholesale posts to other ceramic suppliers in the US and elsewhere. (they make triangular and square ones)
Their reply:
"Thanks for reaching out!
To my knowledge, yes, they can be used on their sides. Kiln posts are made to be the most stable on their top ad bottom though and they will take up extra room in the kiln on their side. If you need a smaller kiln post for some works you can check these out: https://www.theceramicshop.com/product/148/kiln-post-1/
All of our kiln posts are rated to cone 10.
Best,
Syd"
Wollastonite lumps revisited
in Clay and Glaze Chemistry
Posted
For sure you can get the chem to match using silica + calcium carb for wollastonite. I've done the reverse with recipes calling for calcium carb and subbed in wollastonite and reducing the silica in the recipe so the formulas match. What I found was the wollastonite versions melted noticeably more. Some recipes won't show a difference, depends on glaze mobility and how much CaO is involved. I think another factor is the mesh size of the silica being used in the recipes. Perhaps very fine silica, ie 90 micron compared to 45 micron would show a difference in the melt if used with calcium carb? I've always thought of wollastonite as being like a frit, albeit a lumpy one, it melts really well and with minimal LOI.