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I recall an issue about 15 years ago that some friends had with clay from CAC, turned out it was from the water used in the clay production. Maybe it's this again?

Hi Kelsey and welcome to the forum! I'ld ask the clay manager at Tacoma Clay Art Center about this. I'll pm you her email address, she might be able to help. Let us know if she can explain it, it's interesting.

There are cadmium inclusion stains available in greens. Here is one example from NZ. https://macsmud.co.nz/products/meadow-green-stain There are also praesidium vanadium greens, more of a chartreuse colour. https://macsmud.co.nz/products/lime-green-stain

#1Pottery Plaster.

Similar look with Jeffrey Nichol's work, multiple layers of underglaze applied on top of the clay then sanded through.

Might just be the underglaze or slip with no glaze on the outside and underside of the pots.

Hi Allan and welcome to the forum! In a perfect world a low expansion clay with well fitting glazes would be the way to go. In reality many people make ovenware from other bodies, the design of the pot also comes into play as does how to use (and not use) ovenware. There are quite a few threads discussing this, one of them here. I would suggest asking your local ceramic supply place which claybody they recommend.

Found the image below on her book of faces page. Maybe u.g. on the slipcast textured blanks then wiped, sanded or scraped down?

The linked video doesn't seem to work as video for me, it's just a few images that don't show the process of the image above. Brough was asked in a few posts how she does it but didn't answer. Doesn't look like a subtractive process. Perhaps slip trailing done on paper then pressed against the inside of the mold then the white porcelain poured in? Just a guess. I'm sure she spent a lot of work to achieve success with her process.

Just to add another thing, I wouldn't put the platters/plates on the very top or bottom shelves, temps are more even in the middle section of kilns.

Hi Marie and welcome to the forum! It is possible to gently dab on a thin coat of brushing glaze with a sponge onto unfired underglazes then once that has dried apply subsequent coats with a brush but you do run the risk of smudging the underglaze. The other reason it's a good idea to bisque fire the underglaze on is underglazes contain binders that can inhibit the glaze absorption, by bisque firing it prior to glazing the binders are burned off. I have found some underglazes actually have enough flux in them to start glossing over at cone 04 so if you haven't used these underglazes and glaze together before I would do some test tiles to see how compatible they are.

Hi Naomi and welcome to the forum! There are quite a few variables that will come into play here. We don't know what is in the clear gloss glaze nor how fluid it is. Does the manganese wash just contain manganese or are there other materials in it? Which oxides would be applied under/over it? Just like with glaze testing it would be best to do some test tiles and see what interactions occur.

@Tbeans, have you tested the clay and found it is short?

After having a colossal waste of both time and money trying clay from a couple different manufacturers this year (that I haven't used much before) and getting crap clay that included bits of metal in one line and contaminated materials in another I went back to my original supplier and my tried and true smooth white(ish) clay. First and foremost is having trust in the quality control of the clay supply I use. Tony Hansen is the clay tech for Plainsman, I have used their clays for many years and happily went back to using it after this brief foray into other suppliers, can't afford this frustration again. Second I want a claybody that has an absorption of under 1.5% for the majority of my functional work. (I check the absorption figures myself every 6 months or so) It's a plus if the clay is nice and soft when I purchase it so I try not to buy it if the suppliers stock is running low and it's older inventory they have on hand.

I'm going to move this over to "Ceramic Events of Interest", might get more eyes on it there.

What Kelly is referencing is available to see in a Google book preview here. Have a look at crack "F". Highly recommend this book! https://books.google.ca/books?id=TApnGTVLwxAC&pg=PA86&lpg=PA86&dq=hamer+and+hamer+cracks&source=bl&ots=inS6KQPb4N&sig=ACfU3U3-WW9HznLwIEytHMyGanL2bpymZA&hl=en&sa=X&ved=2ahUKEwiG1JCB0KPgAhWyPH0KHX7EBo4Q6AEwB3oECAcQAQ#v=onepage&q=hamer and hamer cracks&f=false

Hi and welcome to the forum! In theory there could be lead contamination in some materials, zinc oxide for example. Lead swab tests can have false positives and false negatives, how many swabs did you do? Was it a kiln brick you swabbed or a glaze? If it's a glaze a more accurate testing method would be to send a sample in for lab testing. One such place is BSC Labs, I've used them a few times, cost is approx $35 for one oxide then each additional oxide is an extra smaller cost.

Yeah, no, pottery plaster will break down in a kiln firing. Would be better to make a clay form and use that after bisque firing it.

I wonder why they didn't suggest a floc? edit: I found the cation exchange rate for 6Tile, it's 9.8 so in theory it will not deflocculate nearly as easily as EPK.

So you would be firing the plaster mold to glass slumping temps?

If you do suspect something is mislabelled it would be a good idea to try and figure out what is actually in the bag. David Hewitt and Mike Bailey wrote an article on trying to solve the mystery of what's inside unlabelled bags and buckets, it's a good article, might help. Firing a small amount of the material in either a tiny bowl or a depression in a slab of clay is a good start. Try about a 1/2 tsp from the bag of what you think is Gerstley Borate, see if you get a puddle of melted pale tan coloured crazed "glaze" at bisque temps.

Metric weight for glazes, always. Pounds and ounces for clay for throwing. I live in Canada and use a mishmash of metric and imperial in daily life, metric is so much more logical.

@Emily Z and @Carrie N, try sending the op a pm as she hasn't been on the forum since making her post here. She will get an email letting her know she has a message. (to send a pm click on @Susan Speck avatar or name then hit the little envelope icon at the top of her page and follow the links)

Do you need help with your post?

@NancyE, sorry for the late reply, I was away for a bit. Since the beginning of this year I've had problems with 2 different claybodies from 2 different manufacturers. First issue was bits of metal in the clay which doesn't sound like your issue. Second problem was with a claybody that included small chunks of rock which sounds like it might be the same issue you are finding. This clay was from Tacoma Clay Art Center and the clay tech and I had several productive emails back and forth about it. Image below of a couple of the small chunks of rock I dug out of the clay. Is this similar to what you found? Rae (clay tech at Tacoma Clay Art Center) and I both ran sieve tests on it and found chunks like this. Rae let me know they are having troubles with all their claybodies that contain Lincoln 60, to the point that they are running QC tests on all the new batches of it. She ran samples through a 60 mesh sieve and 4% of it didn't pass through. I would ask Aardvark if the Black Mountain contains Lincoln 60, might be a place to start.