[Clay slips over clay bodies with different shrinkage rates?]

@Joseph Firebornthank you!

[Clay slips over clay bodies with different shrinkage rates?]

4 minutes ago, Joseph Fireborn said:

Mostly things to change the viscosity for brushing and some flux to make the slip adhere better to the greenware underneath after firing.

Would you mind going into some detail? And have you found that any of the additions affected the glazes? 

[Organic Clay Textures]

On 3/22/2023 at 4:17 PM, Min said:

Yes, it does look like the artist applied a thick extremely sandy or groggy slip to the piece. I would suggest adding sand or grog to slip made from the same clay and applying it as soon as possible to the damp pot.

Hi Min, when you refer to sand, is that silica? Or any type of sand?

[Clay slips over clay bodies with different shrinkage rates?]

12 hours ago, Joseph Fireborn said:

I make a slip out of a clay body that I dry and then grind down into a powder form so I can mix it with other additives. All of my work uses this slip over another clay body.

I love slipping pots this way, it adds a lot to the final form if done right. I am not sure exactly what you are after, but the best thing to do is try applying you slip to different stages of the green ware in the drying process. Find which one you get the best results with for what you are after, and then repeat that process a few times before committing it it.

That's a great idea to experiment with different stages of greenware. I'm curious - what additives do you add to your clay powder? 

[Clay slips over clay bodies with different shrinkage rates?]

Is it ok to apply a clay slip over another clay body that  have different shrinkage rates? For example, I'd like to apply Standard 710 with a shrinkage rate of 11.5%, over a sculpture made of Standard 420 with a shrinkage rate of 10%. Are the shrinkage rates close enough that I won't have cracking or other issues?  It would be a thin coat, just enough to change the color.

At what point will the differences in shrinkage rates cause problems? I'm assuming the greater the difference, the more likely it would be to have problem.

Should I add anything to the slip to improve brushability? (That wouldn't affect the glazes.) I'm doing this because I love how glazes look on 710 but 420 is better for building.

I fire to cone 5.5 in oxidation if that makes any difference.

thank you!

[low fired stoneware vs mid fired]

1 hour ago, Callie Beller Diesel said:

It should also be mentioned that there’s a narrower window where nice looking and well melted, well fitted glazes overlap at lowfire than at cone 6 or cone 10.  The lower you go, the better versed in ceramic tech you need to be to get it to work. You won’t do it just out of the box with commercially made materials. 

This is something I find really frustrating about ceramics. I come from a background in painting, so it's been a major shift in working methods and especially my attitude towards these technical demands. It's overwhelming at times. I realize there's no shortcut. Sorry, just venting. I do appreciate the technical expertise offered here and have learned some very important tips that have made a huge difference!

[low fired stoneware vs mid fired]

2 hours ago, neilestrick said:

Keep in mind that Pinnell's test was just one of several different types of tests that could be done to determine the strength of clay, and that most clay bodies are plenty strong for what we do with them. If strength was really an issue then we'd all be using low fire red clay, yet it's one of the least used bodies there is among ceramic artists. And although grog weakens bodies, it's still used in a large percentage of stoneware bodies because it has other benefits and doesn't weaken it enough to matter. Pinnell's tests are incredibly interesting and the results surprised most of us, but they're more academic than practical for the typical potter. The far bigger issues when determining the strength of a piece are the form, thickness, and construction technique. Little fingers on a figurative sculpture are going to be easy to break off regardless of what type of clay body you use. We select clay bodies based on firing temp, texture, and color, not MOR test results.

Very good points. I'm probably not a 'typical' ceramic artist in that my goals run counter to what most people want (some of the time), especially in terms of glaze. But I'm attracted to low fire clay because of less warping and distorting of forms. And the practical advantages of less wear and tear on my kiln. However, my patience for endless experimenting is limited, so I'll have to take that into account too!

[low fired stoneware vs mid fired]

Thank you, everyone, for your helpful replies. I think i'll experiment with earthenware and see how that goes. 

[low fired stoneware vs mid fired]

On 4/13/2023 at 1:40 PM, Jeff Longtin said:

Hey Kakes,

The first thing to mention is your terminology.  Typically stoneware clay is not considered "low-fire". It used to be considered "high-fire" (fired to cone 10) but more recently many bodies have been mixed to vitrify at a "mid-fire" temperature. (cone 6) 

Earthenware clay is more typically considered "low-fire". ( fired to cone 06) The two local companies, Minnesota Clay and Continental Clay, both sell earthenware clay but I know several potters who like to fire their earthenware pots to cone 2.

In a sense any vitrified clay is highly durable. In my experience, however, earthenware tends to be a bit more brittle than stoneware or porcelain clay, after firing.

As to which is best, that, I think, would be more about color range you want to work with. If you're finishing the pieces in glaze earthenware temps give you brighter colors and a broader color range.

Hope this helps?

 

Thank you - very helpful! I'd like to experiment with earthenware clay fired to 04. It feels a bit daunting because I'll need to find a different set of glazes.

[low fired stoneware vs mid fired]

On 4/13/2023 at 1:03 PM, Callie Beller Diesel said:

If you’re concerned about the fragility of a sculpture as opposed to a pot, how the piece is constructed is going to have more of a bearing on the durability than the clay body. A thin walled piece constructed with the best methods described in Min’s link above will still break sooner than a brick made using the exact opposite principles. If your sculptures are thin walled and unglazed, making them out of earthenware glazed with a well fitted glaze will add strength, but you’ll still need a lot of packing padding. If your pieces are solid, they’ll withstand more impact. But even construction bricks break if they’re dropped from enough height.

That's exactly my situation - I make thin walled slab built pieces with a lot of unprotected edges. Thanks for this info - i need to investigate the type of glazes I like to see if they fit. 

[low fired stoneware vs mid fired]

On 4/13/2023 at 12:13 PM, Min said:

Pete Pinnell did a test of claybody types many years back and one of the things they tested for was modulus of rupture, don't know how relevant that would be to your question although it's an interesting read. Link here to it. I would hazard a guess that how you pack and ship your sculptures might be more germain.  

Sorry your question didn't elicit any responses in the chem section.

Thank you for this link - fascinating! I'm surprised that grog weakens clay and that red earthenware fired to 04 is the strongest. Do you think MOR would also indicate chipping resistance?

[low fired stoneware vs mid fired]

Hi everyone, I posted this question in Clay and glaze chemistry and got no replies so I'm trying here. I hope that's ok.

Is there a difference in fragility and durability between vitrified low fired stoneware (04) and vitrified cone 6 stoneware?  I make non-functional sculptures so I'm primarily concerned with handling and shipping.  What would be the advantages or disadvantages of using either clay for sculpture?

thank you!

[Low fire vs mid fire for sculpture]

Hello, 

I was given some low fire (cone 04) Laguna stoneware. I normally use cone 6 stoneware (Standard) and all my work is nonfunctional. My question is what is the difference in fragility and durability of the fired clay between the two types once they are vitrified? My sculpture involves slab building and sometimes has thin edges. My main concern would be shipping the work.

thank you!

[White raised bumps after glaze firing]

I've experienced raised bumps like you describe from what I assume is a clay/glaze mismatch. I use Standard 710 with Mayco alabster glaze (I think - will need to check on this when i'm at the studio. i'll check and will also take a photo) This doesn't happen if I use Standard 420 which is a very groggy sculpture clay. Go figure.

I don't have anything helpful to add. Since i don't make functional ware, i've just decided to use it for the bumps.

[Bubbles In Black Stoneware]

12 hours ago, Callie Beller Diesel said:

@Kakes Titi has her location (below her avatar) listed as Ecuador. She likely won’t have access to North American clay bodies. Most clay bodies are only available regionally, because they’re not very cost effective to ship, and is usually easier to dig up closer to home.

I was responding to the original poster. But yes, you're right about regional clay availability.

[Bubbles In Black Stoneware]

I use Standard 710 (which is 266 with grog), single fire on a Skutt automatic slow fire setting to cone 5 with a 20 minute hold, no bisque at all, and I haven't had any problems. (I sure hope I'm not jinxing myself saying this!) I use commercial glazes from Amaco, Spectrum, and Coyote and most glazes come out beautiful on this clay.  Since I never bisque, I'm wondering the bloating you have is from some other issue. Maybe you're firing too hot?