Sculpting with 2 different clay bodies, can it be done?

[kirstenrose]

I am looking to use 2 different clay bodies in my work.  I am not marbalizing. I would like to create a slab base with the brown clay and attach details and forms made out of the white clay using a slip that would be made from a mixture of the 2 clay bodies. I am also hoping to wedge the 2 clay bodies together and sculpt forms as well. Obviously I would test these things out but I was wondering if someone more educated on clay bodies could tell me if  both clay bodies have a shrinkage rate of 13% at cone 6, do you think this sounds like it might work? What troubles might I encounter if I do decide to try this? 

 

[Pres]

I have often used two different clays to create pieces. I would use a white clay for horns on an object, or borders on a pot added on. In the long run it requires that the two clays be mature at the same temp, and that they have a similar shrinkage rate. You can see how if a clay body does not shrink the same as the clay it is attached to that there would be separation of the two pieces. At the same time if they do not fire to the same maturity temperature, taking glaze, or other surface treatments.

 

best,

Pres

[neilestrick]

Yes, as long as they have the same shrinkage rate they should work.

[glazenerd]

Pres and Neil are both correct; some additional fine points.

1. Use two stoneware or two porcelain bodies: porcelain dries at an accelerated rate in comparison to stoneware. Attachments made of porcelain for example would dry at almost twice the rate of the stoneware body: cracking would likely occur.

2. Dark or red bodies clays have higher iron, sulfide, and carbon content. If you used a white stoneware body; the firing schedule would still need to follow the slow ramp to ensure carbon burn out. (1250-1750F)  You should also expect noticeable differences in color shifts from the same glaze when applied to high iron bodies in comparison to white bodies. Nothing technically wrong with that, just a heads up.

3.  Shrinkage and cone ratings as mentioned; but consider COE of each body as well. If both are stoneware, there will be little appreciable differences in COE. There can be wide differences between stoneware and porcelain: some greater than 20%. The core issue being if your glaze works fine on the lower COE body, it might craze on a higher rated body. Again, if both bodies are stoneware: this is almost a non-issue.

There are techniques floating around about blending multiple bodies for effect: I do it all the time. You can wire cut off the slab and stack in layers to produce mottling. You can cut off larger cubes and stack to produce larger veins of color. How thick, how long, and how wide you cut pieces, and how you stack them all effect the variegation of color produced. Have fun, experiment, and enjoy. Pics of final outcome posted later would be nice also.

Tom

[Magnolia Mud Research]

9 hours ago, kirstenrose said:

I am looking to use 2 different clay bodies in my work.  I am not marbalizing. I would like to create a slab base with the brown clay and attach details and forms made out of the white clay using a slip that would be made from a mixture of the 2 clay bodies. I am also hoping to wedge the 2 clay bodies together and sculpt forms as well. Obviously I would test these things out but I was wondering if someone more educated on clay bodies could tell me if  both clay bodies have a shrinkage rate of 13% at cone 6, do you think this sounds like it might work? What troubles might I encounter if I do decide to try this? 

Based on your statement of two cone 6 clay bodies each with 13% shrinkage and joined with slip made from equal amounts of both clay bodies, I would not have any more concern with the project than one using a single clay body.  I often join different clay bodies with the technique you described, including porcelain to stoneware with large iron content.  Test the strength of your joining techniques on ware other than your final sculpture to be sure both the clay body and the joining techniques will be reliable.   For some of my multi-clay body projects, I used a gradient of both clay bodies over a centimeter or more to mitigate the known differences in the shrinkage rates.  

.. 

My recommendation is to thoroughly think through the sculpture from a structural point of view and if possible use one clay body for the load bearing and supporting components.  Where the sculpture will have high stress points, make test pieces to be sure that the clay body joins will be adequate.  

LT

 

[Benzine]

What about using colorants to a body, to make the different colors?  How much does that affect shrinkage COE and such?

[Denice]

I have mixed, wedged, handbuilt  and thrown  C6 clays with the same shrinkage rate and have never had any problems.    Denice

[yappystudent]

I've fiddled around with the same techniques mentioned and have yet to have anything separate or crack based on clay body differences. Following good practices about being sure your stuff dries slowly and evenly might be why as I'm usually pretty careful about that. 

Don't forget you can just slip-paint over your main clay body and it will look exactly the same as if you've added a solid piece. Not sure what you're doing without images or if this would work for you. I've slip painted ^6 porcelain over ^6 stoneware a few times now and so far no issues. Why slip works better than just adding a piece of contrasting color clay I don't know, I don't even know if it really does. But I do know a block of the nicest porcelain my shop sells is about $9 more than the cheapest stoneware, so slip coating suits me. 

[kirstenrose]

Thank you everyone for your insights and suggestions. I purchased my 2 clay bodies and I will begin testing and exploring  I also purchased a few mason stains to play around with. I am so excited to get started! 

I will do my best to post some photos on this process as it unfolds