Using slip for texture

[Gabby]

In the article I read today on the daily blog, https://ceramicartsnetwork.org/daily/pottery-making-techniques/ceramic-decorating-techniques/the-icing-on-the-pot-pottery-slip-decoration-that-creates-texture/, the author shows a very intriguing process for using slip at the leather-hard stage to get interesting texture.

Can you give me any advice on how to prepare the slip for this? Like how many parts clay to water so that it won't run but won't crack?

Could I use a porcelain slip on a red stoneware pot?

[C.Banks]

DEFLOCCULATED SLIP FOR DECORATION by Matthew McGovern

[preeta]

Porcelain slip on dark claybody is exactly what I love using.  However cracks are about two clays shrinking differently. To get the raised effect in slip trailing I use as C Banks posted  a defloculated slip or even casting slip (I add ball clay to thicken the casting slip so it won’t run when I am drawing lines with a hair dye bottle). 

Since the two bodies are not a good match I have to experiment a bit to see what leather hard or wet stage my claybody needs to be.  For lines and dots I put the slip on immediately after throwing and then cover and slow dry. 

I do love cracks though when I slap on slip so I tend to use that on bone dry greenware or almost bone dry to get a variety of cracks. 

[Gabby]

Thank you, CBanks and Preeta for these very useful answers. I had never heard of deflocculant and will look it up right away.

[oldlady]

gabby, it is much easier to use your own clay body to make the slip whether you defloc it or not.   if it is too coarse, you can sieve out the sandy stuff to make a smooth slip that is easier to work with when you apply it to your pot.   you do not have to use a fine sieve, 40 or 60 is enough. 

 it is fun to do this and i hope you enjoy the technique.

[Callie Beller Diesel]

In my own work I use a lot of white slip over a red clay body. I work at cone 6, and I found that if you're trying to avoid cracking, a white stoneware actually has better compatibility with my red stoneware than a porcelain over the same.  

I work with Plainsman clays, so I was easily able to go on their website and find information about shrinkage rates and COE, and find numbers that were close to each other. My main clay body is M390, and I use M370 as a slip. There is actually a formulation for a white slip that matches the m390 shrinkage exactly, but I'd have to make it myself rather than just buy a 50 lb dry bag and add water, but my current method works and I am lazy.

I reclaim my clay, so for texture work I tend to avoid the use of Darvan or other deflocculants. (I do use a deflocculated slip if I want a smooth liner on the inside of a mug, but I don't usually screw too many of those up.) If you're not using deflocculated slip to lessen the water content and a therefore the shrinkage, you need to really be aware of the optimum times to apply your slip, and work within that. If you let your base piece get too dry, scrap it and try again rather than trying to resurrect it. The two clays need to shrink together. If your base piece is too wet, rehydration can be an issue, and cause a piece to collapse. Different clay bodies will rehydrate at different rates, so if you're going to play around with this technique, allow yourself some time to get the right feel for your material. 

[Joe_L]

Applying slip makes my acne worse!

I'm assuming the slip is making it harder for the underlying body to off-gas properly .  This is single fired on a coarse iron-rich stoneware to ^9.  TBH the body is underfired and this glaze is pinholing slightly where there is no slip but I wanted to show you the slip makes the problem worse.

[Callie Beller Diesel]

@Joe_L I bisque, and I don't have this happen. Perhaps you need a bit of a soak in the temperature zones where your glazes and clay are off-gassing on the way up. It sounds like the heat just needs more time to work. 

[Joe_L]

Very likely.  I'm slowing in the 600-900C zone for burn-off, and then again doing Nerd's slow final climb to top temperature. Will need to slow down further as introducing the white slip has worsened the problem. I thought it would be a useful picture even for people who aren't single firing as an example of the slip changing the game.  The slip is a white stoneware body Scarva white decorating slip that doesn't pinhole in itself I haven't seen pinhole on other bodies I use under single firing, but it promotes it on the buff body.