Clay slips over clay bodies with different shrinkage rates?

[Kakes]

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!

[Joseph Fireborn]

That is pretty close in rates I doubt it will matter. As with everything though, best to test before you commit to a ton of production work.

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.

[Kakes]

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? 

[Joseph Fireborn]

11 minutes ago, Kakes said:

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

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

[Kakes]

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? 

[Joseph Fireborn]

Just things like epsom salt and soda ash. As far as effecting the glazes for sure depending on the amount you add.

Edited April 24, 2023 by Joseph Fireborn

[Kakes]

@Joseph Firebornthank you!

[Pres]

I like to also use clay slip over pieces. I have found that when I assemble the chalices, that a coat of contrasting slip over top is a great way to accent further decoration after the slip dries enough. Then I use a potato peeler to facet the stems, and trimming tools to add incised bands into the stem and cup. These show up under glaze as lighter darker areas that add and extra layer of decoration. I like to have a lot of depth to my glazes where layers of transparency will reveal other things underneath.

The slips I use are SC 630 and SC 211Hazelnut.

 

best,

Pres

[Callie Beller Diesel]

@Kakes if you find your slip does wind up cracking over your clay body, in addition to timing the slip application right, you can create a slip with less water, but make it more fluid by adding a little darvan. I agree with Joseph that it might be close enough, but if you’re doing something with a thick slip it could make a difference.