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cstovin

Making slip from clay trimmings

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Hi all

ive been keeping my scraps and use them to make slip from.  It seems no matter how thick I leave it, I’m rarely successful at getting it dry enough to get it out of the mold?   It never seems to dry; I have no idea what I’m missing.  I tried adding a little sodium silicate to keep it mixed....any ideas?

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Hi cstovin!

I don't slipcast - that said - I do watch vids!

Are you using plaster molds? ...plaster absorbs moisture, which should firm up the slip closest to the mold.

Are you pouring out/back the slip some time after filling the mold? I'm seeing that molders are casting "hollow" pieces. The slip up against the mold, being stiff enough to resist flowing, stays in the mold; after pouring, the remainder has air on one side, plaster on the other - now wait for the casting to dry some more before splitting the mold! ...experience tells how long to wait before pouring, and how long to wait before splitting. Looks like thickness is about 5mm or so - not so thick as to split/crack, and not so thin as to break easily either. 

A quarter sized puddle of slip dries to leather hard on my plaster bat rather quickly, hmm... 

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You need to be more precise in the making of the slip. HERE is a good resource. Sodium silicate deflocculates the clay, meaning it makes it more fluid without adding more water. So you have a slip that is fluid enough t o pour in and out of the mold, but is low enough in water content that it will dry quicker and shrink less in the mold. Also make sure your mold is totally dry. If it is a newly made mold, it must be dried completely before using, which could take a week or more depending on conditions.

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On 8/4/2019 at 8:50 PM, Hulk said:

Hi cstovin!

I don't slipcast - that said - I do watch vids!

Are you using plaster molds? ...plaster absorbs moisture, which should firm up the slip closest to the mold.

Are you pouring out/back the slip some time after filling the mold? I'm seeing that molders are casting "hollow" pieces. The slip up against the mold, being stiff enough to resist flowing, stays in the mold; after pouring, the remainder has air on one side, plaster on the other - now wait for the casting to dry some more before splitting the mold! ...experience tells how long to wait before pouring, and how long to wait before splitting. Looks like thickness is about 5mm or so - not so thick as to split/crack, and not so thin as to break easily either. 

A quarter sized puddle of slip dries to leather hard on my plaster bat rather quickly, hmm... 

I’m waiting until the slip has dried enough to flip the mold over and it fall out; I’ve done this a lot before I did pottery, but the shavings from my pottery scraps just never seem to dry enough to get it out of the mold

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On 8/4/2019 at 10:20 PM, neilestrick said:

You need to be more precise in the making of the slip. HERE is a good resource. Sodium silicate deflocculates the clay, meaning it makes it more fluid without adding more water. So you have a slip that is fluid enough t o pour in and out of the mold, but is low enough in water content that it will dry quicker and shrink less in the mold. Also make sure your mold is totally dry. If it is a newly made mold, it must be dried completely before using, which could take a week or more depending on conditions.

Awesome thanks!!

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