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making casts from fondant molds using pottery clay

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Is it possible to make decent clay castings with a fondant mold using  04 pottery clay?  The mold I have in mind doesn't have a lot of undercuts.  Could I just press the clay into the mold, allow it to get leather hard and then carefully extract it from the mold?  Thanks. 

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You will probably need a "release agent."  For plastic press moulds I use either talcum powder or WD40.  Both will prevent the clay from sticking to the mould.  You might need to remove the clay before it's leather hard, as by then it will start to shrink and can get caught.

I made a whole batch in one two hour class, dusting mould with talc, pressing the clay in, dropping it out, dusting mould with talc................. repeat

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On 3/13/2024 at 7:39 PM, MsBeth said:

The mold I have in mind doesn't have a lot of undercuts. 

@Chilly did you have any undercuts?...

PS Comparing fondant moulding with press moulding (probably the the closest pottery equivalent) ...

The fondant process:
— uses a flexible non-absorbent mould
— the fondant sets hard (without shrinking?)
— the set fondant doesn't adhere strongly to the mould?
— fondant sets strongly enough that peeling the flexible mould off undercuts doesn't damage them 

The press moulding process:
— uses a rigid and absorbent mould
— the clay shrinks and becomes harder as it dries
— minimal drying time needed/required
—— the mould absorbs water from the clay; so no air-drying needed and clay-mould adhesion is minimised
—— if the clay dries too much it will shrink-on any texture in the mould
— you cannot cleanly extract the (still fairly soft) casting if there are any undercuts.

So I suspect that you could have issues with
— air-drying the clay
— getting the clay firm enough
— clay shrinkage
— clay-mould adhesion
— the undercuts

PS Using paper-clay would probably strengthen the clay and speed air drying to some extent.


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 @MsBeth, for the fondant molds are you using flexible silicone molds? 

I think there is a bit of confusion with the terminology being used, when you say "clay castings" is seems like you are using casting slip. But then "press the clay into the mold" sounds like you are using pugged soft clay. 

I have used flexible silicone molds and soft clay, I very lightly wiped the molds with veg oil then pressed the clay in then flexed the mold enough to have the clay pop out. There was a bit of distortion with the molds with undercuts but it was easily fixed since the clay was soft. 

Dusting molds with cornstarch is also an option, don't have to be concerned with airborne silica with it.

Welcome to the forum.


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