best agent to release clay from plaster, when clay will be reused.

[s6x]

looking for release agent to separate clay from a plaster mold.  I'm not doing slip casting. I'm pressing regular clay into a plaster mold to get a certain shape.   Cooking oil, WD-40 and lubes have been recommended, but  I often reuse my clay when whatever I'm creating doesn't work out.  Will cooking oils and lubes in the clay interfere with the clay's "reusability"?   If so, what is a release agent that won't interfere with the clay's integrity? Thank you!

Edited October 6, 2023 by s6x

[LinR]

Place a piece of cotton on the plaster slab, then your clay for recycling on that.  You still get the water absorbed by the plaster without the clay coming in contact with the plaster.  Lin

[s6x]

13 hours ago, LinR said:

Place a piece of cotton on the plaster slab, then your clay for recycling on that.  You still get the water absorbed by the plaster without the clay coming in contact with the plaster.  Lin

oh, sorry!  I  just realized how unclear my question was!  The plaster in this case is a plaster mold.   I'm pressing clay into a plaster mold to get a specific shape, but then I want to release the clay so I can continue working on it.  

Edited October 6, 2023 by s6x

[neilestrick]

The plaster itself should dry the surface of the clay enough that it will release. If it's not releasing quickly enough, then dust some corn starch on the mold or the clay before pressing it. I would not use any sort of liquid on the plaster, as it will just soak in and ruin the porosity of the plaster.

[Chilly]

If it's not releasing easily, try drying the plaster more.  Put in a draughty place, not a hot one.

[Denice]

 When I make a plaster mold I smooth up the out side edges of the mold and check for and under cuts that might need to be blended in.  I give it a thorough wash and set it in front of a fan to dry.   I would throw away  your clay used in test pressing,   a small piece of plaster will contaminate your clay.   You could have cracks and small blow outs  from plaster in the clay   during a firing.  Larger molds  I pour the plaster outside where I don't have to worry about splatters of plaster.   I can control the mess of smaller molds in my studio.   It is starting to cool here so I need to check my plaster slabs  and wash my slab roller canvas's.   Cleaning them on the driveway  and letting them dry there keeps them from getting creases.    My husbands loves to play with water so he will  take  on this job claiming that he just wants to help me.       Denice

[Jeff Longtin]

The kind of a mold you're pressing into and the clay you're using...are two factors that can affect your results.

Are you pressing into a deep three-dimensional mold or are you pressing into a shallow relief type of mold? 

Strangely, what I have found, is that pressing clay into a mold is not as simple as I previously thought. If the clay is too wet, it sticks, if the clay is too dry, it doesn't fill all the deep details as well. A little trial and error helps. Perhaps your clay is too wet. A little stiffer clay is harder to press but less likely to stick. 

The way you press the clay into the mold also could be a factor: are you simply using your fingers to press the clay? I've seen where people use mallets to really FORCE the clay into the mold. (This for shallow reliefs with lots of detail.)

Also, are you dropping a ball of clay into the mold and then pressing it from there? An alternative could be to roll out a slab of clay and then drape the clay slab into the mold. Doing it this way shortens the time the clay is in contact with the mold surface. 

The kind of clay being used also affects the process: a wheel throwing clay tends to be more plastic and friendly to manipulation, whereas a hand building clay might be more prone to cracking and less friendly to repeated pressing and pulling.