Press Mold Making

Special thanks to Josh Renaud, Insta @josheramics, for sharing what he has learned.

Soft vs hard object to be molded: not super important either way, it just needs to be firm and sturdy enough to not deform when the plaster is poured, when you press clay along seams to seal gaps so plaster won’t enter them, or when you remove clay or other material used to block plaster from subsequent stages of the mold. Whether a single-part or multi-part mold, the object stays put through the mold-making process until the plaster sets.

This is the best video I found for making multi-part press molds: https://youtu.be/Lo8C5LGjuys?is=JYbNRJqKIBGVspHb

  • At about 2:30 in that video, he demonstrates what I referred do by “pressing clay along seams to seal gaps.”

  • John Britt

  • Depending on the size of the mold and volume of plaster, we might need to wait a day between each pour to allow everything to chill before we start removing clay temporarily attached to it.

  • All of this of course depends on how detailed and precise your subject pot is.

I try to start with an object that is hard and solid, then only use plasticine to bring it to the final form I want. For example, I have a plastic container I found that is a nice shape and proportion for a bonsai pot, and will just add a slight rim to it using plasticine.

Note about using hollow objects like that: I fill them with clay or something else to keep them from deforming or releasing air bubbles when I pour the plaster.

It depends on many variables, so show me what you’re trying to mold or explain your idea a bit and maybe I can help a little more with it.

  • Plaster is relatively durable, once cured (this takes a week or more for a thicker mold), just don’t drop them or use hard tools. Make the walls 1-2” thick unless it’s a very small pot and you should be fine.

  • The clay color doesn’t actually transfer much. This would only be a concern if you’re using white clay and it’s really important to keep it clean, like with porcelain.

  • Single part mold only works if there is no texture or indentations that will lock the piece into the mold. And yes generally leave the feet off too. The pros (japan and elsewhere) have separate molds for feet they then attach to the body

Some videos I saw of a bonsai YouTuber who visited some great pot makers in tokoname and had really great info.

Here’s one from that series: https://youtu.be/pKwXwRmBvzg?is=F5fB7WakFtKxreuy

Michael Wei