How to finish plates using plaster molds?

[Grace Jennings]

I have watched numerous videos where plates are being thrown using plaster molds but the videos always end as soon as the throwing is complete. I’m interested in learning about the steps necessary to finish plates. How long do they have to sit on the mold before pulling them off? What technique is used to remove the plate without warping or damaging it? I just purchased a power arm and plan to start making plates using my new jig and jolly. If I want to steadily make the same shape, how many duplicate molds do I need at any given time? 
 

Thank you in advance for your time!

[Callie Beller Diesel]

Hi Grace, and welcome to the forum!

The number of moulds you need is usually dictated by the number of plates you need to produce in a day. A jig/jolly is a time saving device for larger production amounts, so I’d say a minimum of 12. How long they need to be on the plaster can depend a bit on the condition of the mould, the water level in your clay, and the humidity, but I think I remember seeing something about 2-3 casts/day for more industrial operations. I think it’s more for a RAM press. On a regular plaster or hydrocal they just release as they set up and start to shrink. You can just pop them off if they’re on a hump mould, or they should pull away from the walls if they’re in a slump.

[Grace Jennings]

Thank you Callie! I always thought they would crack if left on a hump mold so I’ll just be more patient next time around 

[Callie Beller Diesel]

They will if you let them dry too much. You’re waiting for them to set up enough to support themselves, not letting them linger on the bat.