How to Make a Concave Semi Sphere Plaster Mold

Hand-building is easier when you have the right equipment in your studio. Slab building is easier when you have access to slump molds, allowing you to create easily transform a 2D slab into a 3D bowl.
Create your own concave slump mold using a Styrofoam ball and No.1 Pottery Plaster in this easy to follow step-by-step process.
Supplies Needed:
No.1 Pottery Plaster
Styrofoam Ball
2 Wooden Skewers
Flexible Casting Bowl
Murphy's Oil Soap
Plastic Mixing Bowl
Measuring Cup
Lukewarm Water
Metal Rib/Scraper
Plastic Table Cover

[@emilflognoid1532]

Thanks! Oil soap is a great idea for mold release!

[@Lisa-ek8we]

Thanks for this awesome how to!

[@jacquieblondin]

You’re welcome!

[@sandradebuyser3352]

Thank you for the great video! A little question, how can we prevent the styrofoam leaving marks in the mold? Thank you ❤

[@shondahill18]

I have found that you can't prevent the texture from being in the plaster mold. However, sanding the inside of the plaster mold works really well to make a smooth surface.

[@jacquieblondin]

I use a rounded metal rib on the inside of the mold and scrape it to get it smooth enough for my usage.

[@cyndanyia]

Why not make a giant batch in a large bowl and then pour what you need into your mold cup?

[@jacquieblondin]

Sometimes do make a large batch but you need other containers to be prepped for the extra plaster so you don’t waste any.

[@rusticagenerica]

What on Earth is Oil Soap . . . . . ??

[@jacquieblondin]

An oxymoron for ya! Great for wood floors too!