Tips for making a good slip mold

[dom92]

Do the experts here have any sage advice on the best plaster materials to use for making a good slip casting mold?  Until now I've used a wide variety of commercially produced slip casting molds and they've all been excellent in quality and construction.  Nice rounded edges and very durable.  I've even dropped a few here and there and all they did was leave a dent in my vinyl floor.  

Anyway, this weekend I wanted to take a shot at making my own slip casting mold using plain old plaster of paris bought from the local hardware store.  It "works," but I can already tell this won't hold up for long.  One drop, even to countertop level, and it'll probably explode in to a dozen pieces.  I'm thinking this primarily due to the type of plaster I used to make it.  Do the commercially produced molds use a different kind of plaster?  I do have a bag of jewelry casting investment (which is primarily POP), and I was thinking of giving that a try as I know from experience how smooth and durable it is.  I just don't know if it will absorb water from slip properly.  

[Fred Sweet]

dom02-

Your best material is #1 Pottery Plaster from USG. 

https://www.usg.com/content/usgcom/en/products-solutions/products/industrial-and-specialty/ceramics/usg-no-1-pottery-plaster.html

Use their data sheet for mixing instructions located at the bottom of the link above.

Regards,

Fred

[dom92]

Thanks, Fred!  I should have guessed that there was a special mix out there.  I'll give it a try!  

[oldlady]

try not to drop the mold.  it could bounce onto your toe.

[Mark C.]

(Your best material is #1 Pottery Plaster from USG. 

https://www.usg.com/content/usgcom/en/products-solutions/products/industrial-and-specialty/ceramics/usg-no-1-pottery-plaster.html

Use their data sheet for mixing instructions located at the bottom of the link above.)

Fred is spot on.This is the best for molds.