However most casting powders work really well eg dental plaster, hydrocal plasters or other casting plasters available from hardware shops. This mold uses 250grams or 9oz of ultracal 30 powder per art stone made. Mix the casting powder with water following the directions provided with the mixture. Wait approximately 6 hours or overnight.
This is the fun bit - turn out your art stone/rock. It comes out beautifully smooth allow to dry for a day or two.
So much joy painting it there's a downloadable data sheet on my website with all the art stone dimensions and mixing quantities. This item is made of silicone.