Clay Planet's custom Dry Casting Slip Formula.

Sold dry by the 50 lb sack. 

MIXING INSTRUCTIONS
For every 50 lb sack:

Mix with 2.5 gallons water

2 oz Sodium Silicate

1/2 oz Soda Ash (Sodium Carbonate)

Mix well - 3 hours,  Let sit overnight, remix, and test specific gravity.

Take a gravity reading. 1.75 is your target. Anything between 1.7 and 1.8 is considered within a normal casting range.