BCS parting dust (formerly PD-1) is a professional grade parting dust for use with both naturally bonded (clay) and oil bonded (Petro-Bondâ„¢) sands. It is manufactured by Asbury Graphite, Inc., and sold to foundries under the trade name "Diamond Parting #4106â„¢". This parting is (almost) silica free. It is a mixture of porous minerals which have been finely ground. It has been formulated to be highly lubricious (marketing talk... means slick) which aids separation of cope / drag halves and pattern removal . This parting will not water proof the sand surface, so steam and gas can escape from the melted metal. This helps reduce surface porosity.
Parting dust coats the surface of a pattern so that the molding sand will not stick to it. This allows the pattern to be drawn from the sand and leave a clean, sharp impression behind.
Parting dust also coats the sand mating surfaces of the flask so the top half (the "cope") and the bottom half (the "drag") don't stick together. This allows the halves to be separated and the pattern removed. This separation line is called the "parting line" thus comes the name of this material: "parting dust".
Simply load half a cup into an old white sock and you have a handy duster. Apply a fine dusting to parting surfaces of sand mold and patterns. New patterns will benefit from thoroughly applying a coating of parting dust prior to first time use.
Keep the sock and unused parting dust in a tightly sealed can to avoid moisture absorption. (I use an old coffee can!). I figure I use about a tablespoon per mold. At that rate 5 pounds will last a long time!