I usually use the same paraffin sealing wax that I mix into my bullet casting lube. Melt it, and apply a layer or two with a small brush. A tinner's acid brush works well for jobs like that. It gives a thin, durable layer that won't get displaced by whatever casting medium you use.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!