I found this on Erowid...
http://www.erowid.org/experiences/exp.php?ID=31886
I have had vey successful results with this method. Start with 16 ounces of good quality, fresh salvia leaf, It should cost about $150 for this amount, anything less than this amount will be probably be lesser quality.
1. The leaf should be ground to the texture of cornmeal, and 1 ounce (28 grams) should be set aside in an airtight container.
2. Pour pure acetone (available at hardware stores) over the remaining leaf in a GLASS container, covering by at least 1/2 inches.
3. Soak for 24 hours, drain and reserve the liquid, and again pour enough acetone to cover the leaf by at least 1/2 inches.
4. Soak for another 24 hours and repeat step 3. after the last soaking, discard the spent leaf and combine the liquid from all three soakings.
5. Allow the Liquid to dry on a wide and flat surface, mixing in the ounce of reserved leaf when the liquid has reduced by half via evaporation.
6. once the mixture has completely dried, you should have one ounce of at least 15 times strength salvia, with one extra ounce added to ensure strength through possible loss of salvorin through short extractions, inferior salvia leaf, or exposure to heat.