How to make Rochelle salt piezoelectric crystal

The ingredients that have worked for me for making Rochelle salt crystals are: 500 grams (1 lb) of baking soda (sodium bicarbonate, NaHCO3), available in the baking or spice sections of grocery stores 200 grams (7 oz) of cream of tartar (potassium bitartrate, KHC4H4O6), available in the spice section of grocery stores 250 milliliters (1 cup) of distilled water, available in grocery or drug stores (pharmacies), often used for cleaning contact lenses While baking soda is pretty cheap, $1.50 for a 500 gram box, cream of tartar is expensive, $5.00 for a 67 gram container.