High heat will bring more oils and tannins. It'll make your Nap look like dirty piss. You can clean it after you freeze precip and gently pour off the solvent, leaving your crystal stuck to the glass pan. Then, you can use Sodium Carbonate- baking soda put on a cookie sheet and into an oven at 150-170° for 30mins or so. Then, a cpl tblsp of powder into dirty naphtha and shake vigorously. Let it settle and watch it lighten in color. Shake it again, then add ice cold water, and shake one more time. Let it separate and pipette or syringe off the cleaned naptha.