How to Make One:
http://www.overgrow.com/growfaq/?qa=1376

How it works:
The resin glands are heated to a temperature which allows THC to vaporize, yet does not burn the material. The THC vapor is inhaled, and carries no carcinogens, so it is 100% healthy.
In the case of the light bulb, a lighter is held to the bottom making the glass adequately hot to vaporize the weed, but not burn it. You get THC vapor, the carcinogenic material stays behind.

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