Heating in the oven changes the color, there is a name for this, and it enhances the potency for about 5 hours or so. This is what I am told. I use a vaporizer, set it at 250 degrees, attach a vacuum pump to the glass in place of the whip, pack herb in the glass tube semi tight, using a wooden dowel. I keep the herb back from the heater end of the glass tube, 1/2 to 3/4 inch to prevent the herb from igniting. I turn the vacuum pump on, run it until the glass reaches around 120 to 130 degrees. Keep an eye on the herb if you go to 130 degrees, this is close to the point of ignition, but going here gets all the potency out. At this point the herb is dry and hard inside the glass tube. It has also changed color. Now I don't know about the five hour thing, but my herb has gone through this process and is potent for weeks after I vaporized it. The darker the green the herb is the more potent it is with this process. I have been to Vietnam smoked real Thai stick, and this process has taken me as close to Thai as I have ever come before. Try it it works wonders. This process will make great hash, you can crumble the herb to a dust with your fingers, or leave as it is when you pick it out of the glass tube. I use a stainless steel knitting needle, to pick and push the herb out of the glass after my process.
I forgot to mention my friends call me Mr. Vapor see another vapor I created. You Tube, White Gasoline Vapor, by iambillythekid. Read everything.