Have you ever experienced a leak in the heater core of your car? Ethylene glycol (automotive antifreeze) causes a subtle mist that forms a tenacious film on the interior of your windshield. You have to use Windex to clean it.
A couple of weeks ago, I was sent a supply of un-flavored, commercial Black Cavendish. It was truly black, and squishy. Not a chance of mold, because of the polypropylene glycol (PPG) it contained. It turns out that it is black only because it stays "wet".
I packed a pipe with the black Cavendish, allowed it to "dry" for a few hours, then lit it up. It was mild and pleasant, though a bit uninteresting.
I spread a bunch into a foil pan, then slowly heated it in a toaster over set to "warm". This is about 220°F. At first, I thought some of it had ignited within the toaster over, because of a prolific cloud of smoke that began to pour out of the toaster oven. The "smoke" turned out to be simply the PPG outgassing. I continued this heating for about an hour. The result was a Cavendish that is uniformly, dull brown--just like all of my own Cavendish, once it has fully dried.
After this heating process, I had to use Windex to clean the exterior of my toaster oven of the tenacious film of PPG. (That on the interior was subsequently baked away with a much higher temperature.) Ahh! Like a leaking heater core in a car.
The now brown Cavendish smoked smoother, though still uninteresting on its own. But now I had something to use in blending--an ingredient with far less PPG, though some was still detectable. Of the two blends that I've made with this commercial brown Cavendish, both are rather nice to smoke, but always, always make my pipe gooey, requiring tedious cleaning--as though I had been smoking a commercial aromatic blend. But, I noticed that the presence of a little PPG increases the visible and palpable fullness of the smoke. That is, it produces a fuller cloud.
Another attribute of even this reduced PPG content is that the blend is more hygroscopic. That means that its container needs to keep atmospheric moisture out, rather than keeping it in.
These blends work considerably better in corncobs than in briar.
Bob