Here is an earlier post...
http://www.bbq-brethren.com/forum/showpost.php?p=3916459&postcount=9
The white smoke/blue smoke issue doesn't really occur with charcoal; it occurs with the added wood to charcoal for smoke flavoring.
When a fire stops flaming, it begins to smolder. At this point, combustion stops occurring in the flame, and begins occurring on the surface of the wood/charcoal. Less oxygen is required of the fire at this point. As long as there is enough oxygen and fuel being converted to heat, then this an ideal cooking heat source as the fire will be burning very clean.
At the point when the cooker begins to come up to temperature and the fire is stabilized, this will become the blue smoke state.
At the point where flaming stops and smoldering begins, there is too little oxygen for clean burning. I believe this to be the "white smoke" point.
You don't need a big piece of wood to get a good smoke, in fact, when it comes to making "thin blue smoke", bigger is NOT necessarily better. The key is to have small amounts of wood burn efficiently, so you get the sweet smoke flavor, and not a bitter, over-smoked flavor.
Dampened wood or cold wood on a fire can give off white smoke until the wood is heated and dry. This type of smoke is mostly moisture escaping from the wood and may not be from poor combustion. White smoke from poor combustion or from poor airflow in the smoker is heavy, smells overpowering, and it can cause that bitter acrid taste that everyone fears. Rule of thumb is to follow your sense of smell. Bad smoke is overpowering and smells bad.
Sweet blue can be seen even when it's "invisible" but you have to get the right angle of light on it. It's very thin, and wispy, and almost invisible.
follow your nose rather than your eyes. If you smell wood smoke, leave it alone, if you do not then add a few wood chunks, right on top of some red-hot coals, the best smoke is smelled, not seen.
