The smoke coming from the chimney, can tell a lot about your stove. And it concerns not only its effectiveness, since everything is quite relative, and depends more on a variety of factors.
Generally, good performance is light (white) smoke coming out of the pipe. It would be better, of course, that there was no smoke at all. This would mean that the stove is operating normally and burns virtually all of what distinguishes wood kindling. But this effect should be to maintain a high temperature inside the furnace, and it is not always possible.
The efficiency of the furnace is measured at a temperature which is set therein. If it is high enough, it will burn everything, no matter what you have thrown into it. If insufficient temperature mode, a lot of unburned fly into the pipe in the truest sense of the expression.
If you saw that out of the chimney belching black smoke, you can be sure that the stove is not working efficiently, it emits into the environment a lot of unburned particles. The reason for such a deviation can be not only low-quality wood kindling, but, for example, excessive moisture content of wood.
If the degree of dryness of the wood is not sufficient (and then kindling altogether crude), the temperature control can be maintained in the furnace at an insufficient level, and hence, the stove will not burn completely kindling.
Yes, once again the cause of all disasters are too damp firewood. Poorly dried wood or dried does provide approximately 2-3 times less heat than enough dried. Moreover, such a kindling could harm the environment.
As an example, entertaining selection Pope (taken from "Norwegian Wood"). Since elections were held behind closed doors, to find out whether the cardinals were able to choose a new pope or not, people could smoke in color that went out of the pipe. For example, if a compromise was not reached, and the Cardinals were unable to decide on a candidate for this role, then poured out of the chimney black smoke. If the new pope has been chosen, it could be seen from the chimney white smoke.
In order to achieve the desired effect, added combusted securities a little more raw straw. Then the smoke became black and thick, and can be seen at a sufficiently safe distance. To achieve the opposite effect using a bundle of dried straw.
Incidentally, the picture shows how the kindling perfect combustion in the furnace. The fire inside the furnace is, and the smoke is not visible at all. Neither white nor black, nor of any other. So you can measure your oven according to the above example.