Want to see the difference in woods, burn time, burn intensity and heat, explosive force try heating your house with wood for one winter. You can learn a lot about fire and fuel sources that way. Trying to melt crystals and turn them to glass I think would show it very well also.
Heated with wood for years and loved it. Would order a load of oak and ash every spring, cut, split and stacked it by hand well into summer, as well as harvesting some hickory and maple from my own property. The whole process teaches you a lot about wood. Some splits better green, some after it has dried a while. The really nasty twisted up knotty pieces went in the bonfire pile. Some had faces that I would bring out with my chainsaw and then finish up with chisels. My youngest son still has one in his room, it became his when he started talking to it as a baby, others went to friend's gardens.But back to the subject of fire:
Evergreens represent death, so I have used them to attract and speak to the dead, especially from graveyards, also, one mentor taught me to make incense from the dead flowers left on graves for the same purpose, all with the keeper's permission of course. Meditating on the flames from burning oak always seemed to give answers to difficult questions, while ash tended to be more useful for spellwork. Green hickory burns hot and throws off a lot of energy all at once. My father liked to burn apple in the fireplace when I was a kid, but I couldn't stand the smell, so I never experimented with it.
I almost always have something burning during workings, usually candles, because they interact with the atmosphere so well, though candle colors aren't all that important to me. And of course there is the ubiquitous little charcoal in the pot for herbs and incense. I also like those little oil lamps with the colored glass flues for really creating a mood altering atmosphere that is especially helpful when working with others.
Thinking about this has made me nostalgic for my old property and a big bonfire.