A word of warning – DON’T add too much resin at first, because it produces a LOT of smoke! Also if you use too much, the temperature of the charcoal can be reduced, and you can end up with a nasty-smelling cloud of steamy smoke (from the small amount of moisture always present in the resin). Start with no more than about 2 grams of resin – that’s approximately a quarter of a level teaspoonful.
Once that’s burned away and the smoke begins to thin out, add a small amount more. Don’t remove the ash unless it starts to smell bad. If it does, gently scrape it off with a spoon before adding more resin.
If the effect is too smoky for your taste, you can deliberately reduce the temperature by putting a small piece of kitchen foil between the charcoal and the resin – just one thickness is enough to slightly moderate the heat, and give a more “mellow”, less acrid fragrance. (This is a modern variation on the traditional Japanese method of heating incense on a thin sheet of mica over burning charcoal in the Koh Do ceremony – but kitchen foil is a lot easier to find than mica!) Don’t be afraid to experiment, to see what gives the effect you like best.