Charcoal burning

Making charcoal in Heathfield - an experiment to find the biggest bit of wood I can successfully charcoal, results so far have been mixed. The biggest log of ash we used splintered into big chunks but doesn't make a very good mark. I think the Alder and Pussy willow are better mark makers. I have tried all sorts of wood to see which works better though its almost impossible to remember or recognise which is which after its burned!