I started out from a square piece after watching a YouTube video by Kent Weakly of turnawoodbowl.com. He had an old piece of oak, and used carbonising as a way of adding some contrast, and also used the square shape as an "easy for beginners" lure. The bowl felt a little heavy, but was quite nice looking. I left the top face roughened by the chainsaw to provide further contrast with the smooth interior. After a few weeks some drying cracks started to develop as my poplar was only semi-seasoned unlike Kent's oak. I put the piece back on a large jam chuck made from a lump of ash, and turned the outside to a more conventional shape, then tidied up the interior. The wood has some quite attractive figuring from being near a branch junction.
Currently being exhibited in a local craft shop.
YouTube: carbonisedpoplar videoYouTube: carbonisedpoplar video