I can remember, as a child, one of my most favorite toys (other than the ones that my dad hand made for me) and this was a wood-burning iron. I would heat the iron up and burn designs into any hardwood or plywood that I could get. The burn marks left a dark burn in the hardwood that drastically contrasted the color of the wood used. We did wood-burning a lot in cub scouts. Doors that have been glazed give this effect. Some doors are routed with small grooves that follow the design of the particular frame. Then the inside of those grooves are glazed with different colors of glaze, depending on the door finish. This gives the door a rich look and is very esthetic in appearance.