Pyrography, or "writing with fire" is a technique used to burn artwork in leather, wood, and bone using specialized tools and, in some cases, torches.
The surface isn't limited to a stock piece of wood - just look at these examples.
The pieces shown are available for purchase (send a message for sizes and prices), but are shown mostly to give an example of what can be done. Large or small, if it's made of wood, leather, or bone, it can be burned on.
Original artwork, or custom images at your request.