Chalk printer

Restaurants, pubs and bars are still making good use of that old fashioned technology: blackboards and chalk. I was thinking about how it might be possible to "print" onto a blackboard using chalk.

The setup would probably be a flatbed printer, with a printing mechanism like the felt tip printer. Obviously a large flatbed would be ideal to account for different sizes of chalk boards.

Colour could either be delivered using different coloured chalks, or perhaps through combinations of primary colours (or would it be CMY?).

The advantages of this is are: the reusability - a display that can be wiped clean and reused; the end product is cheap enought to be left outside (unlike LCDs or eInk displays); the display doesn't require power; easier to produce high impact designs over hand drawing (for those without such a skills set).