These are dried out water-based markers. Turn them into liquid watercolor paint. Fill a clean baby food jar with water, tie about six dry markers with a rubber band, and set them in the top of the jar. I let them sit over night and watercolor is made!
All natural (mostly) wood stains! A handful of pennies in vinegar will produce a beautiful pale Caribbean blue stain. A wad of steel wool will give you a rich reddish hue. A combination of tea and a metal object in vinegar will produce a black stain.