Talk to a representative at your local reclaimed-wood center. There are many places nationwide to find reclaimed lumber. Search for one online. Ask the center's representative for a piece to make a reclaimed-wood carving block. He will lead you to a piece of hardwood. Birch or walnut species make great carving blocks. These types of wood are rich in color, durable and water resistant. You piece should be about 16 inches long by 12 inches wide and 1 to 2 inches thick.
Clean your piece of wood well with soap and water. Let it dry.
Trim the piece down so that it is flat on all six sides. If your piece is irregular in shape, cut off the excess to make it rectangular. On a workbench, use a hand saw to trim the excess off your block. You can use power tools, but this project is small so hand tools work well. Use a hand saw to remove large portions. Remove the rough texture made from the saw with a hand plane.
Sand down the carving block on all sides. Round the edges. Sometimes it may be helpful to use a wood block wrapped in sand paper. Use a medium-grit sandpaper.
Dust off the block. Apply a generous amount of mineral oil to the carving block with a rag. Wipe off the excess.