Place the 1-by-12-by-70 1/2-inch planks vertically oriented and parallel to each other on a work surface with the 1-by-70 1/2-inch edges resting flat. Space the outside sides of the boards 24 inches apart. These are the sides.
Position one 1-by-12-by-24-inch plank across to top and bottom ends of the sides. These are the top and bottom boards.
Place the 1-by-12-by-22 1/2-inch boards between the sides. These are the shelf boards. Position one board 12 inches up from the bottom, a second board 24 inches up from the bottom and the third board 48 inches up from the bottom.
Drive decorative head screws through the top and bottom boards into the ends of the sides every 2 inches with a screw gun. Drive decorative head screws through the sides into the ends of the shelf boards every 2 inches.
Stand the shelving unit upright. Brush two even coats of shellac over the assembly using a natural bristle paintbrush. Allow the shellac to dry 24 hours between coats. Wait 48 hours after the final coat before using the shelving.