Place goggles on and clean clay flower pots in soapy water. Let dry and sand away any rough edges on the pots.
Place 20-inch clay flowerpot on flat surface and add the 18-inch pot on top. Stack the 16-inch clay flowerpot on top of the 18 inch pot. Draw a line all the way around with a pencil where the rim of the 18-inch pot touches the 20-inch pot. Repeat with the 16-inch pot.
Paint with the chosen color only to 1 inch above the penciled line. Let dry and repeat the process three more times. Add decorations such as additional paint, stickers, mosaic tile or use stencils to create a pattern on the pots.
Seal all the pots on the outside with a water-based polyurethane. Let dry and repeat the process two more times.
Move the pots to where the pedestal will be placed. Place the 20-inch pot open-end down on a flat surface and run a bead of construction adhesive around the rim of the 18-inch pot. Place the 18-inch pot rim-first on top of the 20-inch pot. Repeat with the 16-inch pot. Let dry 24 hours before placing anything on top of the pedestal.