Sand the entire chair until smooth. Wipe away dust with a clean tack cloth.
Use a hammer and nails to add holes in the arms, seat and spindles of the chair to simulate worm holes in the wood.
Use a chain to beat the chair--to dent and mar it and simulate years of use.
Stain the chair with a rag; apply more stain to the areas of the dents and worm holes to define those marks. Wipe away any excess stain from the chair. After the stain has dried, sand it lightly and wipe away dust with a clean tack cloth. Apply a second coat of stain.
Sand the edges, arms and seat of the chair to reveal the wood and simulate wear. Wipe away the dust with a clean tack cloth.
Apply polyurethane sealant with a foam paintbrush to protect the chair. Allow the polyurethane to dry.