Remove the cushion. If it is attached to the chair, use a seam ripper to cut through the threads that hold it to the chair.
Mark the location of the tufts on the cushion with tailor's chalk. All tufts should be at least 3 inches from the edge of the cushion.
Stick a pin into each chalk mark and press it straight back through the cushion. Mark the point where the pin comes out on the back with another chalk mark.
Thread a needle with 36 inches of upholstery thread. Knot the ends of the thread together. Fold a 1-inch square of muslin in quarters, thread the needle through the center of the folded square and pull it down to the knot. The small piece of fabric will keep the thread from pulling through.
Run the needle all the way through the cushion, going in through one of the chalk marks on the back and coming out at the corresponding mark on the front. Pull the thread tight.
Thread a shank button onto the thread and run the needle back through the cushion at the same point. Thread the needle back through the cushion and the button three more times. Finish by knotting the thread close to the fabric in the back of the cushion and cut off the excess thread.
Make tufts at the other chalk marks in the same way.
Reattach the cushion, if required, by hand-sewing it with a needle and upholstery thread.