What is the Best Wax for Sealing a Corked Bottle?

Why do you want to seal a corked bottle would be my first question and the second would be what the container holds. If the container holds a liquid simply invert the bottle occasionally to keep the cork swollen. If the container holds anything else please keep in mind allowing room for expansion.

I think what you want is the wax used for sealing letters with a stamp. It comes in flattish small candles and is hard and shiny when it dries. You'd find it in stationery stores or google 'sealing wax'. The other non-brittle wax is beeswax. Quilters use it to straighten thread (quilt shops) or go to the source and contact a beekeeper. It really does come from bees. Candles are sometimes made from it, but it's more pliable than candle wax and wouldn't be as hard when on the bottle.