The folks at House Beautiful magazine said «to maintain the patina, they're rewaxed about every two months.» (theletteredcottage.net)
I now use Autentico chalk paint which was do much better to apply, and wax but realise that it would need rewaxing at some stage. (canarystreetcrafts.com)
Meant to last for eons, if you send it back for rewaxing now and again. (amidprivilege.com)