Treatment for External wood furniture

Several coats of Rustin's Danish oil, a mixture of Tung oil with various other vegetable oils and resins, hardens to cure as an impenetrable soft sheen coating, which soaks into the wood and protecvts it from rain and weather damage. Rain simply beads on the surface. They recommend three coats for external woodwork - I err on the side of caution and apply five or six!
Tung oil has been used by the Chinese since the time of Confucius and is used extensively in boat (Junks)building as n effective preservative.