Teak garden furniture is highly resistant to weathering and usually just needs cleaning with a garden furniture cleaner and a fresh treatment of Teak Oil to restore the appearance of tired looking wood.
Teak garden furniture that has turned grey or silver should be treated with a wood restorer such as Cuprinol Garden Furniture Restorer or Osmo Wood Reviver Power Gel prior to applying garden furniture oil. This will help to restore the original colour of the wood prior to oiling.