thanks Leo, when I asked the manufacturers they said they just make and install, they don't treat. Now, we did have a look at cedar windows they had made and were treating in the workshop with a stained lacquer the client had provided. Saying that, the quotation did include priming and treating of the windows but I'm half afraid they may install them without anything on them. I don't mind prociding them with the oil or whatever or even going in and doing it myself before the glass is inserted, it's just knowing what to put on them. I haven't heard of tung oil before, is it similar to teak?.