For what it's worth, I've used boiled linseed oil on several things - antiques, farm machinery, and wood projects (indoor and out) and haven't had any mildew issues. However, that's not to say it can't happen as RAH states. I have read about it being an issue with straight linseed oil. I believe the difference is that boiled doesn't mean "cooked" or "heated", it just means that dryers or thinning chemicals are added to it. Regular linseed oil takes months to dry in most applications where BLO dries and hardens much quicker. Up here in Iowa old timers have been treating their tractors, implements, and the underbodies of vehicles with it for decades to prevent rust.
