Does anyone know what finish is used on BW bows ? Has to be one of the toughest, most durable, scratch resistant I have ever seen.

2 part marine epoxy, similar to Thunderbird Epoxy if not the same. Tough stuff but it does tend to yellow over time.

Marine epoxy is exactly right. Never had any of mine yellow. Never heard of it happening to anyone else either.  The oldest one I have is only 40 years old though. Maybe it takes longer than that:)