Hello Katamuki Im sure there are early bottles or pottery items to be found in your area. With a little research on the older island harbours you should be able to find a site that produces some earlier items. A few years ago I seen some turn of the century era Codd Stopper sodas from Japan that were really nice along with some early embossed crown top sodas.
Is metal detecting on the beach popular there in Okinawa?
Okinawa has very very few beaches! Almost all of the surf areas are hard rock which is very very sharp. The beaches that do exist where people swim are mostly man made or enhanced.
There are several areas where I have seen bottles among boat/ship debris, is there a quick way to tell if a bottle is old and not just new trash?