looks it was coated in the past with something...that line in between pieces wasn't meant to be seen...try this...: tap on the top part with a solid thin object...how does it sound?...than weigh it...based on the weigh...and the diameter you could get the material it's made of..once you know the material you can find out what year it was made...(well not too precise but you can get a rough idea...)...it was clearly coated with something...no other traces of anything on the surface of it...?