Mandruzzato also did some vases that have the two colors coming together, so both Mandruzzato and Oball are good possibilities. I didn't know Oball made any faceted things, but I wouldn't be surprised if they did. The sharp corners of the diamonds is characteristic of Mandruzzato. Some other companies have diamonds that are ground at the end, so the corners are squared off. I don't know what Oball's looked like, so can't help there.