I must be improving a little - and have managed to locate a small but very useful precis of history kindly posted by 'robbo' back in September 05, the gist of which runs:
"Founded 1952 by Jonni, Martti(??) and Olavi Helander, brothers who had previously worked at Nuutajärvi as glassblowers. The works produced both 'art glass' and household wares. You occasionally see items signed 'Helander'. At this time some of the 'art glass' produced was Gunnel Nyman type controlled bubble items - I believe Helander brothers had made the originals when at Nuutajärvi.
Sold in a forced auction 1970 (there had been financial problems). New owner Rolf Alander.
1976 Humppila buys the Kumela glassworks from the Kumela family (Blomqvist had designed for Kumela). Kumela continued to produce glass by blowing and lead crystal, while the Humppila works concentrated on centrifugal casting and more mechanical means of production.
1986 Sold to Wärtsilä, owners of Nuutäjarvi. Subsequently, though the various takeovers/mergers, part of Iittala Oy Ab. Factory still exists, as part of Iittala".
I assume from this that my piece wud seem to fall somewhere between 1952 and 1970..............unless anyone has a better idea. thanks Paul S.