Another suggestion: are you sure the tine is cut to correct length? My piano had a range of incorrect-length (too short) tines that had been tuned to pitch with extreme tuning spring positions. When I rearranged them into the correct length/pitch arrangement, they really came to life, both brightness and sustain. Required inserting a new tine into the range and shifting others up, disassembling and reassembling the new tine-tonebar combinations. A lot of work, but made a big difference. I polished all the tines with Wenol and ground the ends to exact lengths while I was at it.