Hi Richard.
Sorry. Only just noticed this posting here. Unfortunately, my finish isn't exactly piano black. It's black alright but definitely not piano quality.
I finished the plywood with two coats of white Dulux wood primer, sanded down lightly in between coats and finished with two coats of Dulux Satin black oil based paint. All paint was applied with a mini foam rubber roller kit from Homebase. I hate glossing anything so always use a roller. It gives a good even finish with no brushmarks. I think if I wanted piano finish I would probably go for a spray paint system. HTH.
Cheers,