When restoring my Winter & Co. Player for conversion to "O" roll
orchestrion I found the ivories were yellowed.  The black keys around
the centre of the key board had 50% of the paint off.  I believe it
was played more by hand than by a roll.

However, to whiten the ivories, not knowing any better at the time,
I used 1500 grit and/or 600 grit emery paper, then used Brasso metal
polish to get the 'gloss' back.  This seemed to work okay.  I only
did five keys per day, as it was tiresome.

My parent's piano in the UK, purchased second-hand, I believe, in the
mid-1940s, was a 'Challen' make.  I believe it was a 'top' make.  The
ivories were good and white and with a nice 'grain' like I have never
seen before and since.  I remember that the keytop was a complete strip,
i.e., no split at the line of the black key.  Maybe the UK readers can
verify this.

Stephen Bentley
Vancouver, British Columbia, Canada