In regard to heating piano rolls via a microwave...It brought to mind
a method I use to shrink piano rolls that have been produced on poor
quality paper, or have expended drastically and will not track properly
from damp or humid conditions.

We have an old rotary clothes ironer. The entire roll can be fed into
the ironer and it will roll through the roller and over the hot surface,
very nicely.

Since the take up spool in our Ampico is removable, I play the roll to
the end.  I Carefully remove roll spool, along with the take up spool,
taking the entire roll and two spools intact over to the ironer machine.

Insert the paper of the roll from the side of the ironer roller, lower
the roller, and as the roller pulls the paper over the hot shoe of the
ironer, use both hands to rotate the roll the roll back on its spool.
The entire process takes about as long as the playing time of a roll.
(Then you have a hot roll!)

I figure the roller travels at about "tempo 80"  Do be aware of how to
use the controls of the ironer before attempting this method.  One
needs to stop and raise the roller now and then, to prevent the paper
from drifting sideways now and then.  The heat setting works best when
set for "cotton"

I know this sounds weird, but it works, at least temporarily, to shrink
a roll back to its original dimensions and allow the perforations in
the paper line up with the tracker bar holes. I had hoped the rolls
would shrink permanently, however I discovered after a few weeks, the
rolls will again expand under very humid conditions. Because the heat
is so intense, I feel that it most likely would kill any mold or bacteria.

Bruce Clark