Howard Sanford asks how to mute or muffle trombones on a 101-key
Mortier [161025 MMDigest].  These are inherently loud so the
easiest way is to mute them by locating the outlet from the
register box and pull out the trombone tube.  The outlet can then
be blocked by a small cork to prevent unwanted wastage of wind.

Reed pipes can be reduced in volume by narrowing the neck of the
resonators.  Unfortunately they can only be accessed by removing
the pipes from the organ -- a major undertaking on a large Mortier.
If you pull the resonators from the boots (at the narrow end where
the resonator is machined round, with a brass collar round it) the
hole can be blocked with wood dowel and drilled with a hole somewhat
smaller than the original hole.  The amount of reduction will have
to be tested by trial and error.

Under no circumstances mess with the open end of the resonators as
that will undoubtedly spoil their tone and tuning.  Likewise, don't
meddle with the reeds.  You'll never get them playing again unless
you are a reed expert.

Of course, you can always put up with the sound as it is, just as
Mortier would have liked.

John Page, UK