Alan Douglas wrote in 101201 MMDigest:

> ... a synthetic substitute which looks like thin Tyvek. ...
> Has anyone had any experience with this material?

Hello Alan.  I used to be a clock repairman, specializing in antique
as well as modern cuckoo clocks.  My personal belief is that nothing
should be used in clock restoration except materials identical to the
original.  Understand, that means in modern cuckoos the use of that
Tyvek-type material!

I used it for years.  It works well for cuckoo bellows, as it is
airtight, and it glues well with hot hide glue.  On the down side,
it is quite a bit stiffer than zephyr skin, necessitating the use
of slightly heavier weights to close the bellows.  Also, it requires
a hard crease on the folds (unlike zephyr), which leads to fairly
rapid deterioration.

None of my household cuckoos (mostly post-WW2) were working when
received, all having split bellows cloth, while a couple of the
antiques (covered with zephyr) still function on original leather.
A positive word for leather: my Aeolian Orchestrelle, built in 1899,
is still playing on its original leather, some of which is zephyr.

Cuckoo bellows work only a few times an hour, average, but a bird box
might be called upon to play repeatedly, especially when in the hands
of child operators.  While the material might work well for a time,
the additional force required to drive the mechanism as well as the
additional "operations-per-hour" might cause fairly rapid failing of
the bellows.

In short, I applaud and approve of Tyvek for some cuckoo bellows,
and would approve of its use in a new singing-bird mechanism,
I believe it will probably be too stiff and/or too thick for this use.

Bob Loesch
Northern California