There is good zephyr skin, and there is poor zephyr skin, and few
suppliers and rebuilders know the difference. I suggest testing any
that you get before you use it in anything, regardless who it is from.
Also, make it clear when you order it that you will return it if it is
defective or unusable.
Granted, mechanical figures do not usually utilize the material to
its full capacity workload, as you will encounter in puff pouches and
reproducer piano pouches (as in the Amphion block valve Ampico used),
but one first should check to see what they can glue it down with.
First of all, if you cannot glue it down tight with straight hot hide
glue (without additives for oily substances), don't use it, because it
isn't really tanned properly. It has been scraped, laminated, and
oiled. That kind of "tanning" can only be put down with synthetic glue
or shellac, which messes up the area to glue on when you have to replace
it all. Let the hot hide fully dry, then blow compressed air into it
at about 25-30 pounds per square inch pressure [about 1.8 atmospheres
pressure]. It ought to hold. That's also a good pressure to test
pneumatics on, too.
Next, if it is rather stiff and "crinkley", toss it out or return it
to the seller. Finally, if you can see layers in it, where it has been
rolled together with its own collagen while wet and the material welded
that way into a sheet, wider than the gut would be, then get rid of it
-- it will delaminate and disintegrate later, from my own experiences
of having to remove it from somebody else's rebuilds, and including
one of my own!
As I understand it -- and if someone knows differently I'd like to be
corrected -- the animal intestine to be made into zephyr skin must be
delaminated first. It's sort of like sausage casing. But it can be
stuck together and made into a sheet, like vellum. It's then not as
durable for use as a flexible membrane. Only if it is all of one
layer, in one sheet, is it suitable for pouches.
I have seen this stuff used in recent player re-rebuilds, and none of
it has lasted very long at all. I suspect it was not purchased from
Leather Supply House, however. They may be a very good source for good
zephyr skin leather, and since I trust the owner as a leather expert,
I would more likely trust the stuff he sells. I do not trust my own
expertise with it, as I am not sure I could recognize all the tell-tale
signs of bad tanning, but I think that these are part of the story.
I have in the past warned everybody away from zephyr skin. I am still
concerned about it and I would not use it until I knew that it would
last. It has to be very, very thin and even in appearance, and like
good quality parchment in color. You can't have cloudy areas and
clear-looking areas on the same skin. And since zephyr skin cannot
stretch, it must be very soft and pliable to act as a decent pouch.
Covering cuckoo clock "Coo-coo" pneumatics is not nearly as sensitive
an application, and heavier material can be used for that.
These are a few things that I can think of to help decide about zephyr
skin. I'd like to read what others would come up with as a criteria,
too, as I have only used it once or twice in my business, very early
on, in the late 1960's, and I had bad luck with delamination about
three years later. I had to replace all those pouches with leather
-- for free.