We often talk of sealing the wood in our pneumatic devices.  To
give visual evidence of that need, I am sending a picture taken
inside an Estey organ chest.  When I first acquired this organ over
20 years ago, I didn't do much restoration, but I did give the
blower a thorough cleaning.  At that time I assumed that the blower
had "inhaled" coal dust or coal soot over a period of many years.

Now, that coal dust residue can be clearly seen inside the chest --
black accumulations of carbon gather at the pores in the wood.
Obviously, air was passing through those tiny channels.

Vacuum operated instruments don't leave such obvious clues as this,
but this should serve as proof that shellac should be used to seal
most pneumatic devices.

Bob Taylor
Missouri

 [ Coal dust in porous wood
 [ http://www.mmdigest.com/Attachments/15/03/28/150328_173135_coal%20dust%20sucked%20into%20unsealed%20wood.jpg