Dave Clark wrote:

> How long does it take to dry burnt shellac holding a valve seat into
> the block (similar to a Wurlitzer valve unit)?  I was thinking it
> should be about a week.
>
> I "re-glued" one using some burnt shellac that has been sitting
> around for a while (years).  I did this in mid-December.  I went to
> test the unit this week and the valve wouldn't stop leaking.  When
> I took it apart the valve had pushed the seat out of place because
> the burnt shellac was still quite soft.  Wouldn't hold a darn thing.

I have worked with burned shellac for years.  I have noticed that when
it is fully burned to the correct point it will last forever.  I had
some I found from a 1911 organ installation in a corked whiskey bottle
and it was still good.

However, normal shellac that is not burned will reach a time in its
life when it will not dry at all.  Sometimes you can paint it with
alcohol and make it dry but I usually just wipe it off with the
alcohol.  I can only surmise that your burnt shellac was not fully
burned.  I could see how it would not dry if the aged shellac was not
fully burned when you made it.  The burning process caramelizes the
sugars in the lac and that is why the burned version smells a bit like
a caramel apple.

I save old shellac and when it gets too old to dry, I find I can burn
it and it dries just fine thereafter.  It is possible that if you burn
your present "old" burnt shellac further until it reaches the right
chemical change, it will dry just fine as well.

When I apply burned shellac I apply it with one of my plastic glue
bottles I use for hide glue and let it sit 'til the next day.  It is
firmed up but not dry by then.  Full drying takes weeks.  After one
week it will usually not be oozing if you press on it.

D. L. Bullock    St. Louis
http://www.thepianoworld.com/