I must set the record straight, while Ken Vinen's thickened shellac
will work very well for many things, it is not burned shellac, and
we should not call it such.

When the shellac is burned, it changes chemically.  It becomes more
tenacious and it _really_ sticks to metal and other things.  The
drawback is it takes longer to dry to touch than thickened shellac or
PVC glue.  However, it continues to harden over time until it is quite
hard and solid.  Anytime you want to remove it just get out your Master
heat gun (500F to 750F degrees) and it softens within 6-10 seconds
enough to pull it loose from what it is on or trowel it off with
a pallet knife.

I use thickened shellac for many things.  I coat the inside of pouch
wells with it and the inside of pneumatic boards, feeder boards,
reservoirs, valve chambers, etc.  I use it because it dries much faster
than the burned variety and I need to get pouches and things going
without a couple of days waiting for the burned shellac to dry.  When
sealing Ampico valve blocks, however, nothing approaches burned shellac
for hold.  I adjust the valve seats and apply the burned shellac using
one of my plastic hot glue bottles I have made for me.  They can sit
several days for drying before I need to put them onto the stack in
most cases.

These are the methods for making thickened and burned shellacs: Ken's
method of using flake shellac works well but I use the lower quality
or left over liquid shellac.  (I save the flakes for the good finishing
shellac or French polishing jobs.)  Leave the lid off or pour out
a smaller amount and leave the lid off that for a few days.  Stir it
daily to puncture the skin that may form.  Check it regularly to
monitor how thick you want it.

Have you ever had shellac get old and you find to your horror that it
will not harden but stays sticky?  No problem, make the rest of the can
into burned shellac.  Take the liquid shellac and put it into a metal
can 3-4" deep at a time.  I use a coffee can.  Next, light a match to
it.  Have something flat and metal handy that will air seal the top of
the can for putting out the flame.  Do this in a semi dark room so you
can see the fire.  It is sometimes hard to see in the full light.

Swirl the can around and around.  I use both hands touching the can
around the bottom inch or so.  As long as your hand is below the fill
line of the shellac inside it won't burn you.  Alternate swirling and
letting it sit and burn.  Do not get too strenuous in the swirling or
you will slosh burning alcohol on you or the table or floor.  How do
you think I know this?

Depending upon how much shellac you start with, it will take 10-15
minutes or more to burn down.  It might burn down to half its previous
volume.  That varies.  It is difficult to tell how long it needs to go
until you have done a few batches.

You will notice as it gets close to being done, it begins to take on
a caramel smell that is distinctive from the alcohol smell of regular
shellac.  It darkens without being black.  Remember that it will
thicken further as it cools to room temperature so you want it thinner
than it will ultimately be.

When it is ready the burning really slows down when you are not
swirling.  Put it out with the metal panel over the opening.  I let
it cool a while before I pour it into the plastic bottles.  I make up
two or three batches at a time because when you do a few hundred valve
blocks or Simplex valve seats, it takes lots of it.  I will put out the
flame several times to check for thickness, then light it again and let
it go longer.

When I dismantled a pipe organ that began life as a tubular pneumatic
action, I found a corked 1910 whiskey bottle with dark brown stuff in
it that smelled a little like a candied apple.  The liquid was thick
but would pour out.  I discovered that was the burned shellac they used
to install the organ in 1910.  I took it home and found that it was
still good and worked as well as fresh burned.  Unburned liquid shellac
only lasts a couple of years before it will no longer dry completely.

I am sure someone here can tell us what happens chemically when the
shellac caramelizes to become a completely different substance from
shellac.

D.L. Bullock    St. Louis
www.thepianoworld.com