Smearing tar (gilsonite/asphaltum) on your quarter-sawn piano case gives
a great appearance.  I noted that neither gilsonite nor asphaltum popped
up in the MMD archives search, so I figured I'd contribute a few more
terms.  Allow me to explain.

As a weekend pneumatic enthusiast, my re-building projects take a lot of
time, and I have plenty of time during the week to ponder different ways
to do my work--they are not always better or faster, but I always learn
something.  I have not been very impressed with off-the shelf wood
stains available these days, and got around to experimenting with
alternate wood colorants--particularly those that would have been in
frequent use in the early 1900's.

One such colorant was brought to my attention in Michael Dresdner's book
"The Woodfinishing Book".  He states:  "Although asphaltum is not easy
to find in art-supply stores, it is too good a material to pass up.  The
base of this tar-like gunk can be either petroleum or bitumen (coal),
but the colorant responsible for its beauty is a natural mineral called
gilsonite.  Use it as a stain on raw wood and you have a deep
brown/black color perfect for dark Jacobean or mission oak...."

I searched around art stores here, figuring that anything petroleum
based would be amply available in an oil town such as Houston.  Nobody
heard of it.

Finally, I contacted Ziegler Chemical and Mineral Corporation, a
processor of Gilsonite/Asphaltum and had the chance to discuss this with
a very knowledgeable sales person.  Check out their web-site -- it gives
a lot of product characteristic information:

     http://www.pioneerasphalt.com/gilsonit.htm

Their main customers buy huge quantities of the material, and a weekend
enthusiast won't even come onto their customer-base radar screen.  But
you can get it in relatively small quantities from their distributors.
Gilsonite is used for drilling mud, newsprint inks (it even smells just
like a brand new newspaper), and is essentially a roofing tar.  The
Ziegler products are based on a coal-like substance (rather than oil)
found only in Utah and apparently has better properties than the
petroleum-based cousin.

Properties of this material make it suitable only for oil-based topcoat
finishes such as an alkyd resin varnish.  Shellac or water-based
finishes will not adhere well according to their product information.
It is fairly colorfast (won't fade).  Have you ever seen faded coal?

I was advised to obtain a pre-made "cut" of gilsonite.  A cut is the
ratio of gilsonite to solvent--just like a shellac cut.  The recommended
product was number AA4047--this had the consistency of loose roofing
tar--or a very thick custard.  It is interesting that gilsonite behaves
more like a dye stain, as it goes into solution (not suspension) when
it's cutback.

Application of gilsonite is a rubber-glove activity.  Just dip any old
rag into the stuff, and smear it on.  I thinned my batch a little more
with mineral spirits to make it more of a gel.  It does have some
grain-filling capability, so a grain filler is not really needed, except
for particularly open grain.  You could easily mix the gilsonite as a
colorant to a grain filling paste--just make sure the paste is
oil-based.  I smeared across grain, and let it dry to a haze (10-15
minutes) and then used a clean cloth or 000 steel wool dampened in
mineral spirits to just remove excess.  On quarter-sawn oak,
conventional pigment stains can sometimes leave a too-pronounced fleck
(stripe), in my opinion.  As gilsonite behaves as a dye, the fleck is
muted, but clearly visible.  Since the resin varnish tends to soften the
stain, I applied a thin coat of varnish as a seal coat with very little
brushing in.

For those particularly adventurous, you can make your own cutback, but
the salesman advised against it.  To do this, you start with a bag of
rocks (crushed gilsonite) straight out of the Utah ground, such as their
product ZECO 11.  Shoot for a cutback of 37% gilsonite by weight, with
mineral oil as the solvent.  If you add 10% toluene or xylene, it will
accelerate the cutback process.  Dump everything in a closed, but
vented, container--well away from any structure and in a ventilated,
covered, area.  Stir every couple days.  In about a week the "raw"
gilsonite will be in solution.  If you are in a rush, you could heat it
mixture.  Zieglar use something like a pressure vessel with steam coils
to do the cutback.  Force the mixture through a filter to remove larger
particles that are not gilsonite (small pebbles, sand, etc.).

I managed to secure a gallon of AA4047 from their Houston distributor:

    Crozier Nelson Sales
    15710 JFK Blvd, Suite 180
    Houston, TX  77032
    281-219-1611

They have distributors scattered across the US (and world for that
matter).

A further note:  roofing tar found in the home improvement stores often
has fibers, particles, and may be synthetic.   Avoid using these
materials on your piano.

I was a little apprehensive about smearing gilsonite on my current
project, but I the results turned out very nice.  The biggest drawback,
by far, is the time needed to apply enough coats of slow-drying varnish
topcoat.