The following was written by Emery Prior of General Die Casters, Inc.,
and is included in my book "The Mills Violano-Virtuoso," co-authored
by Mike Kitner and published in 1984 by the Vestal Press (currently out
of print):

  "The term "pot metal" is a catch-all to cover any metal or mixture
of metals that would melt in a pot.  Generally this includes zinc,
aluminum, lead, tin, bismuth and other metals or combinations with
a melting point of approximately 1200 degrees [650 C.] or less.
Technology at the turn of the century was simply the ability to melt
materials, get them to mix and stay in solution, pour them into a mold
and end up with a finished product that had no significant shrinkage,
was machinable or polishable, would hold together - at least for a
reasonable period of time - and looked presentable.  Every foundry had
their own unique mixture which was formulated, more than any other
factor, by the availability and cost of raw material or scrap.

  "Mills used just about any and every casting process and material
known, including brass, aluminum and iron, but it is probable that zinc
is the major component of all Violano castings in which cracking and
disintegration is involved.

  "Around 1900, zinc for die casting was available in 98% pure form and
was then alloyed with 6% tin and 3% copper to give it some strength and
make it somewhat castable.  It was discovered later that a bit of
aluminum (0.5%) would help.  Unfortunately, it was discovered later
that this combination produced a material that had very poor
dimensional stability and promoted what is called "intergranular
corrosion."  This is the term used to describe the growing, warping and
cracking of deteriorated pot metal castings.

  "In 1922 it was discovered that the aluminum was not the culprit in
intergranular corrosion so much as were lead, cadmium and tin, and that
if these impurities were eliminated, big improvements would be made.
Unfortunately, due to so many years of alloying tin with zinc, it was
difficult to limit in contamination, because for economic reasons it was
customary (and still is) to rely on the scrap market to supply ingot to
foundries.  Then, in 1926, it was discovered that a very small amount
of magnesium (0.1%) would help counteract other impurities such as
lead, tin, etc., and provide more stability and reduce intergranular
corrosion.  In 1929 the processing of raw ingot was improved to yield
99.99% pure zinc from which the alloyers could then add just those
ingredients they specifically wanted, thereby creating a bit of
sophistication to the process.

  "Another popular method to improve "meltability" in the early days of
ignorance was to add a bit of lead to the pot.  This was absolutely
_devastating_ to the problem of stability and intergranular corrosion.
Today's standards permit a maximum lead content of .005% - that's
.00005.  This is considered to be so important that most die casting
plants will not even allow a lead hammer to be brought into the
building.

  "What it amounts to is that in the early years, no one knew any
better, and if it would melt in a pot - great! Gradually over the
years, however, the intergranular corrosion problem came to the
surface, especially in the warmer and more humid climates, and it took
years of study and experience to work out the problems and arrive at
the best alloys.  Many components are produced today by the die casting
process, from typewriter frames (remember, this was written in the
"dark ages" in 1984 when we still had typewriters - AR) and automobile
carburetors to kitchen appliances.

  "The following chart (not reproduced here) shows the content of
various pot metal Violano castings, as analyzed by Alexander Panzer of
Ohio Spectrographic Service.  (The chart lists the content of lead,
tin, cadmium, copper, aluminum, magnesium, iron and zinc for two
different weight arms, a bow arm support bracket, and three different
rosin boxes, all parts which frequently suffer from intergranular
corrosion in Mills Violanos).

  "Several points can be made which are generally in line with the
above comments on the history of the development of pot metal.  All of
the parts analyzed were _far_ beyond today's acceptable limitations for
tin and lead contamination, and all, of course, exhibited severe cases
of intergranular corrosion, to the point of failure or disintegration.
Magnesium, which in later years was used to counter the effects of tin
and lead contamination, is essentially non-existent in all of the parts
which were analyzed.

  "It is interesting to note that the rosin box parts had an
incredibly high percentage of tin, up to 13.5% - vs. the .005% modern
day limits - and that all of the rosin box parts appear to share
basically the same chemistry.  These parts must coincidentally have been
from the same run of castings in the same foundry, as it is
unimaginable that anyone would purposely alloy that much tin into the
zinc, even fifty years ago.

  "Most of the parts are finished with a "hot tin dip" coating, whereas
that method was in later years abandoned in favor of nickel plating
due to the cost involved.  Tin was cheap then; now it's very expensive.
This no doubt contributed to high tin content, as scrap castings with
the tin coating would have been remelted for further use, thus
cumulatively inducing ever greater amounts of tin into the foundry pot.

(End of text from Violano book).

You don't need to worry about repairing many of the old Violano
castings at this time, as you can buy new ones from Terry Haughawout,
560 Garfield St., Bloomdale, Ohio, 44817.  He also has new piano plates
for Violanos.

My own shop offers replacement castings for the pot metal parts that
usually go bad in Wurlitzer roll changers, not including spool flanges.
At this time, we don't have any, but if I get orders for six sets, I'll
have another batch made.  Our machine shop also made up some simple
fixtures, which I still have, for machining certain critical dimensions
on the changer parts when we restored six Wurlitzer changers within a
relatively short period some years ago.

Art Reblitz
Colorado Springs, CO

 [ Thanks for the article, Art.  Now I know why the pot metal casting
 [ for the Ampico B spool motor frame didn't warp: it was probably made
 [ after 1929.  -- Robbie