Jeff Bridges wrote in 040820 MMDigest, "... the metal ones [organ
pipes] are made out of (solid?) pewter."

Metal organ pipes can be made from many alloys but pewter is not among
them.  Most metal pipes are pure solder, a mix of tin and lead, called
pipe metal.  They use various mixture of that.  The more lead used, the
thicker the metal in the pipe and the duller or mellower the tone
produced.  The more tin, the thinner the metal and the brighter the
tone.

However, none of the pipe mixes are at the eutectic point of those
two metals.  (Eutectic point is when the mix is perfect for the mixture
to melt at the lowest possible temperature.)  That mix is reserved for
the solder that puts the pipes together.  You must use a solder that
has a lower melting point than the solder that is the pipe itself.
You are quite literally soldering solder together with solder.

There is also a special mix of metals that is called "Hoyt metal"
or "white metal".  I don't remember the mix, but it often looks like
pewter as it is usually polished to a high-polish reflective shine.
Looks like high-polish nickel.

Large pipes, longer than 4 feet, are usually made of zinc because pipe
metal gets so heavy at that size that the pipes would collapse upon
themselves from their own weight.

You can "read" the pipe metal itself as to how much tin there is to
lead by the size of the spots.  That's right, this tin/lead pipe metal
has spots.

When the pipe maker is giving a tour at Wicks, he lays a table of
pipe metal and he talks about it as the metal cools.  At a certain time
after laying the molten metal over the marble table, he reaches under
the table to flip the imaginary "spot" switch.  His audience is amazed
that when he reaches for the purported switch, the metal suddenly
blooms with spots all over it.  He knows exactly how long to wait to
make his audience think the spots are turned on.  It gets a good laugh
each time.

Brass can also be used for pipes but that is almost always used for
reed resonators like a brass trumpet, or a brass saxophone.  It is
mainly for looks, though since the same pipes with pipe metal
resonators sound the same for the most part.

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