I also saw the MBSI article referred to by Jim Quashnock, and started
investigating a while ago.  There are at least two websites which are
relevant, www.evapo-rust.com and www.biosolutionsllc.com.  I contacted
Biosolutions with a view to getting Evapo-rust in the UK, but so far it
is proving too expensive due to carriage costs.  Note that the article,
by Craig Smith, only relates to rusted _steel_ disks.

My investigation also revealed a UK product called Biox.  I have now
obtained some Biox and started trying it out.  It certainly works well
on rusted steel, as does the Evapo-rust cited in the MBSI article.  Biox
is claimed to be effective on other metals (but not to be used on two
dissimilar metals at the same time), whereas Evapo-rust is only good for
rust/steel.

I tried Biox on brass and it works well.  Following Kevin McElhone's
recent posting I have now tried Biox on zinc discs, and it works on them
too.  The exposed zinc is cleaned from a dirty dark grey to a light
bluey-grey in about 5 to 10 minutes.  I don't have any zinc discs with
heavy white zinc corrosion, so I can't confirm its ability to deal with
that.  The black lettering seems unaffected, as does the Polyphon gold
transfer.

In all of these tests there has been no evidence of strong chemical
reaction (Paul Camps mentions bubbles forming with Harpic, which is
typical of acidic action).  I am no chemist, but the various websites for
these other products seem to suggest that they lift off the oxides
without affecting the underlying metal; so there should be less effect on
the original material than with Harpic.

I will be meeting Kevin next week, and will pass on a sample of Biox fot
him to try.  If anyone else in the UK is interested, please e-mail me.
For those in the U.S., it might be worthwhile if someone sacrifices a
zinc disc to see if Evapo-rust does work on them too.

John Farmer,
UK
www.musicanic.com