Some of the most popular specimens for amateur collectors are pyrite.  Often, these specimens deteriorate with time and become unattractive.  The natural reaction is to ask "What do I do to clean this up and make it pretty again?"  Unfortunately, curing the pyrite "disease" is not a matter of a simple polish job.

Pyrite "disease" is a misnomer, though, like Byne's "disease" in marine mollusk shells, there have been misguided attempts to link it with bacteria.  It is a humidity-driven oxidation of pyrite that affects the microcrystalline or framboidal forms far more that it does the large crystals.  The damage is preventable but irreversible once it has happened. DO NOT USE ANTIFREEZE!  Your informant got it all wrong.  It is possible to clean the reaction products off a the surface of a specimen using a "very" specific procedure developed by Lorraine Cornish and Adrian Doyle at The Natural History Museum, but this uses ethanolamine thioglycollate in a closed chamber.  It is not something you do casually with no training, as removing the specimen at the precise time is necessary to prevent its destruction.  The only way to slow the oxidation is to lower the relative humidity.  If the reaction has not started, keep it at 45% or lower; if it has, get it to 30% or lower. Desiccants will work -IF- you know how to use them.  It's not a matter of throwing silica gel into a case and walking away.  Anoxic enclosures also help a lot, but, again, this is not something to do casually.  DO NOT SEAL THE SURFACES WITH ANYTHING.  If you have an active reaction, coatings will not only not stop it, they may well make it worse by forcing larger areas to spall.  DO NOT REFER TO OUTDATED LITERATURE.  There is some amazing garbage out there about pyrite disease.  The best work on this is done by Frank Howie, Rob Waller at the Canadian Museum of Nature (who has done the best work on the specific mineralogy of the reaction) and Cornish and Doyle.

So my advice is:  1. If it ain't broke, don't fix it. If you don't have problems, don't do anything except keep an eye on things.  2. If you can't keep the RH below 45% and you think you may have problems, start with a preventive approach.  There are published descriptions of macro- and micro-climate control for collections in storage.  Museums have the directions for making anoxic enclosures and some advice on using and reconditioning desiccants.  For a large collection, you may wish to consider installing climate-control equipment for an entire case or cases; again, there are references for this.  3. If you know you have a problem, the first step is to remove the specimen from its storage environment to a work area.  Brush away and discard the dry powdery reaction product.  (That's a DRY, soft brush).  You may not wish to do anything more other than rehousing at this point.  The Cornish/Doyle method is not for the untrained, and often not for the trained.  There is no magic chemical or technique that will make the damage go away.  There is no disease to be cured.  Low RH is the answer.  4. If you have a collection of known reactive specimens, go ahead and make anoxic film enclosures anyway even if you've slowed the reaction (it never stops).  Reason: The reaction liberates sulfuric acid that can damage other specimens and storage materials.  And, encapsulate (NOT laminate) the specimen labels so that they are not in contact directly with the specimen.  (Yes, there are encapsulation directions, too.)  Less really is more.

I strongly recommend that you get a copy of "The Care and Conservation of Geological Material: Minerals, Rocks, Meteorites and Lunar Finds", edited by Frank Howie of The Natural History Museum (London) and published by Butterworths.  To find out more: Chris Collins of the Geological Conservation Unit, Sedgwick Museum, Cambridge University has started a newsletter for this subject.  For more information, you can contact him at the GCU, Madingley Rise, Madingley Road, Cambridge CB3 0EZ, UK, or at cjc1001@esc.cam.ac.uk.