I cleaned the rotors that I intend to use, soaking them in carb cleaner
  for
a week.  They clean up real nice.  I noticed a patchy light almost looks
like an adhesive deposit on the side surface located between the side
  seals
and the edges of the rotor.  Does anyone know what this is? Thanks

Joe Berki

It is probably a Teflon coating that reduces the crevasses around the edge
  of the rotors
to reduce unburned HC storage for emissions reasons.

Paul Lamar

  Paul,

  I can feel the pitting with my fingernail.  It could be corrosives in the
  fuel or oil.  It is on the combusion side.  I will try to get pics.  Also
  found a small ding in the rotor face that is far away from the apex slot
  and
  bathtub.

  Joe Berki

Joe/Paul,

I've recently cleaned up two sets of 20b rotors and both had a light-colored material on the face of the rotor from apex to apex, but nothing on the sides.  Most of it was worn off, but you could tell that it had been coated with something.  My guess is that it is a ceramic thermal barrier.

Mark S.

Somebody should try chrome plating on the rotors. In theory that would reflect radiant heat from combustion, reduce the oil temperature  and improve the BSFC. Chrome plating works well on the steel rotor housing liner.

Paul Lamar
--
Paul
  wouldn't you worry about the chrome plating peeling of flaking off and causing damage?

Mike C.

It does not peel off the rotor housing. Electro plating is a very strong way of attaching one metal to another. That can not be said about ceramic coatings. I have seen what happens when ceramic coatings come off a rotor. It is not pretty. The rotor housing is turned to coarse sand paper.

It is easy to test. Take an acetylene torch and heat up an old junk yard bumper to 500 to 1000 F. I suspect you would need to get the chrome or steel to 2000 F melting temperature before the bond would fail. Unlike the rotor housing a piece of metal (the apex seal) is not continuously rubbed over the surface. Here is a severe test that Mazda performed on the chrome plating of the rotor housing steel liner.

http://www.rotaryeng.net/material-tech.pdf

Paul Lamar