Frost polishing is actually referred to in a (IMO stupid) FAA document. The AAIB report on the Challenger 604 crash at Birmingham England a few years ago made specific (and, IIRC, scathing) reference to the FAA document in question...should be easy enough to track down....
Ah, here it is ....
AAIB Report
for example:
1.18.5.1 US Federal Aviation Administration Regulations
The following US Federal Aviation Regulations (FARs) dealing with icing of aircraft on the ground were relevant:
FAR Part 91.527: “No pilot may takeoff an airplane that has:···· (2) Snow or ice adhering to the wings or stabilizing or control surfaces; or (3) Any frost adhering to the wings or stabilizing or control surfaces, unless that frost has been polished to make it smooth.”
(my emphasis)
During the investigation, attempts were made to determine the definition of ‘Polished Frost’ and indeed how to polish frost. Nothing was found and the conclusion was that the explanation could have been lost in aviation history.
However, when considering why the crew of N90AG did not de-ice the aircraft, despite evidence that there was frost on the leading edge of the wing, the anomaly of ‘Polished Frost’ may be a factor. The existence of such a concept in both FAA and company documents gives an indication that some form of frost is acceptable and this may have influenced the attitude of this crew.
Enquiries were made of other national organisations to establish if the concept of ‘Polished Frost’ was widespread; neither UK nor Canadian Authorities recognise the concept. It is considered that the concept of ‘Polished Frost’ is particularly inappropriate and potentially dangerous to modern aircraft types and detracts from the importance of strictly observing the clean wing principle.
Accordingly, it has been recommended that the US Federal Aviation Administration, and all Authorities who follow FAA practice, delete all reference to ‘Polished Frost’ within their regulations and ensure that the term is expunged from Operations Manuals. (Safety Recommendation 2003-54).
Again, my emphasis.