While the biological merits of old dark comb are interesting, we no longer
live in the pristine un-contaminated woodlands of the colonial era.  Wax
acts as non-polar solvent and a good fraction of all pesticides readily
"find a home" in wax, and even high temperatures cannot eliminate these
substances.  There was that anecdotal story of a worker at a wax processing
facility that had to step outside for fresh air because of the
fluvalinate.  The mistakes of the past continue to haunt Beekeepers.

e.g.,
High Levels of Miticides and Agrochemicals in North American Apiaries:
Implications for Honey Bee Health
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0009754

*Almost all comb and foundation wax samples (98%) were contaminated with up
to 204 and 94 ppm, respectively, of fluvalinate and coumaphos, and lower
amounts of amitraz degradates and chlorothalonil, with an average of 6
pesticide detections per sample and a high of 39. There were fewer
pesticides found in adults and brood except for those linked with bee kills
by permethrin (20 ppm) and fipronil (3.1 ppm).*

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