"Max Mahanke" schreef
However, when faced
with the question, what causes purpleheart to revert from the vivid purple
to its purplish brown color over time he didn't know for sure. In
researching this on the web, one camp says exposure to UV over time and the
other camp says oxidation. The UV camp says use a finish with UV blockers
and the oxidation camp says use a water-borne finish.

***
As I don't know for sure either, and there is a never ending stream of new
finishes being introduced, again the question :
"What finish will let purpleheart keep its purple color?"
PvR