The deep, bright, intense copper reds are very stable. I have some
pieces which were done about 12 years ago and there’s been no color
shift whatsoever. Wax or lacquer isn’t needed to improve the stability
of the color, but either product will intensify it a little.
The duller salmon-brown, orange, or lighter (ands duller) reds seem
to “brown”, fade, or darken over time, but they will still retain some
of their redness. Wax or lacquer will intensify the color a little,
but do not seem to help much with color retention over a long period.