Ever heard of these? Panclimatic resistors

Got a couple of Welwyn Panclimatic 10k 5% resistors in a lucky dip off ebay. Black body about 16mm long, 4mm dia, non- magnetic and what looks like a brass core. A bit vintage methinks, maybe 60's/70's.
Compared to standard metal films or holco H8's as the series res. in a shunt attenuator they sound much better- removed a layer of fuzz I didn't know was there.

I cant find any info on the web; anyone come across these before?:confused: