Are they always wire-wound ?
Repairing a scope found an O/C 12K vitreous resistor used as a ps dropper.
Still dark green body and clear writing, no board discolouration
and no reason to fail due to other failed components in line.
I've never cracked open one of these so did so . White
ceramic body and presumably a glass coating but no sign of any
wire. So I cracked open a new 1.8K vitreous and that used about
3 thou wire spaced about 120 turns to the inch between the white
and green. Returning to the ex 12K could not cleave the white
and green sections and viewing edge on with a x30 microscope
still could see no trace of any wire. Could it have been a metal-oxide
layer instead ? Even the 1.8K one would seem to be physically
very frail to use that small a guage of wire.

Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse