[QUOTE=Fred Aspen;754432]The old rule, here in the US, and I think it is still the same, was:
The 'metals' refer to the metals used for each prong on a conventional 3 pronged plug.
It has been a long time but occasionally I would see plugs using a 'white' metal as well but I don't remember if this is substituted for the copper or the brass prong.
And now, of course, we have the larger prong to make sure the 'hot' line gets attached to the hot line.
In this enlarger the black wire is going to the outside of the lamp bulb socket. Since this is all run off of a two prong both sides the same size plug, one can't tell for sure I guess that Leitz used the black or white wire as the hot. Depends on which way you insert the plug into the wall outlet.
If this were just a lamp, it would be easy to fix. The focomat 11C has a on/off switch, a timer socket, and a small light box built into the base board. I'm a little afraid to start reversing wires to get the black going to the lamp socket center because I might end up making something else hot (like the outside of the lightbox).
I may just rewire it exactly as it is but run a ground wire from the metal column to an external ground.