I am making an audio cable from a used mic cable. It looks like a
decent enough cable: braided shielding, paper and cotton threads, and 2
signal wires in good condition. The shielding though, looks green and
feels waxy.

My question is: is it corroded and useless, or has it been treated in
some way and can it be cleaned so that connectors (1/4" jacks) can be
soldered on? If so: what would the appropriate solvent be?
Thanks for your help.