Golden salve is an extract made from valley herbs, prepared by a thresher at a farmer's workshop using the "Process plants (to vial)" job and a glass vial. Currently, golden salve has no use, save as a trade good. One valley herb will yield five units of golden salve, worth 100☼ each, for a total of 500☼ per vial; processing valley herbs purchased from caravans (and thus coming in stacks of five) will fill each vial with 25 units of salve, worth a total of 2500☼.
Because golden salve is stored in vials, you will need to search for vials when moving goods to your trade depot, and then look inside the vial to confirm it has golden salve.
Even has that gold taste.