For bikes with galvanized spokes and if you're doing a major rebuild, or wanting to preserve the original.

There's lots of time involved this way but dismantle the wheels and soak the spokes in white vinegar. Then just wipe them down with a rag. Next is to use a rag with Johnson car paste wax and wipe each one of them. Re-assemble the wheel.

It might be more trouble than its worth but........

good luck-