Interesting discovery

Suggest you treat solid conductor cables very carefully (once set up....don't move them at all if you can avoid it).

Most cable problems come from slightly broken, damaged or oxidized contacts - leading to high or intermittent contact resistance on conductors and/or reducing the shielding performance on shielded coaxial interconnects.

Braided wire, although slightly more expensive to manufacture than solid wire, is good for flexible applications such as speaker wires. Braided can be soldered more reliably and is much less likely to be damaged from flexure.

Since oxidation from copper would be green, might the white powder simply be excessive flux from the soldering during manufacturing. Excessive flux should not do any harm, provided you have enough of a well soldered contact area with the spade.

Just replaced the battery in the car today..... a huge amount of white powder with hints of green was what I found all over the +ve terminal and inside the connectors and wires leading to the starter motor circuit...so Uppermidfi is right about copper corosion being initially white. Absolutely no corrosioin or any signs of powder over the negative (Grounded) terminal.

Of course a car battery is polarized....DC always +ve at plus terminal...so this increases the pace of corrosion on one terminal enormously.....which begs the question why should Tgrisham's speaker wire do the same when audio is AC....?

This suggests possibly some rectification going on some where or a DC offset in the amplifier?

=> Tgrisham, I suggest you check for a strong DC offset from your amp....this might explain the white powder build up. BTW, to get rid of the corrosion on your cables (if that is what it is), simply soak the affected parts in a cup of water with Baking Soda....it shoud all fizzle and wash away.