I would not bother with trying to 'clean' them. The iridium and platinum coating is not 'meant' to be wire-brushed. As such,
Do not gap
Do not clean
Do not remove
The only “maintenance” is replacement. One time installation, one time removal.
Iridium and Platinum tipped spark plugs are designed to operate under normal vehicle operating conditions for up to 100,000 miles (160,000 kilometers) without periodic maintenance. The Iridium or Platinum is only a coating, and is easily damaged.
When no engine performance concerns are present, Iridium and Platinum tipped spark plugs should not be removed for periodic inspection and cleaning of threads, doing so may compromise the spark plug’s ability to withstand their corrosive environment. The threaded area, although not sealed, serves as a protective environment against most harmful elements. Removing and cleaning spark plugs will introduce metallic debris and brush scrapings into the thread area which may further the corrosion process.
Chromate coated spark plugs should not be wire brushed or handled in any way once they are put in service. Chromium topcoats form a protective oxide on spark plugs that is not effective if scratched. Both coated and uncoated spark plugs will have the best chance of surviving a corrosive environment if they are left in position. Attempts to maintain spark plugs by removing them and cleaning the threads can actually create the corrosive condition that the procedure was intended to prevent.
As was said, they can be had cheap now; I just received FOUR Denso Iridium plugs for my vehicle, via Amazon prime, for UNDER $20.