This cheap PC keyboard will go first to test the effectiveness of my #retrobrighting process.
The very first step consists in a bath in dish soap and hot water. This should prevent grease and other dirt from blocking the UV light and the ozone.
While I was at it, I also threw in the PCB, just to see if my soap is safe for electronics.
Then I rinsed everything with fresh water and wiped with 70% isopropyl, which didn't seem to disturb the key engravings.