Being sloppy during a brake bleed I ended up with a squealing brake and several applications of disc-brake cleaner failed to improve the situation.

So I got out my Karcher SC5 steam cleaner and blasted the rotors and then the pads and, with one extra application of disc-brake cleaner, the squealing is now gone.

It wasn’t apparent when blasting the rotors than anything was coming off but the (aztec organic) pads certainly cleaned and lightened up.