On Tue, 17 Apr 2018 14:48:31 +0100
T i m wrote:

To be of any use it needs to be part of the material and share
its thermal qualities.

I agree, that would be the best solution but conscious it may be
overkill in this situation (even as part of just experimenting etc).

Perhaps it's time to have a go at home anodising? Because that would
probably put the "black" in very good thermal contact with the alloy
surface.