Originally Posted by
750XL
Always the Captains call, though personally more often than not through experience I've seen the Captain ask the ground crews opinion and took their word for it rather than their own (generally, what else has been deiced, when, who, what aircraft, etc).
I'd be surprised if anything departed in -12c without deicing.
Captain's call always! As a Captain, if I see (or even think) there is ice, rime ice, frost or any contamination on the wing it gets de,-iced. No, the Captain doesn't "take their word for it". The de-icing or anti-icing mixture (usually both) is entered in the tech log; type, application temp, time, etc is carefully recorded. If the hold-over time is exceeded, then it gets re-applied.