Seemed angered by, which was all too illuminating (6)
I believe the answer is:
glared
This clue could be a double definition.
'seemed' is the first definition.
The definition and answer can be both to do with perception as well as being past participle verbs.
Perhaps they are linked in a way I don't understand?
'angered by which was all too illuminating' is the second definition.
Although both the answer and definition are past participle verbs, I don't see how one could define the other.
Can you help me to learn more?
(Other definitions for glared that I've seen before include "Was too bright" , "Glowered" , "Lowered" , "Stared fiercely" , "Looked angrily" .)