Plain glazing or extremely crude china (9)
I believe the answer is:
porcelain
'china' is the definition.
(I've seen this before)
'plain glazing or extremely crude' is the wordplay.
I cannot really understand how this works, but
'or' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for porcelain that I've seen before include "Fine white ceramic" , "Form of ceramic" , "fragile goods" , "Fine earthenware" , "Crockery" .)