Glassware in factory fire -- oil mostly involved (10)

'glassware' is the definition.
Both the answer and definition are singular nouns.
Perhaps you can see a link between them that I can't see?

'factory fire oil mostly involved' is the wordplay.
'factory' becomes 'mill' (synonyms).
'mostly' means to remove the last letter.
'involved' is an anagram indicator (involved can mean confusing or complex).
'fire'+'oil'='fireoil'
'fireoil' with its last letter taken off is 'fireoi'.
'fireoi' with letters rearranged gives 'efiori'.
'mill'+'efiori'='MILLEFIORI'

'in' is the link.

Can you help me to learn more?