To make very hard dish inventor hollowed fireclay (7)

I believe the answer is:

petrify

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'to make very hard' is the definition.
(turn to rock)

'inventor hollowed fireclay' is the wordplay.
'inventor' becomes 'petri' (Julius Richard Petri, inventor of the Petri dish).
'hollowed' means to remove the middle letters.
'fireclay' with its centre removed is 'fy'.
'petri'+'fy'='PETRIFY'

'dish' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for petrify that I've seen before include "Scare stiff" , "Paralyse with fear" , "Turn to stone" , "Frighten stiff" .)

I've seen this clue in The Telegraph.

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