Crossword Genius

Layer of molluscs damaged porthole frame (6-2-5)

Ross

I believe the answer is:

mother-of-pearl

'layer of molluscs' is the definition.
(layer in the shell of some molluscs)

'damaged porthole frame' is the wordplay.
'damaged' indicates an anagram.
'porthole'+'frame'='portholeframe'
'portholeframe' is an anagram of 'MOTHER-OF-PEARL'.

(Other definitions for mother-of-pearl that I've seen before include "Internal layer of shell" , "Decorative substance got from certain molluscs" , "Nacre" , "Iridescent material used in ornamentation" , "girl's mum" .)

I've seen this clue in The Independent.
Want a hint initially instead of a full solution? Install my app