Locked up in Alcatraz in California for galvanising steel (4)
I believe the answer is:
zinc
'locked up in alcatraz' is the definition.
The definition suggests a singular noun which matches the answer.
'in california for galvanising steel' is the wordplay.
'california' becomes 'c'.
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'galvanising steel' becomes 'z' (I can't justify this - if you can you should give a lot more credence to this answer).
'in'+'c'='inc'
'inc' after 'z' is 'ZINC'.
Can you help me to learn more?
(Other definitions for zinc that I've seen before include "Metal used in galvanising iron" , "Blue-white metallic element, atomic number 30" , "Bluish-white metal" , "Type of metal" , "Sivery-white metal" .)