Initially, bohemian Catalan artist blows top because of pen (4)
I believe the answer is:
biro
'pen' is the definition.
(Biro is a make of pen)
'initially bohemian catalan artist blows top' is the wordplay.
'initially' says to take the initial letters.
'catalan artist' becomes 'miro' (I've seen this before).
'blows top' means to remove the first letter (the first or top letter is shot or blown away).
The first letter of 'bohemian' is 'b'.
'miro' with its initial letter taken off is 'iro'.
'b'+'iro'='BIRO'
'because of' is the link.
(Other definitions for biro that I've seen before include "Writing implement" , "Lazlo -, ballpoint pen inventor" , "Pocket item" , "writer" , "Type of ballpoint pen" .)