Half of them sketch vaguely from beginning to end (10)
I believe the answer is:
throughout
'beginning to end' is the definition.
I can't tell whether this definition defines the answer.
'half of them sketch vaguely' is the wordplay.
'half of' suggests halving the letters.
'sketch vaguely' becomes 'roughout' (I can't justify this - if you can you should give a lot more credence to this answer).
'them' halved is 'th'.
'th'+'roughout'='THROUGHOUT'
'from' is the link.
Can you help me to learn more?
(Other definitions for throughout that I've seen before include "during the entire proceedings" , "all the time" , "Completely" , "Everywhere" , "from start to finish" .)