Possible Clues:

• Obscure relative a rector
• Sort of bomb with uranium going up in clouds?
• Not distinct in nuclear way
• ... rather dim, in Uncle Arthur's view
• Not fair: that's ambiguous
• Pawnbroker once had a right to be less than explicit
• It's not obvious that this is a relatively backward artist
• Nebulous nuclear fall-out
• Nuclear explosion not easily explained
• Not transparent or free from doubt