Cryptic crossword No 3,439

902 - Closure - also available at https://ibendr.github.io/xwd/bendr/index.html along with over 500 more

UNDERSET has only one S, while "needs rust" has two.

Thanks BenDR. The theme was transparent which helped. I guessed 30a, a word I'm not familiar with from the crossers as the fodder was't quite correct. I thought I'd completed it but no confetti so had to check the grid which revealed 27a wasn't what I thought was correct . I had 'situ' which I think is a valid solution also?

Another neat history lesson! So much to like, among them the clever pairing of 24d and 26a, loved that! The delicious 5a and 12a, the lovely surfaces to 9a and 6d, as well as 17d and 23a, which I just loved. Many thanks!