Last weekend I visited the Roger Hiorns installation, Seizure, which is just off Borough High Street in SE1. If you've not heard about it, Mr Hiorns sealed the windows and doors of a soon-to-be demolished flat, poured copper sulphate through the roof, left it there for two and a half weeks, and then drained the liquid out. What you're left with is brilliant blue crystals covering every surface of the flat.
The flat itself had been almost entirely stripped, save for a bathtub and some lightbulbs, none of which escaped the crystallisation process. The bulbs look particularly interesting as they still function, and in some areas the heat of the bulbs has burnt the adjacent crystals to a chalky white colour.
I recommend visiting this fun and atmospheric exhibition (I believe it's been extended to 30 Nov), and they lend you gloves and wellies so that you don't stab yourself on anything. Just make sure you don't spend ages taking photos of one of the lightbulbs, only to bash your head on it the second you move away.
Below are a few of my photos, along with a drawing I've messed around with.
Close-up of one of the walls
One of the cystallised lightbulbs
Walls and lightbulbs covered in copper sulphate crystals