Which story was this, Cascade?
The dreaded VAT returns. Good luck x
Yes, mosaix, I thought your idea of a "slow mirror" was a very clever twist on the "slow glass" concept. The original slow glass concept was from the classic Bob Shaw story "Light of Other Days" (1966). I think his sequel to that story, "Burden of Proof" (1967), might have been the story you remember. Not sure about that. Later he wrote a novel about the concept, Other Days, Other Eyes.
Again, congratulations!
And thanks to Kerry for what you made a really fun challenge.