Vinegar and lemon juice, that's what I was trying to remember! Good to hear that it does work well, I'm thinking of saving my old cleaning spray bottles and filling them up with some homemade stuff.

My main problem is that I use a lot of academic books, a lot of which haven't been digitalised yet. Maybe there'll be a big swing in the academic community to move towards digital publication! (Though I'm sure it won't bring the cost down....)