After reading the thread about storage ideas, I decided to check my accumulated stash. Most are in pretty good shape, all things considered. But one old sheet has turned really yellow. I know about using sunlight to 'bleach' the yellow out, never had much sucess with that method though.

Are there any other ideas or techniques that I could try?

I think there's no way to bring them back, but I think they would look king of weathered in a model. I think they would get more yellow if you put them in the sun, just look at old newspaper and they look tan.

Stick decals to pane on South window and leave this so on fortnights. This really works !!!

I tried the window pane method before, but the humidity ruined them after a couple of days. Might try sealing them in a clear plastic container and give it a go.

Using heavy weathering is a possibility. Maybe a dio of an attack near a sulphur mine?!? :-)

Thanks for your help guys.