Thanks for that David, that does sound like it. Would it be oxygen as well as light that turns it, and does it go yellow?

Mojo that sounds great. I have an oatmeal cam, and soon there will be a Smash cam and a Twinings chocolate indulgence cam. It's a tough job but I guess I'll manage.

My pinholes are here if anyone fancies a look.http://www.flickr.com/photos/f777/

Thanks Catherine