Old photo paper

[MattKing]

F1 means that it is surface "F" - glossy - and it is contrast grade "1" - lower contrast.

 

[Saganich]

Thanks Matt, that's what my instinct told me since it doesn't make sense to use high contrast paper with electron microscopy, lol, but the published package insert was confusing.

 

[cliveh]

Test a sheet from top, middle and bottom of the box.