Grimrock

Turns out I did leave it behind in a pile of junk...
Boy don't I feel silly.

I've gotten down very far (Level 7) but haven't found the Mortar. A friend found it back on level 2 or 3 in a bag. He showed me a picture of where it was on the map, I went to that area, but I had already collected what was there. Is the Mortar a random chance to get? I don't think I would've left ...

Wow. It was that obvious. xD
Thanks.

I've been trying to get past these portals but just can't figure it out.
I managed to get past them once before, though I think I glitched it since I seemed to have passed through as the portal was moving.

How do I properly get passed these things?