Lith failure two sheets in tray

I processed two sheets of Fomatone MG131 developer in Moersch Easy lith yesterday in the same tray. Same exposure. i wanted a few identical test prints to play around with toning.
the one that was on the bottom came out a lot darker. I had the bottom paper emulsion facing down and the top one facing up.
plenty of developer in my Paterson trays.

You really have to watch them come up. To do that you would need to have them side by side. Even then it will be hard to get them both in and out at exactly the same time. Maybe a use for those 'multi easels' littering e-bay that no one wants--put multiple images on the same paper so they all get processed the exact same way.

It's not a paper or developer fail, but user fail. When processing two sheets of paper at the same time, you have to consistently rotate them so that they spend the same amount of time at the top and bottom of the developer tray - the movement of the developer is different at the surface than it is at the bottom of the tray. I always wear nitrile gloves when doing lith and will agitate for 10-15 sec, then flip, then agitate again, then flip. Some people do a constant flipping throughout the entire development process, even with a single print (didn't realise this was a thing, until I saw several people do it a lith printing workshop with Tim Rudman). Even when you do this however, there will still be a slight variation in the prints, as hand agitation and flipping is never perfectly even, but they should be close enough for testing/toning purposes.

Edit: If you really want them to be identical, either have a tray that is big enough to hold both prints side by side facing up, or, use 2 trays side by side for the same purpose.

good idea with the flipping. I can try that next time.
I had a test strip stuck to another normal print the other day. I didn't bother removing it in the developer tray and then noticed that that part covered by the test strip was darker in the final print.
The test strip must have rubbed on the print below it and developed to a darker tone at that spot.