Sorry to resurrect an old post, but I did some more lith printing last night after a hiatus due to darkroom frustrations.
There were a few posters who mentioned agitation or turbulence being the culprit, and my hats off to you! Lith printing seems to be particularly sensitive to this phenomenon.
Below are two prints developed one after the other. The left one was agitated only by flipping the paper every so often. The right one was left face up and the tray was rocked both front to back and side to side.
The differences in the edges are obvious, but the interesting part is that in a straight print, the people in the swings cutting across the frame are uniformly lit. In the print agitated by rocking, though the overall effect is darker, the people towards the center of the frame are noticeably lighter.
In the one agitated by turning the paper over, the overall effect is lighter, but the people are more uniformly dark all the way across the paper. It is certainly a more even print.
Tech details.. Fomabrom 111 grade 3 (not Variant III. That's the multigrade stuff.) Fotospeed LD-20 diluted 1+1+18. Developing times were right around 15 minutes with 3 stops over a straight print.
Sorry for the terrible picture! Digital taken with my cell phone.. yuck.