Mesh coating. Type the first thing that comes to mind.

[mooseman]

I would think the thinned area indicates the process of the coater rolling out / back at the end of the stroke, OR the beginning of the stroke where the coater is rolled in and possibly started forward too soon before the emulsion fully runs to the edge of the coater.
mooseman

[Sbrem]

For most of the '80's we used Advance's Swiss Yellow, 60 mesh, because of all the 60 meshes, it had the thinnest thread, 123 microns (why I remember that when I'm not sure what I had for dinner last night, I don't know) and always coated with the thin edge; one develops the proper speed and pressure after a few, and no more than 2 screens without topping off the coater...

Steve

[ScreenFoo]

Also, with very coarse mesh it's better to coat 1:1 dry it, then face coat print side to lower RZ value.  It takes a high viscosity emulsion to coat this to proper EOM constistently.  Better to seal off the mesh with an even coat of 1:1, dry, then come back with multiple face coats.

I'm glad you can say that without a bunch of people telling you what a bad idea that is.   

I can't really tell much of anything from that pic without seeing the rest of it.  On a similar note, I did some testing a few months back to see if my new screen guy was wasting time or not with his coating technique which is quite frustrating to watch for me.  I coated about 50 screens one afternoon and all I did during this particular coating session was document the level of emulsion in the coater and then measured the screens once they were dried.  The screens that were coated with extremely low levels of emulsion in the coater were noticeably thinner out on the edges but there was only a difference once you got well below 1/4 full.  The thickness gauge couldn't tell which screens were coated with a 3/4 full coater or a 1/3 and everything in between.  The results I saw didn't gel with traditional knowledge on the subject and full disclosure I've always kept the coater between 1/2 and 3/4 at all times and was very obsessive with that. 

I'd be interested to see if anyone else had the time or want-to to do a similar experiment the next time they do a coating.  It would be good to see if the results were similar to mine or if they're different I'd have to go back and get our procedures in order.  Let me know if anyone would be willing to do something like that.

I appreciate this.  My SOP for many years has been adding emulsion when I get under half or so.
I've never had a thickness gauge but have done print testing and couldn't find major differences in the results of anything but higher tolerance halftone work.  I stay obsessive with those screens.