Undercutting...?

[mimosatexas]

So I have been using 135S mesh for the past few years with SP1400.  Great detail and prints like butter until recently. 

Some details:
135S is the only white mesh in our shop.
I am having no issues with undercutting on 150S which is yellow. (Also no issues with undercutting on an 81/71 yellow mesh, but that count is too low to hold the detail we typically put through a 135S)
Have tried a new gallon of SP1400 and PHU, same issue, only on the 135S.
Consistent across all our 135S screens.
We have printed identical prints (reprint the art frequently, same set of films, same mesh counts, same coating technique, etc) in the past without the undercutting issue.

We recently moved and I have a feeling there is something up with the electrical at our new space due to a few other issues, but also think maybe something happened with our exposure lamp.  Exposures are generally taking a bit longer, but the undercutting isn't happening AT ALL on yellow mesh (even under a loupe as far as I can tell).

I have tried everything I can think of, even doing different coating methods, and its like white mesh is just unusable for us all of a sudden.  Any ideas?

[Doug S]

I had the same issue and I'm using DTS.  I really had to fine tune the exposure to within a second or 2 with a 1200 watt metal halide.  The problem went away.  I'm coating 2/1 dull side using cryocoat and exposing 90 seconds.  That's the only white mesh I have in house also. 

[mimosatexas]

I've tried 1/0 from each side, 1/1, 2/0 from each side, 2/1, 2/2. I have underexposed to the point of the emulsion falling off, and it sti'll is undercut a bit based on what I can see from the initial soak or wetting. I'm using a 5k MH. I do think the unit itself is having separate issues, but the undercutting is only happening on the one mesh count and color.

[ABuffington]

 S Mesh can get too much EOM with the same coating used on T Mesh.  1:1 would be minimal coating with a sharp edge. White is always going to undercut a bit more than yellow mesh.  Also take a loupe or microscope and check out your image in the details you are losing.  Sometimes the pico liter dots don't focus or scatter.  Looks ok by eye, but won't wash out, could be burn through in transparent areas.  How old is the bulb?  A fresh bulb can shorten exposure times and help on undercutting.

Al

[Sbrem]

We also had an issue with our lamp when we moved a couple of months ago. We went from a 240v service to 208v. We changed the tap on the transformer in the lamp to match the 208v.

Steve

[mimosatexas]

Checked the voltage yesterday and it is the same for both spaces and the switch is set properly on the unit, though I still need to actually call Douthitt and have them walk me through everything internally.  I'm sure a new bulb and cleaning the reflector etc is past due and could only help.

[mimosatexas]

S Mesh can get too much EOM with the same coating used on T Mesh.  1:1 would be minimal coating with a sharp edge. White is always going to undercut a bit more than yellow mesh.  Also take a loupe or microscope and check out your image in the details you are losing.  Sometimes the pico liter dots don't focus or scatter.  Looks ok by eye, but won't wash out, could be burn through in transparent areas.  How old is the bulb?  A fresh bulb can shorten exposure times and help on undercutting.

Al

Thanks Al.  Definitely aware of the eom differences between the thin thread and standard thread meshes.  I used to coat 110T 2/2 or 2/3 and found 1/1 on the S is basically the same.  I know white undercuts more than yellow, but figured the faster exposure time would generally mitigate the issue.  Really the biggest oddity to me is that it just started happening and the difference between the yellow and white is so drastic suddenly when it wasnt an issue before our move.  Obviously the move is the likely culprit, but I would think it would effect all exposures to some degree, not just the white mesh.

I'll post whenever I solve it, whatever that ends up being...