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MAURE!!!

Posted on Thu, 10 Jun 2004 at 2:12



We do alot of one color (BLACK!) halftones. We pretty much have them down to a science... But, our one constant problem is maure. We've tried everything, dot angle, exposure time, newton rings, stretching, angling the films...Any body know something We don't? Please...

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Anonymous says: Sure. Take whatever screen mesh you have and divide it by 4. Then print out an elliptical dot at 22.5 degrees. Should get rid of your problem. If it doesn't, try dividing by 4.5. posted on: Thu, 06/10/2004 - 5:26pm
Anonymous says: What are you printing on? If you are printing on a textured surface, like a banner material, or a textile, you might get a moiré pattern due to the surface that you are printing on. The cure for this ...

What are you printing on? If you are printing on a textured surface, like a banner material, or a textile, you might get a moiré pattern due to the surface that you are printing on. The cure for this type of moiré is usually a bit costly. YOU have to print a under coat on the substrate to smooth out the surface that you want to print. If you are doing graphics printing, this could be a clear coat or a white (or what ever the stock colour is). With textile printing, printing the colour of the shirt or a white under base will usually work. Substrate moiré cannot be solved in the screen!! Even if you make the best screens in the world, you cant make a halftone print good on a gravel road!!
Another thing that you might have over looked could be you ink selection. Are you using a halftone ink to print your halftones? Halftone ink does not flow out after it is printed. It will stay put in the place that you want it to. Which means that there should be no surprises after printing. What you see in the screen mesh should be what you print. With conventional ink, the opposite can happen. The conventional ink is designed to flow out and cover as much as it can, which is a nightmare for halftones. We don’t want all of the dots to "be as one" with each other. This of course can lead to moiré patterns and optical jumps in the tonal range.

Well I hope this helps a bit.

Best regards, Peter Duff.

posted on: Thu, 06/10/2004 - 10:48pm
Anonymous says: Peter, I can see the moire (thanks for the spelling) in my screens. posted on: Mon, 06/14/2004 - 4:14pm
Anonymous says: Shawn, now that you know how to spell it, just curious as to whether you tried the angle I mentioned? posted on: Mon, 06/14/2004 - 11:33pm
Anonymous says: Ok.... now we know where the moiré is starting. Not the substrate... but the screen. There are a few different reasons for the moiré to pop up in the screen. Lets start with the first one that is usually ...

Ok.... now we know where the moiré is starting. Not the substrate... but the screen. There are a few different reasons for the moiré to pop up in the screen. Lets start with the first one that is usually a good place to start.

1. The film. Yes that’s right .the film. If you are using an Oyo or an aspect unit to make your films, the image setter its self will create a moiré like pattern in the film out put. Depending upon what angle you choose. Check the film before you shot to make sure that this is not the problem. If you are using an inkjet type of plotter to make your films (Quadra, Epson, mimic Jv-4, etc.) the films might look good before shooting on the screen, but you can get a moiré after exposing the screen. This is due to not having a "hard" dot on the positive. The centre of the dot will be very opaque, but the edges will not and the light will burn through the lower density areas of the dot. This will cause a different image to be made in the screen than what you though you were getting. And what do you know... Moiré will pop up usually in the lighter areas like the highlights. You also should be checking to see what the density of your film is as well. If your Dmax of your film (the dark areas) are not at a density of at least a 3.5, then the above mentioned problem will happen every where.
2. Make sure you have enough vacuum pressure during exposure. I know you said that you were checking for this already, but I just wanted to make sure that you were getting the Newton rings” before” you turn the lamp on. Over exposure can cause moiré. Under exposure usually doesn’t.
3. What line counts are you printing? Jerid ‘s little rule of thumb is close to what I use, but you have to remember one thing. The ratio of screen to line counts changes after the mesh is stretched. Ok … so say you were using a 55line screen. The ratio I use is five to one. So … 55 x 5 = 275 mesh that I would need to print a 55-line halftone, without moiré, with an 8 to 93 percent tonal range. So if I pick, say…a 280,40micron mesh that should be ok right? Wrong! The 280 mesh will have a weaving tolerance of +- 3 % and an elongation of about +-3 to 7 % depending upon who’s mesh you are using. So if you do the math… 280 x say 6%= 16 threads. 280 – 16 = 264final mesh count. A bit off of the magic 275 number that we thought we needed. To make matters worse, the higher we go in screen tension, the farter away we go from the specified mesh count that we though we were using. So… build your line counts to your stretched mesh counts, NOT your specified counts on the bolts of mesh that you ordered. Your 280 is now a 264, so divide 264 by five to give you the line count you should be using for that mesh. In and around the 52 to 53 line should work fine I would say.
4. OK the last thing that I am going to talk about tonight is screen stretching. We know now how to set up the line counts that we want… but there is still a nasty little problem out there that we have not talked about. Balanced stretching. One of the biggest problems that I have seen in the stretching of mesh is a not tension problem. The real problem is that the mesh manufactures have a very hard time weaving a bolt of mesh that has an exact mesh count weft and warp. Lets say that the un-stretched mesh has a tolerance of +-3% again with our 280 meshes. That means that our un- stretched mesh could be at 288 weft (the short way across the bolt) and 272 warp (the length of the bolt). What this means is that we now have two different mesh count to deal with when trying to get rid of the moiré. Even when the mesh is perfectly even in tension, the mesh counts weft and warp will not be symmetrical. This will almost always cause a moiré patter that looks like an oak tree, or large wavy lines. You want to count your threads before you stretch, while you stretch, and after you stretch, to see what kind of things are going on in your stretching process. Right down the numbers and look for any variation in your stretching methods. Try to assign tolerances of about 4 to 5 treads between the wefts &warp mesh counts when you stretch your screens. (E.g. 264 warp / 269 weft). And above all, try to be consistent.

Well that’s enough for me for one night .I hope this helps a bit more. Keep me posted if you need any more help.

Best regards, Peter Duff.

posted on: Tue, 06/15/2004 - 1:22am
Anonymous says: Not that I'm aware of. I did send that info to our art room. No reply yet. I will let you know. Thanks posted on: Tue, 06/15/2004 - 6:01pm
Anonymous says: Thanks for the input guys. But I think you hit the nail on the head with the stretching Peter. But unfortunatly, there's really nothing I can do about that right now. Thanks again, Shawn posted on: Tue, 06/15/2004 - 7:41pm
Anonymous says: You can get the screen mesh counter ,screen angle counter, and line screen testers from Mike Ruff at Reyhan Pgf. here is the link mike.ruff@reyhanpgf.com posted on: Tue, 06/15/2004 - 7:59pm
Anonymous says: Check out KIWO.com for the testing equipment and a ton of screen making articles. Good luck!!! (p.s Where are you located) Best regards Peter Duff. posted on: Tue, 06/15/2004 - 8:01pm
Anonymous says: Hey, Thanks again for all your help! I'll look at KIWO and talk to Mike Ruff. Minnesota. posted on: Tue, 06/15/2004 - 10:13pm

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