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Discussion Starter · #1 ·
What I'm trying to find out is what would be causing diagonal lines to have a "pixelated" or staircase look to them?

I have just started exposing screens. I did two test screens using graphics of a German eagle to determine the optimum exposure time. I got this eagle graphic to come out great within a certain time frame.

Then I exposed my first frame that I intended to use. It has small and large letters on it.

The larger the letters are the worst they came out. The have a pixelated look to them. Like on a very low resolution monitor.

I looked at some shirts with the same design I had made at a local shop years ago. On those shirts, there is a W that has a slight pixelated look. The other letters it is not noticeable.

On my screen and test print, the W is much worse, and the other letters have a slight pixelated look.

When I looked at the diagonal lines in the W, it literally looks like staircases, not a smooth line.

I'm using a very simple exposure unit. It is the Lawson Quest, which is basically just a 500 W work light on a stand.

My positives are on R-film with an Epson 1400. The positives I'm using look great. I'm using 110 mesh.

When I was during test exposures. I printed out film with five German eagles that had lots of fine detail. I did two test where I exposed each eagle a different length of time. At five minutes they would come out perfect. I did not expect this problem with a large font after getting the small detail of this eagle to come out.

What are some of the things that would be causing this? Overexposed? Underexposed? Emulsion to thin? Mesh count wrong? Exposure unit too sucky?

Thanks for your help.
 

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Discussion Starter · #3 ·
SBQ 500, from Lawson. It is pre-sensitized, fast exposing stuff. It's red. It's a Lawson Brand version of the red pre-sensitive SBQ Ulano (I don't remember the letters).

I just burned a second screen and it came out much better the second time. The staircase look I was talking about is still visible on the W, but not anywhere close to as much. The rest of the letters came out very sharp.

The only thing I did different on the second screen is I used my screen I got from taking the Lawson two day class. It's already been burned and reclaimed three times now (never actually printed on). In the class we used am abrasive powder to "rough up" the mesh.

The screen I used before was brand new and had never been subjected to anything abrasive, since I don't own any of the stuff.

I cut the exposure time by 15 seconds, but that is only a 5% decrease.

So the abrasive powder is the only difference between the too, but I could immediately see a big difference so I think there are probably some other reasons it came out better on the second screen.
 

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Discussion Starter · #4 ·
It is not on the film. You can see it on the screen. It prints exactly the way it looks on the screen.

Can you see the steps on the film?
Can you see the steps in the screen?
Or does it just show up when printing?

If you can see the steps on the film, the film might be outputting at at 72 DPI or you might be applying a halftone screen at some lower LPI.

If the steps show up when the film is burned, it is likely a result of the mesh creating the steps. backing down your exposure to near the point of failure can allow partial cell is wash out, which can help to overcome the steps in the mesh. For none yellow mesh screens, i prefer to overexpose and have harsher edges.

If the pattern only shows up while printing, you could be seeing a moire caused by the knit pattern of the shirt. T-shirts have a vertical pattern, like a picket fence, running top to bottom. The edge cells of the text in the mesh will interact with the ridges in the shirt. In most cases the letter will end on the top of the last ridge, rather than in a valley.

Every printer needs to own a good magnifying glass. I've been using the same paragon magnifier for the past 25 years. What separates the paragon from other magnifiers is that it fold to ride in a pocket. It also utilizes an adjustable fixed focus with a locking ring to keep it locked in focus after setting, even when riding in a pocket. The glass is also very high quality.



No. 5410 Paragon 10X Triple Lens Folding Magnifier - MNF80

If you don't buy this magnifier, buy some magnifier. With a good magnifier, the source of the stair steps should be obvious.

fred
 

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Discussion Starter · #5 ·
I get what your saying.

For me the problem is worse with the larger font. I have large letters in IMPACT, and small letters in a "celtic" font.

In the Celtic font every line is curved. In the Impact font it is mostly straight lines. The curvy lines of the smaller font came out better.

I have a 158 mesh screen sitting here. Next I'm going to make another one that will have the exact same large font at the top. I'll see how it turns out.

It sounds like the mesh of the screen. Going from a 110 mesh to a 156 would shrink the stair steps.

One thing to keep in mind is that screen printing is viewed from an arms distance. Steps caused by a 110 mesh will probably not ever been seen by people looking at a person wearing the shirt. You might be worrying over nothing.

Overly small or thin fonts can show the problem the worst.

fred
 
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