More Exposure testing and Dot Testing

[drdot]

Really nice photos and worth commenting on. The stencil edges are important to look at and not only the dot structure. What you're looking for is a lip of emulsion above the mesh. This is EOM (emulsion over mesh.) The reason this is so important is that it forms a containment area for the ink. As dots get smaller and smaller, it isn't possible to maintain 3 threads or mesh openings in the open dot area. All you really need is one mesh opening. Think of this an an injection port where you are injecting ink into the open cavity formed by the EOM.  It is entirely possible to reform the full dot shape if you have enough EOM.

This is one of the main ways to minimize moiré and dot loss in the very fine highlight dots that are effected by thread eclipsing.

[jsheridan]

Thanks for jumping in Mark. 
One more reason I want the USB scope with it's 400x power and angular view, you can see the stencil wall.

Got some more pics.. Silver based imagesetter film and stencil edge..  50 DPI @ 22.5 angle.
You can't get much better than this. Shot on a 270/34 @ 30n with Diazo based CP-TEX private label coated 2x2 with 140 LTU's on a MSP3140

[Dottonedan]

I have this image that I've created for a while now. It fits this scenario so, this gives a little idea of what Mark is talking about. As John mentioned, once he's using a nice clean dot from a real imagesetter, the WALL edges and dot cel are even easier to form.

I've heard the argument that using a thick stencil (or what would really be the optimum stencil thickness) is "too thick" by some peoples standard and the justification is that it would be similar to putting too much ink down through a long TUBE (the dot cel). If the ink is not thin enough, it will be likely to clog in that tube and not clear the screen. But, you really are not talking about having that thick of a dot cel like a qtr inch thick when using adequate EOM.

Your emulsion supply company will be able to tell you what is the accurate EOM for each mesh. From my understanding, EOM is different for the various meshes. A 300 mesh will have a different EOM from a 156 or a 110.  This means, to achieve those, you will need more costs of emulsion on lower mesh and maybe less on higher mesh.

Adequate EOM forms better image detail/clarity. If your ink is too thick, of course you may have difficulty, but that goes with almost any layer if emulsion thickness. Adjust the inks to suit the needs.


I see John has posted some new images. Those look great.  I've not loved even the best digital film printers but they do the job and some do a really great job but as John knows and has posed, you don't get much better than an imagesetter.  Even the Direct to screen as sprays and while capable of putting out minute detail, I think they are still not as good as a true imagesetter. No spray can cluster the dots so tight to equal the sharpness of a 2400dpi photo dot with 100% accuracy.

Johns 2nd image (the photo of the dots with emulsion and screen) looks to be spot on for image clarity and you can see a bit of the edge indicating a thicker cel. This looks to be a heavier coating than your first image of the ragged edged digital film.  What was your coating technique for your first set?  referring to (the first photo of the dots with emulsion and screen and the ragged edged digital films).

In my example below, this is to illustrate the extended level of emulsion needed. The top SMOOTH SURFACE represents the surface area "look" we are trying to achieve to form a good gasket or seal between the garment and the emulsion. The more the knukles protrude, indicates an inadequate layer of emulsion. Sure, most times it will still work, but not to it's full potential. If you are trying to achieve top quality prints or even award winning prints and provide consistant high quality work recognized by those with a keen eye for image quality, this is what you are looking for. In addition to the heightened image quality, you will also be able to maintain that image quality during hard vigorous production runs. It's harder to breakdown and holds up longer.

The darker inner section indicates the thickness of the threads and many people only reach a point of covering those threads with a very thing layer of emulsion. Some think the thinner the better on higher mesh.

This is a great topic, thanks for posting John.

[jsheridan]

I have this image that I've created for a while now. It fits this scenario so, this gives a little idea of what Mark is talking about. As John mentioned, once he's using a nice clean dot from a real imagesetter, the WALL edges and dot cel are even easier to form.

I've heard the argument that using a thick stencil (or what would really be the optimum stencil thickness) is "too thick" by some peoples standard and the justification is that it would be similar to putting too much ink down through a long TUBE (the dot cel). If the ink is not thin enough, it will be likely to clog in that tube and not clear the screen. But, you really are not talking about having that thick of a dot cel like a qtr inch thick when using adequate EOM.

Your emulsion supply company will be able to tell you what is the accurate EOM for each mesh. From my understanding, EOM is different for the various meshes. A 300 mesh will have a different EOM from a 156 or a 110.  This means, to achieve those, you will need more costs of emulsion on lower mesh and maybe less on higher mesh.

Adequate EOM forms better image detail/clarity. If your ink is too thick, of course you may have difficulty, but that goes with almost any layer if emulsion thickness. Adjust the inks to suit the needs.

This is why I always say the best white is.. the one you make in house that fits your screens and your coating techniques. The white that works awesome on a 120/32 with a 2x2 coat isn't going to work the same on a 150/48 with a 2x3 coating filled with 1/2 tones. You need to thin the thicker stencil ink down to clear the injection ports. Great term and way to think about the mesh opening. I've noticed the 3 thread was getting harder if not impossible to find a good dot in the high counts, now that I think back I saw plenty of single dots in the 5% range in the high mesh counts. Anticipating that and finding then using the right DPI for that count allows you to get those fine 3-5% tones.

I see John has posted some new images. Those look great.  I've not loved even the best digital film printers but they do the job and some do a really great job but as John knows and has posed, you don't get much better than an imagesetter.  Even the Direct to screen as sprays and while capable of putting out minute detail, I think they are still not as good as a true imagesetter. No spray can cluster the dots so tight to equal the sharpness of a 2400dpi photo dot with 100% accuracy.

Johns 2nd image (the photo of the dots with emulsion and screen) looks to be spot on for image clarity and you can see a bit of the edge indicating a thicker cel. This looks to be a heavier coating than your first image of the ragged edged digital film.  What was your coating technique for your first set?  referring to (the first photo of the dots with emulsion and screen and the ragged edged digital films).

In my example below, this is to illustrate the extended level of emulsion needed. The top SMOOTH SURFACE represents the surface area "look" we are trying to achieve to form a good gasket or seal between the garment and the emulsion. The more the knukles protrude, indicates an inadequate layer of emulsion. Sure, most times it will still work, but not to it's full potential. If you are trying to achieve top quality prints or even award winning prints and provide consistant high quality work recognized by those with a keen eye for image quality, this is what you are looking for. In addition to the heightened image quality, you will also be able to maintain that image quality during hard vigorous production runs. It's harder to breakdown and holds up longer.

The first pics are of my film and my printer using WB sharp edge coated screens.

The imagesetter is at the shop I'm doing screen work for. He's an old school camera dark room guy who after a fight with a vellum print ages ago, said screw it and bought a 65k inline processor and never looked back. It's paid for itself twice with the amount of film output he used to farm out before the thermal printers hit the market. Now that ink jets are priced so everyone can use one, true silver based processors aren't even a thought in peoples minds. I hope to own one someday as with one, the only thing you have to do is burn through the film.

That smooth surface, RZ value is almost glass like on the 150 screens that we use for white base prints. thicker base with thin top colors so we keep the high mesh thin coated. I have to keep reminding the press op's to take off squeegee pressure as the tensions are starting to come up, the screens are now made perfectly and the EOM is back on track.

[blue moon]

after seeing the really, really nice halftones John made, I had to go and check to see what ours look like. It's been a while since I took a microscope to them and was curious what I'd find. I was pleasantly surprised, we are doing OK!

pierre

p.s. epson 4800, WP film with AccuInk ink. sorry for the blurry pix, but it's the best I could do. . .

[Dottonedan]

That does have great image detail, especially for what yours using, (as in not an imagesetter). I would say, though that I think the both of you could use even more thickness to that emulsion layer (base don top shots only).

That doesn't really mean more coats, but maybe just a slower last coat.  If I were coating screens, I'd give both of you another thin coat on top of your normal procedure.  My personal goal is to not just get clean edges and well defines cels, but to also raise that wall for a more defined hardy dot with some body (for opacity.....unless, you are really trying to lay down very thin layers of ink for transparency sake so they blend better.  That idea may also require one or more additional screens to get a better, more robust tonal range in the image. Using all thin layers some times does not give you that PUNCH we need in art colors. It can look more washed out.

As I've mentioned to you before, A thicker coat might help with better coverage on the base whites, as in only one stroke. You did make them a little thicker than you started out with, but I'd do a tad more. Just say'n buddy.

Did you ever get a EOM thickness gauge in use? I'll bet you're just shy of what your emulsion co recommends per mesh.

[jsheridan]

Nice grids you have there! Great detail and the edge def looks good.

That does have great image detail, especially for what yours using, (as in not an imagesetter). I would say, though that I think the both of you could use even more thickness to that emulsion layer (base don top shots only).

That doesn't really mean more coats, but maybe just a slower last coat.  If I were coating screens, I'd give both of you another thin coat on top of your normal procedure. 

Did you ever get a EOM thickness gauge in use? I'll bet you're just shy of what your emulsion co recommends per mesh.

Yes we both have low RZ values and could benefit from different coating techniques and or different emulsion.
I've done thickness coating tests on face-coating, We got far better results from adding another wet coat than face coating.

Let  me introduce another wrench to a socket party, we introduce viscosity into the puzzle. Each brand of emulsion has a different viscosity. Example is my 925WR and ChromaBlue. One is like water, the other like syrup. A 2x2 coat will yield different results when you measure EOM. I would prefer to add a wet coat with an emulsion that isn't to thin nor to thick for a range of mesh counts and build my desired EOM. Diazo based emulsions require you to add water and mix. Water reduces viscosity, so you can control, to a degree, the viscosity of the emulsion by weighing the water on a scale before mixing and tracking it's coating ability. You can use less water for the low mesh to avoid sag in the drying process and more water to get a better flow for high mesh screens. I have used different emulsions in the past with different solids content to coat say a 150 vs a 305 mesh with great results.

[Screened Gear]

Yes we both have low RZ values and could benefit from different coating techniques and or different emulsion.
I've done thickness coating tests on face-coating, We got far better results from adding another wet coat than face coating.

Let  me introduce another wrench to a socket party, we introduce viscosity into the puzzle. Each brand of emulsion has a different viscosity. Example is my 925WR and ChromaBlue. One is like water, the other like syrup. A 2x2 coat will yield different results when you measure EOM. I would prefer to add a wet coat with an emulsion that isn't to thin nor to thick for a range of mesh counts and build my desired EOM. Diazo based emulsions require you to add water and mix. Water reduces viscosity, so you can control, to a degree, the viscosity of the emulsion by weighing the water on a scale before mixing and tracking it's coating ability. You can use less water for the low mesh to avoid sag in the drying process and more water to get a better flow for high mesh screens. I have used different emulsions in the past with different solids content to coat say a 150 vs a 305 mesh with great results.

I was wondering if the viscosity of the emulation would come up. I use Aquasol HV and it is alot runnier then I like when I get it. I have been keeping it in a refrigerator and then it is alot easier to coat but also gives you a thicker stencil. I am interest to see if anyone else does this?

[alan802]

Yes we both have low RZ values and could benefit from different coating techniques and or different emulsion.
I've done thickness coating tests on face-coating, We got far better results from adding another wet coat than face coating.

I've done the same experiments on face coating and came to the same conclusion.  I wonder how many people are wasting valuable time with face coating?  I'm not saying face coating shouldn't ever be done but if you're trying to build a thicker stencil then you are wasting time and money without a doubt.  My personal opinion is that face coating is only needed for the upper echelon printing techniques and maybe some award winning print attempts.  The stencil thickness after face coating is almost non-existent and using a good emulsion and coating wet on wet is a far superior technique to building your stencil than face coating.

[ZooCity]

The stencil thickness after face coating is almost non-existent

That's the idea I think.  Face coats don't really up the EOM but will up create a smoother surface on the side of the screen you face coat.  It basically fills in the valleys and skims over the peaks created by the mesh knuckles. When doing detailed work I might coat a 330/30 1/1 with the thin edge of the coater and face coat to get that nice stencil wall without adding so much EOM that I lose the ability to resolve the finer dots and detail in both the exposure and when actually printing. 

Someone mentioned having too deep of a "tunnel" to achieve a good print and this could occur with like a 3% dot getting resolved but having trouble clearing fully.  Or, maybe it clears perfectly but you have an ink deposit that is too tall and results in excessive pickup and smearing when printing WOW. 

[alan802]

I think a lot of newbs and maybe even some vets might think face coating is done to help build EOM...I know the first time I read about the technique I thought it was to build up EOM.  I can see how with the really top end printing that flattening out the surface of the stencil can make a difference, but 99% of what we all do on a regular basis would not benefit at all. 

[Dottonedan]

I think a lot of newbs and maybe even some vets might think face coating is done to help build EOM...I know the first time I read about the technique I thought it was to build up EOM.  I can see how with the really top end printing that flattening out the surface of the stencil can make a difference, but 99% of what we all do on a regular basis would not benefit at all.

I'll have to respectfully disagree with that last statement.  It does affect you all every time. The difference is, the improvement on image quality is not as noticeable (on the surface) for most of you to add the extra work. It's the optimum method. Most are saying that they are satisfied with the less than perfect and that's ok also.

You can think of the goal and benefits as being similar ( if not the exact same as) using capillary film. Same benefits all around, direct emulsion is cheaper in the long run.

People who use Cap film say they go through the added labor and hastle for the image quality. You get the same results by coating with an accurate EOM and face coating. Cap film is pre designed and sold in different thicknesses just like we are talking about with the goal of our coating techniques.

Thick enough EOM and a smooth surface to form a proper gasket. When we say 90% of our printing doesn't need that, I would disagree. My 110 mesh coated properly is going to provide a better image edge and first time opacity that with someone elses 110 that shows hills and valleys of knuckles.  That part is all math and not just skill.



D

[alan802]

I guess what I meant Dan is I believe that proper eom is important all the time, but I don't believe face coating is necessary to achieve proper eom.  And I don't think you need to face coat to achieve a smooth enough surface to print properly.

[blue moon]

That does have great image detail, especially for what yours using, (as in not an imagesetter). I would say, though that I think the both of you could use even more thickness to that emulsion layer (base don top shots only).

That doesn't really mean more coats, but maybe just a slower last coat.  If I were coating screens, I'd give both of you another thin coat on top of your normal procedure.  My personal goal is to not just get clean edges and well defines cels, but to also raise that wall for a more defined hardy dot with some body (for opacity.....unless, you are really trying to lay down very thin layers of ink for transparency sake so they blend better.  That idea may also require one or more additional screens to get a better, more robust tonal range in the image. Using all thin layers some times does not give you that PUNCH we need in art colors. It can look more washed out.

As I've mentioned to you before, A thicker coat might help with better coverage on the base whites, as in only one stroke. You did make them a little thicker than you started out with, but I'd do a tad more. Just say'n buddy.

Did you ever get a EOM thickness gauge in use? I'll bet you're just shy of what your emulsion co recommends per mesh.

no EOM yet, just purchased moisture meter for the emulsion, still looking for a good deal on the EOM meter. . .

We are sort of dialed in with what we are doing and it will take quite a bit of work to make any changes no matter how slight they are. Having the EOM meter would be the first step as trying to quantify something without the ability to measure it is a fools errand. We could poke and guess and play, but we would be guess as to what we are doing. So meter first, than a little more research and few phone calls then some testing.

I would also like to point out that our stencils look good because we had Dan on site to work with us and make them look good. Anybody wanting a significant improvement in a short amount of time should really consider hiring Dan. Yes, I am pushing his services, but not because I have any stake in it, but because it worked for us and should work for most others.

pierre

[blue moon]

I guess what I meant Dan is I believe that proper eom is important all the time, but I don't believe face coating is necessary to achieve proper eom.  And I don't think you need to face coat to achieve a smooth enough surface to print properly.

I think the point made here is that there is always a better way to print, but we have to use what is good for business. If 99.9% of our work does not warrant the face coat, there is no point in doing it on all the screens. The 0.01% that does, we can spend the extra time and do it.

pierre