Making Dots....

[T Shirt Farmer]

Post is directed at printing half tone films and screen making. I am wanting to sharpen my ability top hold a full tonal range, morie free using various line screens and mesh... my questions are...

Do you get a cleaner dot with per say a epson 4900 over and epson 1430?

Does one need to calibrate rip and does this require a densitometer, if so which one do you recommend?

Do you use a different emulsion than you would for line art, if so what product.

Using a step wedge when burning a screen, upon washing out I usually get 1 step that is almost falling of, the next one looks kinda solid and the 3rd is usually looking pretty strong. Should the wedge be placed on outer edge of screen or under a corner of the film thus representing how the frost on wp film effects the exposure.

How do I know if I am getting dense enough dots on my film?

Any comments are much appreciated!

Robert

[3Deep]

Robert your question will have many many answers, and the best answer I can give you right now is test, test & test....each shop has a set of rules that work for them that may or may not work for you.  What is your base of printing...your market?  that will help give you some good anwers from other members as we all do print, but have totally different needs and print styles.

Darryl

[cbjamel]

Post is directed at printing half tone films and screen making. I am wanting to sharpen my ability top hold a full tonal range, morie free using various line screens and mesh... my questions are...

Do you get a cleaner dot with per say a epson 4900 over and epson 1430?

Does one need to calibrate rip and does this require a densitometer, if so which one do you recommend?

Do you use a different emulsion than you would for line art, if so what product.

Using a step wedge when burning a screen, upon washing out I usually get 1 step that is almost falling of, the next one looks kinda solid and the 3rd is usually looking pretty strong. Should the wedge be placed on outer edge of screen or under a corner of the film thus representing how the frost on wp film effects the exposure.

How do I know if I am getting dense enough dots on my film?

Any comments are much appreciated!

Robert

I agree with what market, but also what emulsion you are using to what you use as an exposure unit, what rip and printer. It all matters to as you as close to correct as possible.
Shane

[Gilligan]

I'm tuning into this as well.  I'm just about to start playing around with some halftone work.  I have my own question that I need to bring up but I'll start my own thread.

[Screened Gear]

How do I know if I am getting dense enough dots on my film?

When you wash out your screen if the open areas come off in sheets your film is not dark enough or you are over exposing. The emulsion should just melt away in to the water, maybe a little chunky. This is really a balance of your exposure time and the density of your film. You want to expose your screen just right. The lighter the film the shorter your exposure time has to be to wash out your screens. To hold very fine dots you have to fully expose the screen without hardening the design area. This is why a very dark film is important. With lighter films you will harden the design just a little (or for some alot) when exposing the screen. This makes the screen harder to wash out. It takes longer and needs more pressure to open up the slightly hardened dots or wash out around your small stand alone dots. This added water, time and pressure makes it easier to lose that detail.

Another test I came up with to see densities quickly: hold the film up to a light so your looking through the film in a printed area. Put your finger between the light and the printed ink so your looking at your finger through the ink. The part where your finger is represents 100 percent black. What percent is the other area. I have done this test lately to check if my changes to my rip is improving the darkness and by how much. I have got it so dark that I can verily see my finger outline. I started out at about a 50% difference. I know its an over kill at that dark. Now I just have to print some films and make screens to see where the sweet spot is with my exposure time.

Over exposing is just like not having dark enough Film. You should make sure your not over exposing. The only real test that I have found that makes sense is the white glove test. If you expose a screen and the squeegee side has emulsion wash off your under exposed. If you can take a white glove or anything light color fabric and wipe the squeegee side of the screen when washing out and no emulsion color comes off your fully exposed. You want to do this test to find the high exposure time and low exposure time to make sure your exposure time is right.

Film density and exposure time are the first step in my opinion to doing high end prints. Master this and then move on to calibration for densities and dot shape. If you can't hold the dots your densities will not Matter.

Sorry for the rambling I have been messing with this alot lately and I wanted to share my findings.

Jon

[tonypep]

Your vendors should be able to provide you with a step wedge film to test exposure and the better ones will stop by and show you how to do it. You can also make one of your own. There is a characteristic of film postives known as the D-Max to D-Min Ratio. D-Max is the density of the ink on film and D-Min the transparency of the film itself. All are not created equal. Obviously you want the densest black on the clearest film for best results. A densitometer can accurately measure this. Some companies like Ulano have offered to measure this for me from time to time. Remember to ask nicely though. Once you dial this in be careful when switching variables like emulsion or coating techniques. We use a pressure washer that is adjusted for mild PSI to ensure we're getting everything but that's not always necessary.
Heres a simple fade from red to yellow to blue to magenta, the green, purple and orange secondary colors are created with 65 dpi dots in discharge.

[Sbrem]

A pretty deep subject. I started by reading as much as I could about what a halftone is, and how it was created using film and halftone screens and a process camera. Of course, no one does it that way anymore, but the theory is the same; a percentage of black and white forming together to make a gray. Forget about color at first, just learn to make a good black and white halftone, after that, it's just doing the same thing for each color. You should learn what dynamic range is, compared with the tonal range that you can produce, and how to make them match up. Go slow, and practice. Dots from an inkjet printer are OK, but you need to see real imagesetter dots to know what a clean dot should look like. After you make a good film, then you need to test to make a good screen; the mesh you want to use may determine your linecount and angles, or the other way around! Lot to learn here, but be patient, the time goes by anyway.

Steve