Halfftones

[Catspit Productions]

I have to agree with Saati on both counts. Exposure time will vary depending on the above mentioned factors including the density of your film positive.

And yes, if you have to use too much pressure to washout a stencil then something is most certainly wrong. The emulsion ideally should dissolve and rinse out. If it is doing anything else then there may be semi curing issues due to poor film positives or too long of an exposure time.

Thanks Saati!

[ApeShirt]

So you both are saying a garden hose with a nozzle is too much pressure? I've seen video from screen printers and supply companies even use a pressure washer.

[Saati]

So you both are saying a garden hose with a nozzle is too much pressure? I've seen video from screen printers and supply companies even use a pressure washer.

In a "perfect world" standard line pressure (household/ residential water pressure) and a spray nozzle set to shower or cone spray is sufficient to develop the screen. If you have to use a pressure washer to develop one of 2 things are hapening you have over exposed and burned through your positive or your impatience is getting the best of you. either way the risk of loosing detail due to over exposure or blowing the details to peices due to the pressure are greatly increased.

Just because you see someone else doing it doesnt mean it is the right way. Don't you remeber your mama (no I am not making mama jokes) saying "if you see your freinds jumping off a bridge do you think you have to?"

[Catspit Productions]

That’s funny Saati. I always remember Mama!

But yeah a simple garden hose with a spray nozzle should be fine. If you find you are using excessive pressure or having a hard time washing out the stencil to where you think you need more pressure then there is something awry.

I use a standard garden hose with a spray gun nozzle attachment for washing out stencils. And even with that you have to be careful you don’t washout any detail if you get too close or you use a nozzle setting that directs too much pressure to a point.

AND it should take about 4 minutes or less to washout a stencil if all is right. Higher mesh counts should take a lot less time than lower mesh counts that hold much more emulsion.

But basically Saati and I are saying the same thing. You shouldn’t need much water pressure to washout a stencil. The emulsion should dissolve and rinse out so you shouldn’t need much pressure if you have your exposure times down and your film positives are very dense.

But many people do it many different ways and you’ll have to figure out what works for you. Even if you watch my videos and try some of my techniques you may find that you have to tweak your methods for your particular situation.

Does that make any sense?

[OffsetnScreen]

Good stuff here apeshirt and jonathan, As a newbie, i now feel like i may have bitten off more than i can chew on my first t-shirt run that I have taken on. Pocket side is easy solids only. The image was furnished as a full color file and I cropped out a guitar and amp and ran some photoshop effects on it and added the type. I asked a girl ..by text msg...who knows screen printing what I needed to do to prepare the halftone properly....you're gonna love this. she sent me a catspitprodctions link to read...I went back and re-read the article and saw where there were references and a chart of screen mesh counts to use, however the moire issue wasnt resolved for me. I know there must be some mathematical correlation between the dpi of a rastered image and the dpi output of the imagesetter or film positive output device but how it intertwines with line screen frequency and screen mesh count to produce at a particular angle to avoid when burning the screen is a bit beyond what I was able to grab from the article..I did get some fresh emulsion today ...I haven't opened it or read the timetables...its a premixed type from tubelite. The halftone I will send out ...hint hint...and I will work with my 4 yr old plastisol on the shelf at making it creamy...
Does the halftone have to be converted to a vector file for the film positive output device?? The whole idea of a rip I thought, was as a "raster image processor" I can see where software would bog down and make for long rip times,having to convert from vector to raster, however if you are dealing with the halftone as a raster image to begin with, wouldn't that make the rip's job easier therefore quicker output time?

[Catspit Productions]

That’s funny. Catspit is everywhere;

Normally the moiré is resolved by angling the dots. This is true only when there is a particular given. The screen mesh needs to be stretched perpendicular to the frame edge. Because the screen openings in the mesh are square we assume when the screens are stretched properly that the grid is also square to the screen frame. That way we can angle the dots on different screens to avoid a moiré.

If it’s a 1 color halftone you can use a 5 degree angle. We may use angles like 5, 10, 15 and 20 degrees for color halftones that are not CMYK. For detailed halftones in CMYK we may follow the suggestions in the article you were most likely linked to as you mentioned:

http://www.catspitproductionsllc.com/halftone-tips.html

I think most screen printers use round or square halftone dot types. So in this case we get screen angles relating specifically to the colors in the original image. You can see that the separations themselves are very important to the final print result. You also need to make sure you use a high enough mesh count with an excellent emulsion which will allow the mesh to hold the dot. By the way the dot can even be rotated physically on the screen to avoid moiré but the challenge there is registration of all screens.

RIP software makes a non postscript printer print dot. I don’t know anything about the speed issue. But I know I cannot print halftone dots I need to make film positives on a standard inkjet printer without it. Normally we output from Illustrator in my shop and go direct to the printer for spot colors and we use RIP for the halftone jobs. Speed is not the concern here.

Illustrator has massive output capabilities and if used properly even is said to have post script abilities. I have no idea if that is true because I am no professional graphic artist. I’m the printer.

[OffsetnScreen]

I found an excellent article I would like to post a link to concerning halftones and moire that I thought might be interesting....if the posting is a nono, then i must have missed it in the forum rules and my apologies...
http://www.signindustry.com/screen/arti ... Moire.php3
Hope this helps....back to study hall for me...peace out...
neil

[ApeShirt]

That is an excellent article. Thanks for sharing it.

[OffsetnScreen]

I have yet to come across the info on how to post pics, I cant wait to show yall the halftone I did. I engaged a local screen printer to make my halftone and I left it to their prepress department to decide what mesh count to use for the screen and what line screen frequency to output the positive stencil at. I expected a new screen, but ended up with a used 156mesh that had my image on it. The image looked sharp. I noticed the thinness of the emulsion coating ...much less than I had coated at..I noticed 3 strokes of emulsion that they used. I am looking at an inkjet output device by Epson, the 1430 which Epson has now on sale at 250.00. Their software will not make a halftone dot and will not provide Postscript L3 support. Epson directed me to look for a third party vendor and I found more than one. Accurip is one and iproof systems is another that comes to mind. iproof systems is out of the Titusville/Melborne Florida area and I recall them as being Formerly Known as Birmy Software. They were one of, if not, the first small software company to produce Postscript compatibility for ink jets, specifically Epsons, and have been doing it longer than most. I spoke with Ted, the owner about his softwares capabilities, and he told me of several advantages that his Postscript RIP has over the Accurip software. Traditional as well as schochastic halftone screening is available with his software. He was very informative and could probably write a book about ink-jet halftoning and was more than willing to answer my questions about the software and the way it controls the Epson 1430 in particular. A link to his site is http://www.iproofsystems.com/
There is a continuous inking supply system available for this Epson1430 which Power Rip Screen Print software will control under Postscript L3 that will save ink without having to go with 6 black cartridges.

[Catspit Productions]

Here is the post on uploading photos:

http://www.catspitproductionsllc.com/fo ... =35&t=2202