films for screenprinting

7/25/2019 Films for Screenprinting

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Options for Creating Films

1. Hand drawn images on frosted mylar, or tracing paper.

2. Oiled photocopies, laser prints, or inkjet prints of drawings,

photographs, collages and appropriated material.

3. Inkjet transparencies printed from files created in Photoshop or

Illustrator.

Working with Frosted Mylar or Tracing Paper

The following materials work best for hand drawing opaque images:

Micron Pens, India Ink, China Markers, Litho Crayons, Black Acrylic

Paint, Technical Pens

After you complete your drawing it is best that you draw over it a second

time to assure that it is opaque enough to block the UV light from exposing

the screen. It is better to make your drawing heavier and darker than you

want, to assure that it does not print light, spotty or have lines that will

disappear.

For color separations, cut one sheet for each color to the size of your paper

The sheets can be placed over a template on newsprint noting the imagesize and composition of the print as a guide for drawing the separations.

The Mylar sheets can also be punched and registered with registration pins.

Working with Inkjet Printers

Inkjet printers produce very fine photographic images by spraying tiny dots

of water-based ink onto the paper. These dots are far too fine and delicate

to block ultraviolet light when exposing your screen, or to be held in the

comparatively coarse mesh of the screen. To assure that the dots are large

enough, and opaque enough, your image must be adjusted in Photoshopbefore printing it to film.

To help you visualize this, think of the screen mesh as a sieve: If the image

dots on your film are finer than the screen mesh, they will not be held in the

mesh to print later.

Kevin Haas | kevinhaas.com/printmkaing

Screenprinting

Creating Films for Screenprinting
http://www.kevinhaas.com/http://www.kevinhaas.com/


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The most common method for translating a continuous tone photograph or

other image with varying tonalities into a printable image, is to convert it into

a halftone. The halftone pattern is a grid of varying sized dots that create the

visual illusion of different tonal values. When properly printed on an inkjet

printer, the halftone dots will be opaque enough to block the ultraviolet light

used to expose the screen, and large enough that they will be held acrossseveral threads of the screen mesh.

Although converting an image into a halftone in Photoshop is easy, it is

important to determine the correct size of the halftone dots for the screen

you are using, as well as the angle of the halftone grid so it will not conflict

with the grid of the screen mesh creating what is called a moire. Moire is the

dreaded scourge of the screenprinter: It occurs when two grids overlap in

such a way that they create rippling patterns in your final print. The settings

listed below, should help you avoid this problem, but testing and

experimenting are often necessary.

Creating a Halftone Bitmap

1. You will need a grayscale file that is at least 150ppi at the size you will

print it. This information can be checked by going to Image > Image

Size... in Photoshop.

2. Convert the image into a Bitmap: Go to Image > Mode > Bitmap. Set

your Output Resolution to 720 and Method to Halftone. The Output

Resolution should be your lpi x 16, and evenly divisible by your printers

maximum output resolution. For example, a 35lpi halftone needs an

Output Resolution of at least 560, but 720 is the next higher resolution

that is the inkjet printers resolution of 1440 evenly divided by 2.

3. Print your file and expose your film to your screen.

It is best to use a transparency film made for inkjet printers and

screenprinting films. The best printer media setting to use for these films is

Premium Glossy Photo Paper on Epson printers. This will assure the

maximum density of black, and a printing resolution of 1440dpi.

You can also print your bitmap files onto lightweight inkjet paper that can be

saturated with baby oil to make them transparent enough to expose to your

screen. Epson Singleweight Matte, or other inkjet paper lighter than 120gsm

will work.

Getting more from Threshold

The Threshold setting in Photoshop is an easy way to create a high contrast

black and white image to use for screenprinting. But you will often loose

more information than you would like with this option. To pull more out of

images with Threshold, create a Threshold adjustment layer, and then use

the dodge and burn tools on the image layer to bring back more information



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The dodge tool will help bring back details in the black areas, and the burn

tool will help add details in the blasted out white areas.

Posterizations in Photoshop

You can make posterizations in Photoshop at the click of a button, but to get themset up properly for screen printing takes a few more clicks. Posterizations work best

with grayscale files, and can be used to print the file in several grays or colors to

extend the tonal range of the image. Once your grayscale image is ready, complete

the following steps. When you set the number of levels, remember that one of them

is the white of the paper, provided that there is white in the image. This means that

typically you will have one more level than the number of colors you want to print.

1. Adjust the levels of your file to assure good contrast in your file. Go to Image >

Adjustments > Auto Levels.

2. To posterize your image, go to Image > Adjustments > Posterize...

3. Save your file as myimage-POSTER.psd (or anything that you can remember

later), to keep your original file unchanged. Now that the image has been broken

down into several values, you will need to extract each one to create a film to

expose your screen with.

4. Go to MB>Image>Adjust>Threshold. The space between the lines will indicate a

particular color with the darkest on the left and lighter colors on the right. Move

the slider under your first color to be printed on the right and click OK. Print the

image.

5. Go to MB>Edit>Undo Threshold or use the history palette (MB>Window>History

Palette) to return to the index color version of your file. Repeat the

Image>Threshold function to isolate the next color for printing. Keep repeating

these steps until all of your films are printed.

Numbers and Acronyms

ppi = pixels per inch (the resolution of your file)

lpi = lines per inch (lines of halftone dots)

dpi = dots per inch (pertains to printers)

General Formulas

optimal lpi for screenprinting = mesh 5. (approximately)

optimal resolution for halftone bitmap file = printer resolution 2

(For Epson printers this is 1440 2 = 720. This will avoid conflicts

between the file resolution and the printers resolution. Another way to

determine the resolution for a halftone bitmap is: lpi x 16. This will mean

that every halftone dot is created within a 16x16 grid of pixels, assuring

a maximum range of halftone dot sizes and apparent values.)



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Typical Halftone Screen Angles for Screenprinting

Black/Key Color: 22.5

Magenta/Medium Value Color: 52.5

Yellow/Lightest or very light colors: 82.5

Cyan/Medium Value Color: 112.5

These angles are different from offset printing screen angles, since with

screenprinting the angles 0, 90, and 45 must be avoided since they

will typically conflict with the screen mesh. 22.5 will usually work since

it is halfway between 0 and 45.

Remember

Laserprinters/Photocopiers = Halftone Dots and Plastic Toner

Inkjet Printers = Random Dither and Water-based Ink


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