Halftone printing is a type of screen printing method that emphasizes the use of shading with tiny dots. Pictures can be printed using halftone screen printing and only use one single color to do so. This process of halftone printing looks best when the one printed ink color is darker than the background.
To be able to screen print photographic or grayscale images, an image must be converted into what is known as “halftones”.
A halftone image consists of many small dots that make up the grayscale portion of that image.
Screen printing halftones can present certain challenges and we’ll address them in this tutorial.
HOW BIG A “DOT” SHOULD YOU USE?
The size of the halftone dot used will of course be determined by the type of artwork that you are going to print or the printing technique that you will use.
For example, screen printing on apparel typically involves printing halftones in a range of 35-65 LPI. There may be occasions where you want the halftone to be very noticeable and exaggerated for a special effects look, where you may want to go down to a 25 LPI size halftone which will produce a very noticeably large dot.
WASHING OUT HALFTONE SCREENS
As was previously noted, care must be taken when washing out any screen that contains halftones.
If your screen is exposed properly you should not experience any problems. Washing out a screen containing halftone dots should not be any more difficult than washing out any other type of screen.
COATING YOUR SCREENS FOR HALFTONE PRINTING
Use the sharp edge of the scoop coater for mesh counts of 162 and up. Most jobs involving fine detail and/or small halftone dots do not require a heavy ink deposit and you'll want to be able wash out the image on the screen easily. The sharp edge of the scoop coater deposits less emulsion on the screen resulting in a thin ink deposit on the printed product. For mesh counts of 162-305 and up put just one coat of the emulsion on the print side and one coat of emulsion on the inside using the sharp edge of the scoop coater.