SCREEN PRINTING

The following instructions and procedures are meant to be used as a general guide in creating Four Color Process separations to be used for screen-printing on textiles.  The parameters are generalized and each artist would use their own judgment to determine the outcome of the finished piece.  Make sure you document all adjustments so if you end up with pleasing results, you know to make similar adjustment the next time.  Expect to rework any set of separations at least once and probably more than that when first starting out.  The documentation will help when deciding what adjustments are necessary on the rework.  The adjustments made for this article are done in Photoshop 6.0.  If you are using a different version, the information will be the same, but the settings may not be located the same places.
Make a duplicate of the original so we can check against it as we go through the separation procedure.  Our goal is to end up with a set of separations that look like a weak or washed out version of our original.  We want this because of the dot gain we will experience when we print.  If out finished separations look great on the monitor, then our print will probably look muddy.
            Image
                        Duplicate…
Next we need to address is the resolution.  We would want to work with a resolution that is approximately 2-2 ½ times the LPI or halftone size (number of dots per linear inch) we will use in our output of the separations.  Since most shops work with a45-65 LPI, our resolution should be between 100 and 150.  If the resolution is too high, some of the information might be too fine to hold when we output the information and will be discarded by the program. 
            Image
                        Image Size…
                                    Resolution
            We need to make sure we are in CMYK.  If not, go to
            Image
                        Mode
                                    CMYK Color
Although our artwork is now separated, it is separated for the offset process, since Photoshop was written for the offset trade.  If we use the separations the way they are, we will probably get a muddy print.  Because of this, we have to modify many of the parameters.
            Making adjustments so the image will have a little more life is done as follows:
            Image
                        Adjust
                                    Brightness/Contrast…
I like to brighten my image a little and then increase the contrast so my light areas jump forward and my shadow areas drop back, but I don’t loose detail.  Often, my colors become more intense and make the image more appealing for a t-shirt.  Once satisfied with the results, hit OK.
            We are now ready to adjust each of the colors and compress the dot range so it is suitable for screen-printing.  It will be necessary to take the information that is less than 15% and more than 80% and compress them towards the center to our usable range.  We will still have information that is less than 15% and more than 80%, but the bulk of that information will sit where we can use it.  The reason we do this is because holding dots that are less than 15% for most printers is difficult.  Dots of over 80% will probably print as a solid area due to dot gain or dot spread.  By compressing the range, we will have a very usable set of separations.
            Image
                        Adjust
                                    Curves…
Do not make adjustments with the CMYK showing.  Go to the arrow at the right and choose the Yellow.  Take the bottom of the diagonal line and move it to the right until you see 15%.  Now take the top of the diagonal and pull it down until it reads 85%.  Do the same to the Magenta and Cyan.  There are times when less of an adjustment will be needed and it will be up to each artist to make that decision.
            Next, we have to make adjustments on the black, which is the K.  Because the black is very strong, it wills over power the other colors unless we make a more dramatic adjustment.  We also only want black in the darkest shadow areas so choose the Black and slide the bottom of the diagonal up to 30% and pull the top of the diagonal up to 70%.  If you feel you have lost too much information, back off the amount of compression.
When the Preview button is hit, you will be able to see how much of an adjustment was made.  If you are unhappy with the results, go into the history and delete that which you are unhappy with and make new adjustments.
Now we have to add some information and make several additional adjustments.
File
            Page Setup…
                        Screens…
Remove the check mark next to “Use Printer’s Default Screens” so you can choose your own Frequency (LPI/Half-tone) and insert that frequency.  For manual printers, I would recommend 45 and for automatics 55.
            Next, change the Shape to Ellipse.  An ellipse have a little less dot gain and more surface so it will be a little easier to hold on a screen.
            We are now ready to address the Angle.  Working with the given angles will be difficult since the Black is at 45 degrees and the dots will sit on the horizontal strands of mesh and could easily create a moiré or saw tooth.  The Yellow is 90 degrees and would sit on the vertical strands and could also create a moiré or sawtooth.  By changing the angles 2-4 degrees, we may avoid these problems.
Color               Offset Angles             Screen-print Angles
            Yellow                        90 degrees                               86-88 degrees
            Magenta          75 degrees                               71-73 degrees
            Cyan                60 degrees                               56-58 degrees
            Black               30 degrees                               26-28 degrees
Most screen-printers will have three colors that print well and one that always seems to moiré.  Since we are not interested in creating a rosette pattern as offset printers are, we are not forced to use all different angles.  For example, if the Magenta seems to be the color that usually has a moiré problem, we can eliminate that angle (71-73 degrees) put the Magenta to the 86-88 degree angle, move the Yellow to the same angle as the Black (26-28 degrees) and not have a moiré problem.
            Another possible solution to the moiré problem is using only one angle for all colors.  I like to work with a 50 LPI with a 61 degree angle for all colors.  Test a variety of angles on various mesh sizes with the LPI you will be using and select the angle the seems to have the least probability of moiré.  Since the rosette pattern is not important to us, this will also work.
            Once the Frequency, Angles and Shape have been selected and OK has been hit, we need to select a few more items in Page Setup.  Check the Calibration Bars, Registration Marks, Center Crop Marks and Labels, then hit OK.
            We will need to make further adjustment to our image before we can print the separations.  Go to
            Edit
                        Color Settings…
                                    Settings:
                                                Custom
Working Spaces
            CMYK:
Hit the arrow and go to
Custom CMYK
Once in that screen, go to
            Name:
Change to Screen-print, then go to
            Ink Options
                        Dot Gain:
36%
Some printers can use a little less dot gain and others more.  This is only a starting point.  If you print with a lot of pressure, increase the dot gain and if you use a minimal amount of pressure, decrease the dot gain.  Printers will not use less than 25% dot gain due to the nature of the inks we use and the process itself.
In the same screen, go to
Separation Options
            Separation Type:
                        UCR
Under Color Removal is the taking away of color from where the black will print so there will be room for the black.  Without UCR, the black areas could turn brown.
Still in Separation Options, go to
            Total Ink Limit
                        250%
Enter OK until you are out of all screens.
You are now ready to output film, print a sample and see what adjustments are ne