4-Color Process Separations
When taking a design representation and attempting to recreate it with process inks, take these basic steps to make the printing process easier and more predictable on the press.
1. How can I create good 4-color process separations myself?
Start by creating CMYK separations with Adobe Photoshop. This program allows the user to load custom color values. The resolution should be 2.5 times the desired line count and the angles should be separated by 15 degree intervals.
2. Why doesn’t my print look like the on-screen image?
The four-color process is a very limited color gamut compared to RGB. There are some colors that are covered with pigmented inks that may not be covered with the default CMYK color values in your computer. Try preparing the image in RGB mode. If you receive a CMYK art file form an outside source, convert the color mode back to RGB when opening the file. This allows you to load your own CMYK color values later.
3. Why are my prints dark and muddy?
Dark and muddy prints are usually a direct result of incorrect color values in the program. If you use the default color values in Photoshop as you change the CMYK mode, you will have separations designed for paper printing. This color set is lighter and weaker than the pigmented process sets, resulting in too much information included on the cyan and magenta plates. To get on the right track, apply color values and convert your image to CMYK mode. The program can then separate the ink values you will be using on the press.
4. How can I give my print more depth and/or contrast?
In screen-printing, you are working with black and white gray scales to set the tone of the design. It is recommended that you set your white and black points. Your goal is to have some area in the design that is 100 percent black and an area that is 100 percent white. You may check the areas with your ‘info’ tool. If you do not have total black and white points, you may use the “levels” option to adjust the points.
5. How do I keep my flesh tones from looking “sunburned” later in the run?
As a print run progresses, the inks shear, causing a viscosity drop. As the inks flow quicker, you will experience dot gain. Even with correct color data and top quality inks, you must prepare for this. The use of a “wet white” is the best defense for this situation. The wet white is used on both light and dark shirts and will be printed before all wet-on-wet colors, allowing it to mix with them. The wet white should be a transparent white. This can be creating by blending a mixing white (like your mixing-system white) with an extender at about a 50-50 ratio. If you do not have a mixing white, a non-bleed white should be used. Do not use a bleed-resistant white, for it will build up during the print run.
6. How do I make a white plate for dark garments?
Use a white under base plate as you would with a wet white in l-a-b mode. Select the lightness channel, duplicate it, invert, but use curves to choke back the plate by only 8-10 percent. The base white is used on dark garments and will be printed first, then flashed and followed byt eh remaining colors wet-on-wet.
The correct rotation is: White Base – Flash - Wet white - Yellow- Magenta - Cyan - Black (You shouldn’t have to print Black on Black garments)
When printing with the under base white, it should resemble a gray study of the design, rather than a flat solid plate of white. Printing too much white, or having too much dot gain, can actually deplete the black (or shade) of the color space, limiting the color depth and range. This lays the foundation of the tints and shades of the design, creating a stark, crisp print. The halftone underlay will eliminate mottling and smearing, creating a clean, easy-to-print design.
7. Why does my black plate dominate the design?
The color theory behind this process is that the CMY portion of the four color process set is the subtractive of RGB. The black was added because of the inability of CMY to hit the darkest color shades. Black was never designed to be an equal partner in this process. The black plate should resemble a touch plate. To create this plate, adjust the black channel by selecting the black channel, select Curves, and then drag the left arrow to the right to the 25 percent mark. This knocks the black out of the 25 percent and lower gray areas, allowing the other colors to create the subtle grays. The design may appear light on the monitor, but trust that it will print darker.
This gives your printer the ability to apply more pressure to the print. This results in better color saturation as well as the option of having text on any one of the plates without the fear of “transparent type.”
8. How can I add a spot color without it dominating the design?
As mentioned earlier, the CMYK gamut is limited, so the addition of a spot color is very common. The two main considerations for using spot color are opacity and print rotation. The spot color should have no more opacity than the process set. Extend the spot ink to a point in which it is transparent in nature. This places the inks on an equal footing, making all of the colors effective in the design. The rotation will work the colors in seamlessly, creating an image that doesn’t appear “blocked out” with color plates.
Basic Steps for 4-Color Process
- Download the Photoshop spectral data for process inks and the Wilflex Tone 305 data.
- Get the following information from your production manager or contract printer:
• What Wilflex Process set are they using?
• What mesh count do they prefer?
• What halftone line count do they prefer?
- Scan, design or load the design into Photoshop in RGB mode. If you receive CMYK art from an outside source, the file will ask if you want to convert colors, select convert, then change the mode to RGB. You should not see any change in the appearance of the file.
- Set your white and black points quickly by converting to Lab mode, select the lightness channel, select Levels (command L). Switch off the preview box, and then hold down the Option key as you drag the left arrow to the right. The image area will appear completely white. Continue until you have a good black area showing. Do the same to the right arrow, until there is a good amount of white showing.
- While in this mode, create a base white or wet white, convert the image to Lab mode. Select the Lightness channel, go to the top of the Channel window, select the arrow, and select Duplicate channel. When the window pops up, name the channel, (White Base or Wet White) and check the “invert” box. Select Curves for white base; drag the left arrow to the right 8-10%, to simulate a choke. For a wet white, drag the arrow to the right until the color is only in the areas of the image are white and pastel colors. Convert the image back to CMYK. You will end up with the CMYK channels and the channel you just created. Select the channel you created, double click on it, double click on the color square then change it to white. Convert back to RGB.
- Do any adjustments, such as color balance, saturation, lightness or Filters now. Adjust the design to your satisfaction.
- In Photoshop look under "File" > "CMYK Setup". "Preferences"> "Printing Inks Setup". In the Ink Colors pop-up menu, choose "LOAD". Select the Wilflex Process ink set you are going to use (Process or Tone) and the mesh count preferred (305 or 355). Ex.- Tone 305 is the Tone color set through a 305 mesh.
- The set will load into the previous window showing the set name and dot gain @ 35%.
- Once this file is selected, it will remain as the Process set of choice until you change it or a new CMYK file converts it. Load the set into Photoshop > Goodies > Color Palettes, so that you know where to locate it at any time.
- Close the window, then convert your image to CMYK mode. This allows the program to separate with the inks you will be using and you should see very little change in the image when it converts. If there is a major shift in color, the image must have been out of gamut. See below for Out of Gamut images.
- Select the Black channel, select Curves, and then drag the left arrow to the right to the 25 percent mark. This knocks the black out of the 25 percent and lower Gray areas. The design may appear light on the monitor, but trust that it will print darker.
- Before sending the file to the output device, change the resolution to 2.5 times the desired line count. Ex. – 55 line would be 55 x 2.5 = 137.5. To convert to films, either separate out of Photoshop or split the channels and print them out individually.