Spot Color for Screen Printing

Creating spot channels:

Process color separations are films (often called "printers") used to print a full color image. These four sheets of film have been separated into their individual color channels so they'll print properly using CMYK inks (Cyan, Magenta, Yellow and Black). Of course this is a highly simplified definition.

Spot color separations are films that do not necessarily use the full color image to derive the image value which will be used. Spot color is usually designated by the designer or artist. Spot colors do not come from Process Color Separations unless they are added as separate, individual pieces of film.

For screen printing, we assume you mean "Spot" color. In this case you'll need an individual "Spot Color" and its corresponding sheet of output film in order to burn the screens and print the T-Shirts.

For each color you wish to (screen) print, you'll need to create a new spot channel or convert an existing alpha channel to a spot channel.

To create a new spot channel:
1. Choose Window > Channels to display the Channels palette.
2. To fill a selected area with a spot color, make or load a selection.

Now do one of the following to create a channel:
* Ctrl-click (Mac OS: Command-click) the New Channel button in the Channels palette.
* Choose New Spot Channel from the Channels palette menu.

You will see a new Channel icon appear at the bottom of the Channels Palette, with your selection

If you made a selection, that area is filled with the currently specified spot color.

You'll need to assign a color to this channel. 
* Click the color box, and choose a color (Select from any of the color systems included with your Photoshop program. If you create your own custom color, don't worry, the screen printer can mix up the ink color you need.

We do not know if you'll be using transparent inks, but if you are not then use a value of 100% to simulate the opaque silk screen inks. The channel can have grays and gradients of the ink, however you need to make sure the film will be output at the screen frequency required by the screen printer.

KEY RULE: You MUST give each Spot Color Channel a unique name. This signals to the software that it is not a process color, and that it must be imaged as a separate piece of film.

TIP: it helps to name the channel the color you'll be printing.

Converting existing channels to spot channels:

If you have edited and modified one of the existing Process (CYMK) channels for use as a Spot color, then do one of the following:
* Double-click the alpha channel thumbnail in the Channels palette.
* Select the alpha channel in the Channels palette, and choose Channel Options from the palette menu.
2. Rename the channel (Again this is important)
3. Select Spot Color
4. Click the color box, choose a color in the Color Picker dialog box, and click OK. Do NOT pick the same color again. You don't want two films of the same color.

Finishing:

Before outputting proofs or films, you need to know the screen process your printer will be using. Some substrate stencil processes use a film positive, others a negative. Consult your printer.

Choose Image > Adjustments > Invert to apply the color to the selected area of the channel.

REMEMBER: you can edit those channels using brushes, type, etc. so long as you stay to black and white ONLY.