To overprint all black in your artwork, select the Overprint Black option in the Print dialog box when you create color separations. This option works on all objects that have black applied through the K color channel. However, it does not work for objects that appear black because of their transparency settings or graphic styles.
You can also use the Overprint Black command to set up overprinting for objects that contain a specific percentage of black. To use the Overprint Black command: