When printing on metal or transparent material, a white ink is necessary to create a white background. This acts as a neutral base that allows the other inks printed on top to have the correct appearance. Depending on the parameters you set in the White Underprint dialog box, the system automatically adds a white underprint to the area. This object will be put on a separate Illustrator layer for easy modification or deletion.
When the White Underprint objects are created on a separate layer, they will appear as a solid overlay because they are overprint objects. However, by default, Illustrator doesn't preview overprints. To see what the White Underprint objects will look like when printed, use one of these methods:
Important: The Ink Manager must be updated before using this tool.
In the White Underprint dialog box, set the parameters for the white underprint.
|Distance||Sets the width of the spread or choke of the underprint. Type a positive value to execute the underprint in spread format. Type a negative value to execute the underprint in choke format.|
|Underprint ink||Select the ink used for the underprint.|
Set the corner-point shape of the trapping area. Options include:
When choosing the Miter option, it is necessary to set a parameter for the Miter Limit.
Use this option to change the corner to a mitered (pointed) tip or to a beveled (squared-off) tip.
If the length value of the trapping area mitered tip is greater than Miter Limit value × Width of trapping area, it will result in a beveled tip. If not, the result will be a mitered tip.
|Ignore Ink||This parameter means that the underprint will not be executed when the object's ink color is selected.|
Ignore object which contains ignore ink: the underprint will not be executed when the object selected contains ignore ink;
Ignore object which only contains ignore ink: the underprint will not be executed when the object selected contains only ignore ink.
|Ignore White Area in Art|
If an art object's CMYK value is 0 and this check box is cleared, the art object will also be included in the white underprint effect.
If the check box is selected, the white underprint effect will not occur for this art object. The image shows the effect of selecting this check box. The center area that has no inks will not generate a white underprint.
|Ignore White Area in Image|
If a raster image object's CMYK value is 0 and this check box is cleared, this art object will also be included in the white underprint effect. If this check box is selected, the white underprint effect will not occur for this raster image object. The image shows the effect of selecting this check box. The center area that has no inks will not generate a white underprint.
Adjust Underprint is used to create an "On-Center" effect for the white color block and non-white colorblock of the underprint's border.
For images with Alpha channel and Opacity Mask, the Image Underprint setting can preserve the original opacity effect and the underprint will be image.
|Gradient Underprint||See the Gradient Underprint section below.|
After setting the parameters, click the execute button in the lower-right corner of the palette.
Note: Multilayer gradient or overprint objects cannot support the gradient underprint function.
To get the gradient underprint effect, the gradient objects must meet one of the following three conditions:
|The gradient has a white-color (CMYK=0) stop point.|
|The stop point of the gradient has opacity and there is no color under the gradient.|
|All stop points of gradient are the same and have a singe ink except their ink percentage.|
The processing principle of Gradient underprint is as follows: