We will trap the sample we did in Spot Color Knockout and then change the percentage of the Spot Color for print. If you don't have the sample we did in the Knockout tutorial, go do that one and then continue here.

1

Whenever you have two colors which vary as much as these do you'll need to trap them. The knockout we made and the spot color are the exact same size. If the press gets the registration a tad off (which almost always happens) you'll have a white hairline showing through.  To solve this you need to either make the knockout a bit smaller or expand the spot color.

We are going to expand the spot color. Don't even try to use the trapping that Photoshop has because it won't work in the Spot Color Channel, you have to do it manually. It isn't all that difficult.

Most offset printing applications require about .25 points of trap. There are 72 points in an inch. To determine how many .25 points there are in an inch, divide 72 by.25 which is 288.

Now we need to determine how to get this into pixels. Divide your resolution (ours is 200) by 288. Multiply the result by 2 and round off to the nearest whole number to determine the stroke width. (always round up)

Based on our calculations above we need to stroke 2 pixels

CTRL+Click (Option+Click) on the Spot Color channel to select it.

Be sure you have your foreground color set to the color of your Spot color, so the stroke is the same color.