ILLUSTRATOR OVERPRINT

[boom]

I want to color many vector's elements in Illustrator for placing in
Indesign - in 2 color project. I want to use the overprint feature in
Illustrator for this goal, but I don't know if I'm on the right way. On my
project I use the 2 colors: black + panton (spot orange), I color some
parts of the vector's with gray (shade of the black), duplicate it and
color the topmost part with shade of the panton (spot orange), and set it
to overprint, so the lighter part (color) set to overprint. I'm not sure
if that's he correct way to use the overprint feature, if I have to put
the lighter part or the darker part on topmost and set it to overprint. I
saw an option: "image map" - in the window of the Attributes options (for
overprint settings) but I don't know If I have to use it for overprint
settings, and how do I have to use it.

[David]

From Illustrator Help:

About overprinting
By default, when you print opaque, overlapping colors, the top color knocks out the area underneath. You can use overprinting to prevent knockout and make the topmost overlapping printing ink appear transparent in relation to the underlying ink. The degree of transparency in printing depends on the ink, paper, and printing method used. Consult your print shop to determine how these variables will affect your final artwork.
You may want to overprint in the following situations:
Overprint black ink to aid in registration. Because black ink is opaque (and usually the last to be printed), it doesn?t look much different when printed over a color as opposed to a white background. Overprinting black can prevent gaps from appearing between black and colored areas of your artwork.
Overprint when the artwork does not share common ink colors and you want to create a trap or overlaid ink effects. When overprinting process color mixes or custom colors that do not share common ink colors, the overprint color is added to the background color. For example, if you print a fill of 100% magenta over a fill of 100% cyan, the overlapping fills appear violet, not magenta.
After you set overprinting options, you should use the Overprint Preview mode (View > Overprint Preview) to see an approximation of how the overprinting colors will print. You should also carefully check overprinted colors on separated artwork using integral proofs (where each separation is shown in register on a single piece of paper) or overlay proofs (where the separations are shown in register on separate plastic sheets stacked on top of each other).

Also, If you don't like the way "overprinting" looks on the screen, you can use one of the transparency functions instead.
If you are designing a piece, then you can use the screen rendering as your guide, just do it the way you want it to look.

my .02,
David