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In printing, there is a concept known as overprinting and that basically allows you to determine how colors mix when they print on press. I'll give you an example of how you could actually control this directly from inside of Illustrator. I'm going to create a new print document. Let's click OK and take the regular settings here that are the default. I am going to go to the Swatches panel and I'm actually going to load up a Pantone color. So I'm going to go over here to this little Swatch Libraries menu, choose Color Books. Let's choose Pantone Solid Coated and just for argument say I come out over here, it's simple one, let's take Pantone Red 032. Let's just drag this over to my document and let's close this panel.
There may be times, for example, when you are working on a spot color job, maybe we're dealing with two colors. You want to work with black, plus the Pantone color. In this case, it will be Red 032. Now a lot of times when you are working with these different colors, if colors happen to overlap each other, how does that actually happen when that file gets printed? Let's take a look. I am going to create a rectangle here and then I'll create another rectangle right here. I'm going to select the top rectangle over here, which is actually beneath this particular rectangle right here, and let's go ahead and fill that one with Pantone red. I'm going to select this rectangle over here and fill that one with black and let's just get rid of those strokes all together on these objects.
So how will this actually print? If you think about it, I have a rectangle here which just kind of goes behind this black rectangle. If I would actually kind of run this through a printing press and I would actually run red ink on the paper first and then I'll put the black ink on top of it. If there is red ink that fills up the entire rectangle here, then in this area where these two shapes overlap on the paper itself, I'm going to get a mixture of the black and the red inks which will really turn this area of black to be even darker than it appears right now. Obviously when I look at this on a printed piece of paper, I'll see a darker area here than I will in the rest of the area of this rectangle. So because of that, the default setting inside of Illustrator and really in printing in general is that if an object is hidden from view, then the object in that particular area does not print at all.
In other words, this rectangle sits over here and this rectangle knocks out the area of the red rectangle behind it, which means another printing press when I actually create my plate, I have a red shape that looks like an inverted L shape right over here. Then I'd have this area here, which would be completely black, so there would be no red ink in the particular area at all. That's the default setting and that's what we refer to as a knockout. The objects in front knockout the objects beneath it so that way the ink itself is not mixed on the paper. However, there may be times when you do want the inks to actually mix on the paper itself. Think about it in this way, if I actually take this rectangle and instead of filling it with 100k, let's go ahead and fill it maybe with around 50% black.
Now if I were to actually go ahead and tell this particular object to not knockout the object beneath it, then there's a term that we use called overprint. In other words, print this ink over the ink that appears underneath it, so don't knock it out. Then what I would see here is a mixture of this 50% black and also the 100% red which would really give me a darker red. So what I'd be able to do is as a designer, I would be able to simulate different shades of colors. Right now I only have red and I have basically different shades of black, but this would allow me to using the ability to combine the inks on the paper itself to simulate darker shades of the red as well. So I really kind of end up having more color to work with.
The way that you would actually specify that as you would go to the Window menu and choose open up the Attributes panel here in Illustrator. With the object selected, I'm going to click on this option called Overprint Fill. Again, by default that's turned off, but now I have told Illustrator that when you print this don't knock out any objects beneath it, but overprint that particular fill so that the ink beneath it still stays. Traditionally, the problem has always been that while you can set these settings here inside of Illustrator, it's very difficult for you to preview what that's going to look like when it prints. In fact, even if you print it to your Inkjet printer or to your color laser printer, it does not show up on that output and that's because when you print to a composite proof, meaning what all the colors look like at once, the overprint commands are not applied. They only apply when you actually print separations out of your file.
In other words, the only real way to preview this would be to go down on Press and see as those sheets come out of the printing press. Therefore, Illustrator has a specific viewing mode and we can actually see or preview what your overprints are going to look like before you actually print your file. So turn that setting on, I'm just going to go over to the View menu here, I'm going to choose Overprint Preview. Overprint Preview is just a more sophisticated preview as it shows you what your artwork is going to look like when it gets printed on a printing press. Notice over here I see what this artwork is going to look like when the overprinting is applied and this is the area of the red that will actually print darker.
Now, many designers actually want to be able to use this effect in a creative manner. Meaning, even though I know that I only have two colors to work with, I may want to mix my ink to create a variety of swatches to use and therefore extent my options. For example, I'm going to delete this shape right here. I have this one rectangle. I will take this rectangle and I'll make a copy of it here, so now I have two rectangles. I'll now select both rectangles and I'll choose Edit > Copy and then I'll choose Edit > Paste in Front. So I now have a rectangle that kind of overlaps another rectangle. Let me press Undo. I could color these rectangles different shades of gray. For example, this one will be shaded 30% gray and then this one over here will be shaded around 10% gray. Now, I'll select both of these gray rectangles and I'll set them to Overprint. The result is basically going to be if I create now another rectangle up over here, this is my original red color but I have now created different varieties or different shades of red by simply overprinting different values of black on top of them.
The problem though is that there is no way to create a single swatch inside of Illustrator that contains multiple ink properties. However, let me show you a technique where you can actually simulate this very easily. I'll delete all of my shapes in my artboard. I'll hit Command+A or Ctrl+A to just simply hit at the Delete key. I'll create a brand new rectangle. This particular rectangle now has a fill of the Pantone Red 032, and instead of me actually creating a separate shape, I'm going to go to my Appearance panel, I'm going to choose to add now another fill. So now my artwork has two fills on one single object. I'm going to change the topmost fill to black and I'll actually specify maybe a tint value. So for example, let's do 30% gray.
Now you can easily see that my artwork now has changed to be darker that's because I know that I have a single object that has two fill attributes. I'm actually going to see over here at my Appearance panel that I have Overprint commands applied to both fills. Really, I should only have the Overprint applied to the top though, so I'm going to target the bottom-most fill right here and turn off the overprint for that object. Now, I simply have a single object with an appearance that has two fills, the topmost fill is set to overprint. Now well I can't save this as a swatch, I can save it as a graphic style. So what I'll do over here is simply go ahead, tab with my Graphic Styles panel or even better, I'll show you another little secret that Illustrator has.
I will go back to the Appearance panel. I know that I could always take my thumbnail for my Appearance panel and drag it into the Graphic Styles panel to define a style. But the problem though is that the Graphic Styles panel is hidden right now. Well Illustrator actually has spring loaded panels; a feature that was added now inside of CS4. So if I take my thumbnail and I drag it to the tab where it says Graphic Styles and I hold it there for a second, Illustrator actually brings graphic styles to the front. Now I could drop it in here and I have defined my style. Now that I have created a style, I can draw any new shape inside of Illustrator with one click of a button apply that particular appearance.
Now one final thing to note, it's important to know that right now I have my Overprint Preview turned on. I can see that here in the tab of my document where it says Overprint Preview but if I'm working in just a regular preview mode, I won't be able to see those overprints at all. In reality you can simply go to the View menu, turn your Overprint Preview on and always work inside of Overprint Preview mode. It's a far more accurate display than a regular preview mode. The downside, well, overprint preview requires a lot more processing and therefore redraw may be little bit slower than the regular preview mode. However, if you are working on Prepress, you might want to put up with that to make sure that what you see on your screen is exactly the way that it's going to look like when it prints.
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