What is overprinting?
Overprinting refers to the process of printing one colour on top of another, without the latter being covered and without holes being made on the background
e.g. black letters on orange background. The black colour is printed over the orange background.
When and why should we use it?
Indesign and Xpress are setup by default to overprint the black colour. But what does that mean? Offset printers print four colours, one on top of the other. The orange colour is created through the printing of a raster of magenta and then one of yellow. As we all know, black is the combination of all colours, which it can cover and by which it cannot be altered. Designing programs set up black to be printed over other colours by default, so that it won’t mess with the background nor pierce it. This property makes black the perfect colour for printing small letters, because cases of register can be avoided. The rest of the colours cannot be printed over because they will be altered.
However, there is also an exception in the case of the black colour, which we should be aware of.
Black as an ink of the four-colour printing palette is a little transparent, so that it can be mixed with the rest of the inks and create all colour tints. So when placing a black bar on top of a picture, it becomes transparent and lets the pattern of the picture show, as you can see below.
In order to prevent that from happening, we should simply make sure that the background ends exactly where the picture is placed or use a richer colour instead of black (like C30, M30, Y30, B100), so that it’s not printed over.
We also use the overprinting method when we’re designing something that will be cut, like a folder a box etc.
We place the cutter on top of our file, we use a spot colour that does not affect the four-colour and print it over. This way, it is printed as a fifth colour and does not leave a white trace on our background. This not only helps us with designing, but it also helps the printers know exactly what they need to print.
We can use the overprinting method on Illustrator and Indesign through the attributes palette and in Xpress through the trap information window.
As you can see on the pictures, as soon as I deactivate the cutting option from the output preview, my file remains unaltered. The colour is set to be printed over so it does not pierce the background.
Once again, we can this way check the final product we’ll send to the printers through Acrobat. On a previous post you can see what exactly you should check and how you can do it.
Attention!
I have repeatedly noticed the following mistake: Logos that used to be black (and someone had correctly set up to be printed over) being changed to white or other colour without the overprinting option being deactivated, which of course makes the logo disappear when printed on dark backgrounds. When we want to use black logos we should first check whether they’re set up to be printed over before we change their colour.
Overprinting: When and where should it be used? When does it cause problems?