Bleeds and crop marks are crucial components in being able to produce print projects properly (especially when bleeds are necessary).
Bleeds in particular can be an area of frequent misunderstanding for people new to the print world. When a print job ‘bleeds’, it simply means that the ink prints right to the edge of the piece of paper - after it’s printed and trimmed.
To achieve that - the ink printing to the exact edge - we actually need to print ink ‘past’ the edge, so that we can then trim the piece, cutting right through the ink essentially, to finish with a cleanly trimmed, printed edge. The ‘crop marks’ are the tiny little lines that are printed just outside and away from the corners of the final trimmed size of the printed piece. We use those little lines to determine the exact trim lines.
Trimming printed pieces accurately is very important in producing quality print jobs. Please know that due to slight variances in paper sizing and slight movement of the paper and cutting blades, there may be very small differences between pieces within a specific print run. Printing an extra 1/8” (on average) of ink past the planned cut line will more than allow for slight movement during the trimming process, and minimize any unintended white areas along the edge.
Bleeds are set up in the electronic files - they have to be done prior to imaging the printing plates. Very often, when clients setup their files and produce print-ready pdf files, we need to go back into the files and correct the bleed settings. This happens quite a bit, which is why we have graphics staff devoted to ensuring true, print-ready files. We can fix most bleed issues, and sometimes have to be very creative in our approach. For example, if a file has been created with the exact edge of a photo lined up exactly with the intended trim line, we often can’t simply move the photo over 1/8” as that would affect the rest of the printed piece. So sometimes we can enlarge the photo by a small amount and get that 1/8” we need to make sure our client gets the quality they want.
Crop marks must be offset (out and away from the trim lines) by at least as much as the bleeds. So, if you are bleeding your graphics / images 1/8” outside of the trim line, extend your crop marks at least 1/8” away from the edges. If you need more explanation of that, just write.