When you make bread, one of the first steps is proofing the yeast. You do this to ensure the yeast is active (or living) and thus will enable the bread to rise. If the yeast is dead, your bread will not rise and the finished product will resemble a rock. To proof yeast you dissolve in warm water (not too hot as yeast dies at 140 degrees), mix with a pinch of sugar and wait a few minutes for the yeast to foam up. If the mixture is foamy, you know your yeast is active and ready to be used. However, if after 5-10 minutes nothing happens, then your yeast is probably a dud.
There are no guarantees with yeast, and you must proof to ensure everything is going to turn out right. The same holds true in printing. When submitting artwork to a printer, they will proof your files to ensure everything is going to print like your intended design. When receiving the proof, it is then YOUR responsibility to make sure everything looks right. I don’t mean to be harsh by putting the blame solely on you if something is wrong with the proof and you don’t catch the mistake, but the reality is that many printers view a signed off proof the same as a contract. Hence the commonly used term “contract proof” that specifies that you think everything is okay to print. Hopefully you have a true partnership with your printer, where they will also look for issues with files and proofs to ensure all is okay. However, not giving a proof the respect it deserves can seriously cost you some big time bucks.
Why do I stress the importance of a proof, or better yet what can go wrong with a proof? Just ask any printer and they can give you a laundry list of potential issues. For example, your document may have missing fonts and images or low-resolution images. Text may not flow properly causing layout issues (Google “prepress reflow”). The color might not look the same as it does on your monitor. Images on the edge of the trim may be missing bleed (additional image needed to ensure the image runs off the edge of the sheet if small printing, binding and trimming variations occur). If you are uncertain of everything you should look for when deciding whether to approve or not, ask your print sales rep, their prepress manager or search the web.
Why do things go wrong with a proof when there was nothing wrong with the files sent to the printer? To put it simply, the printer changes your file. They have to put it in a format that their equipment can read. When this change occurs, ironically known as RIP, formatting related issues can cause unexpected changes (especially with un-preferred file formats). The printer does this because files come in so many different formats and platforms but the plate processors or digital presses can only read the file in one common language. You can save yourself some pain by finding out what types of files the printer prefers to work with and then design your files in those formats. However, even if you design your document in a preferred format, issues can still occur.
In the new age of printing, where every print project started today needed to ship yesterday, it is certainly easy to quickly scan through a proof to get the project into production right away. Working with multiple customers though, I have personally seen and dealt with the pain of what happens when errors are not caught in the proofing process. A circle of blame ensues where the result is everyone loses.