Markings on printed food packaging

I recently noticed that if you look on the bottom seam of most potato chip and other snack food bags there is a series of colored dots.
And every bag is different. I am currently looking at 3 different bags. One has 8 dots on the left side of the seam and they seem to be full and half tones of 4 different colors. Bag two has 6 dots on the left side of the seam (those appear to be full and half tones of 3 different colors and 7 dots on the right side of the seam ( those appear to be seven different colors although some are much lighter than others). Bag three has 7 dots on the left side and 8 on the right side, and all appear to be different colors.

So what are these dots and why so many unique configurations? I’m guessing this has something to do with the printing process but what, exactly? And what determines how many dots and what color dots a bag gets?

I also noticed that boxes have similar markings but usually rectangles, not dots. And I did find a couple of bags with no dots at all -why do some bags not need them?

Are they registration marks?
I could guess at your answer, but ‘registration marks’ is the term you need. If you google that, I’m sure you’ll be able to find more information that you could ever want.

Was in the print industry for 25 years, although in commercial print, not flexible packaging.

Those are either registration marks or color bars.

Registration marks are usually some type of crosses or other alignment type targets, however there are some systems that do use dots. In simple terms, all the systems utilize some method to visually measure the distance between the various color marks, then send data back to the press control systems that moves the out of register color relative to the other colors both side to side and forward or back.

Color bars are used to “measure” the color in color space to determine that it is correct. This is done using what I think I remember was called a spectrophotometer. Color bars are also used to measure ink density. In flexible packaging (chip bags and the like) the product is printed roll to roll so some sort of visual camera type system might be used to measure color. I’m not as well versed in these printing processes, so I don’t know how much control of color density there is compared to the offset printing process.

I had always thought it was just a color print registration test bar, that a human being in quality control could glance at quickly, and know if the printing process was out of alignment. A worker in quality control would not notice if something in a busy multi-color package print was printing wrong, but could just glance at a feed of packaging and see of the dots were misaligned.

Quality control is probably rarely done by humans anymore, being replaced by digital readers, but I presume that is where it got its origin.

yeah the boxes are fixed , but the colours in use vary
*some of them, with the design. It might even be software generated.

You know, the food packaging laws require certain information be present on the package. It could be there to have quality control detect the absence of a required dye/ink easier.
Missing info could even result in a recall

  • other boxes, just whatever the operator was using last time he decided that there was some sort of issue with colours. The tubs of dyes are meant to be standard, but if there is variation in one dye , he might adjust the colours in a number of the boxes to help understand the variation… then just leave them until the next problem requires a new set of colours to diagnose.