This is the 2nd blog in this series. If you would like to read the first one click here 4 Keys to Consistent Color – Series Intro
When it comes to printing consistent color there are two pieces of hardware that matter most:
- A Consistent Printer
- A Measuring Device
There is no such thing as a consistent printer! Printer variance is inevitable. One that varies very little over a week is much better than one that prints one way at 8am and quite differently at 5pm. The key is to monitor your printer’s consistency over time to both understand how variable it is and to know when to take corrective action if it varies too much. Variations can be minimized by setting up a process control program whereby you regularly measure the printer’s performance. Additionally, process control software allows you to track any variation and take corrective action should the printer’s performance go outside defined tolerances.
Determine Your Printer Variability:
First, you need to determine the variability of your printing device over a week by taking measurements using a control strip on at least a daily basis and plotting the results on a graph. If the device varies quite a bit over this short period of time, do some digging to determine what is causing the variation. It could be due to a mechanical issue with the printer that is either a maintenance issue or a repair issue. It could be due to environmental changes of temperature and/or humidity. Bottom line, you need to find the reason(s) for the variation and determine if you either want to live with the variation of fix the causes.
If it is found that temperature and/or humidity are the culprits, you will need to decide if adding or augmenting a climate control system is something you are willing to spend the money on. If cost is prohibitive to stabilize the environment, frequent measurement with ongoing tweaks will be the only way to improve print variability.
The second piece of hardware is a measurement device that can consistently take measurements with a high degree of accuracy. When you are reading profiling charts with many patches an automated device makes measurements easy and much more accurate. When it comes to measuring control strips on a regular basis, a good hand-held device is quick and easy. A hand-held device is satisfactory for this purpose since the number of patches on most common control strips is 84 or less.
When purchasing a measuring device for both quality control and calibration, it is important to consider the size of the measurement aperture and its relationship to the graininess of the chart being measured.
High screen ruling offset printing, aqueous inkjet printing and digital printing, if printed on smooth substrates, have a very uniform laydown of ink and don’t require more than a 2 to 3mm aperture.
Coarse screen ruling printing like printing on newsprint or silkscreen printing require a much larger aperture due to the coarse nature of the ink laydown and the often rough surface of the substrates. Large and grand format inkjet printing also falls into this category as the droplet sizes of these printers are quite coarse, requiring a larger aperture. To ensure accurate measurements of these coarse printing processes, an aperture of at least 6mm is required to measure a larger area of each patch in the control strip or calibration target. Taking in more of each patch allows the instrument to average a larger sampling resulting in better accuracy.