Color Matching 101
Many variables affect the way a printed color is perceived, and when any one of those variables changes, so does the appearance of the color. With a color measurement device matching become a science . Without a color measurement device color matching is an art.
For a color to exist three things must be present: an object, light to illuminate the object, and an observer (either a person or a color measurement device.) The majority of variables have to do with the object. When looking at the object that you need to print you need to consider the following four factors:
- The object’s base color and surface characteristics (such as gloss and / or texture).
- The number of printing passes required to achieve the desired opacity (single or multiple passes).
- Additives (such as thinner and hardener) used in the ink for production.
- The process used to apply the color to the master sample (could be screen printed, hot stamped, offset printed, spray painted, etc.)
Base Color and Surface Characteristics
An object’s base color has the greatest influence on the appearance of pad printed color, because pad printing deposits a very thin layer of ink when compared to most other processes. When you look at an object what your eyes “see” is the light reflected off of the object the thin layer of ink, not just the ink. As a result, the effects of the object’s color will be more apparent when you look at lighter colors printed on darker objects than the opposite.
Gloss level and/or texture also play an important role. When you view a specific color printed on two different surfaces, you will most likely perceive two different colors entirely. Colors printed on high gloss substrates normally appear brighter or sharper than the same color printed on a dull substrate.This is because the glossy surface reflects more light back to your eyes than the dull surface. Textures have a similar effect because they result in a lot of light reflecting off of the substrate at different angles, making the color appear darker.
The lesson to learn regarding the object is this: The more closely the mastercolor sample represents what you will be printing on (for color, gloss and also texture), the better off you’ll be.
Number of Print Passes
As previously mentioned, when you “see” a pad printed color you are usually seeing the color of the ink and the object. The thickness of the dried ink film is usually about 20% of the cliche etch depth, which is between 0.0002” and.00025”. It is sometimes possible to reduce or eliminate the influence of the object’s base color by printing twice (thus increasing the thickness of the dry ink film. If double printing doesn’t give you the opacity that you require, and you are using photopolymer cliches, you can increase the amount of ink that the cliche holds by switching to a lower line screen count, for example a 100 line / cm or 80 line / cm instead of a normal 120 line /cm. Remember too, that when matching color for someone else using a photopolymer it is important to know which line screen they are using so you can do the same in evaluating your color match versus their master.
Anything added to the ink can also affect its color. Thinners, catalysts and other additives are almost always clear and therefore reduce the inks opacity. When you’re preparing a color match for printing to verify its appearance versus the master you should make sure to use the same additives, at the same ratios, as will be used in production.
Color Master Process
Lastly, consider the process used to generate the color master. Here again, the concern is the pad printing limitation of ink film thickness versus other processes. Every process deposits a different thickness, so whether your color master was screen printed, offset printed or even hot stamped you’ll need to adjust your expectations as the accuracy of your color match accordingly. This is especially true when color masters are molded, spray painted or powder coated, because achieving the same level of saturation (or color purity) with pad printing will be difficult
The viewing environment also plays a part in color appearance. When color matching, it is best to evaluate your color versus the master under the same lighting conditions as whomever has the final say as to whether the color passes or fails. If you do a lot of color matching, consider using a light booth with different light sources. If you’ve got a color measurement device such as a spectrophotometer to use as a tool in achieving color matches you’re lucky, since the proper use of such a device removes subjectivity from the process. As long as you and your customer remember that a spectrophotometer is a tool for achieving a color match, and not a tool for final evaluation (pass or fail based on the device instead of the human eye) you’ll be fine.
Color matching is made significantly easier by ensuring that you have a good master sample to work with; preferably one that has the same base color and texture as the object you’re matching color onto. When identifying how deep a cliche, what line screen , how many print passes, which additives and what mixing ratios to use in creating your sample alway sbe careful to make your sampling process as close as possible to the production process.
For more about inks and ink drying/curing check out this video featuring John Kaverman