Reflective surfaces and metallic inks are very popular for printing and packaging applications. Consumers love the look; but for printers, these substrates and inks are expensive and make color control a challenge.
Today we’re taking a look at the measurement options available for controlling these very marketable print and packaging applications to help printers and converters meet brand owner expectations and maintain the highest possible quality output.
Sphere vs. 45°:0° - What’s the Difference?
There are two primary types of spectrophotometers used in the printing and packaging industries today – the traditional 45°:0° (or 0°:45°), and the spherical (aka diffuse:8°).
With a 45°:0° spectrophotometer, the first number refers to the angle of illumination and the second to the viewing angle. The light source shines at 45-degrees from the surface of the sample being measured, and the detector receives reflected light at 0-degrees, perpendicular to the object’s surface.
The X-Rite eXact is our most popular 45°:0° spectrophotometer, enabling printers and packaging converters to truly understand, control, manage, and communicate color across the entire color supply chain.
A sphere spectrophotometer, on the other hand, illuminates the object diffusely from all directions, and the detector receives the reflected light at an 8-degree angle from the object’s surface. Spherical in shape, these instruments are lined with a highly reflective, very low gloss, white matte surface. As the light beam strikes the surface of the sphere, more than 99% of the light is reflected and scattered randomly in all directions.
The Ci64, our most precise handheld sphere spectrophotometer, is available in three models with simultaneous SPIN/SPEX, correlated gloss and a UV option. These diagrams show the difference in measurement geometry between 45°:0° and sphere spectrophotometers.
When to Use Each
A 45°:0° spectrophotometer, like the X-Rite eXact, not only considers color, but also gloss and texture. This type of spectrophotometer has been historically popular for measuring color on smooth or matte surfaces in printing and packaging operations, but may not be the first choice for all applications.
One such application is the use of mirror-like metallic reflective surfaces. When printing non-opaque inks directly on surfaces like metallized films, cans, or foil labels, colors will measure as much darker than they appear to the eye. This happens because most of the light that is projected onto the mirror-like surface at a 45-degree angle reflects at the opposite 45-degree angle and is not captured by the instrument’s optics. Since very little of the light is actually captured by the optics, the resulting data indicates the sample is darker than it actually is.
Another scenario that is challenging for a 45°:0° spectrophotometer is a deeply textured material, such as printing directly on foam or plastic packaging materials. In these cases, much of the light will get “trapped” in the deep recesses of the texture, and the shadows are measured as darker than we visually perceive the color. The texture will also lead to inconsistent measurements, which can be demonstrated by measuring the sample at different angles at the same location.
Unlike a 45:0 instrument, where the light is projected from one angle, in the sphere spectrophotometer, the light is reflected and diffused off of the inside surface of a sphere, from nearly infinite angles, before striking the sample area. Most print and packaging users choose to include the gloss component (specular included or SPIN) in their measurement. This collects all of the light that the 45:0 instrument misses. They may also choose to capture the color excluding the gloss component (specular excluded or SPEX), so that other metrics can be calculated. Two examples are the Corelated Gloss Metric, and the Metallic Brilliance Ratio. Check out our SPIN vs. SPEX blog to learn more.
The way that the sphere spectrophotometer illuminates highly reflective metallic surfaces with a diffuse light source provides measurements that correlate with the way the human eye would see the color when looking at the printed image on an aluminum can, metal bottle cap or metallized package. It also illuminates the recessed areas of textured surfaces to provide an accurate and repeatable measurement of foam and textured printed packaging.
What About Metallic Inks?
Metallic inks come in a variety of types and are composed of various kinds of metal flake materials. In most cases a 45°:0° spectro will be adequate for these applications, and a sphere spectro is usually not required for measuring metallic inks. This is because the light that is reflecting off of the metallic ink is more diffused than that from a mirror-like metal surface. So, the optics of the 45°:0° instrument is able to capture more if the reflected light. Only if the ink/coating has a mirror like appearance, would it require a sphere instrument.
So… Which Instrument Should You Choose?
You will be challenged to accurately produce brand and other colors if you don’t have the right instrument.
- If you’re seeing an increased demand to print products with translucent inks on foil or other mirror-like surfaces, or working with highly textured surfaces, asphere spectrophotometer from the Ci60 Series is probably the best choice.
- For jobs that don’t print on highly textured or metallic surfaces, or if you put a white ink over the metallic surface under the color inks, a 45°:0° like the X-Rite eXact is the best option for your needs.
- If you are printing metallic inks, in most cases the eXact will work fine, unless the ink has a mirror-like appearance.
To determine the best instruments for your applications, you must analyze job mix and customer requirements to determine if your critical measurements can be made with one type or the other, or whether it makes more sense to have both instruments available in your facility.
Still Not Sure?
Our experienced Color Experts are available to help you determine the best solution for your workflow.
If you’ve established a good workflow for your paper-based products, but metallized substrates are throwing you for a loop, check out our Effective Color Control on Metallized Substrates blog for help.