IMAGE: Accurate Full Color Image Aging
Tim Quinn and Bruce Ridge, Nazdar
The primary print specifications for color printing have been designed around offset lithography printing on paper substrates (Reference Print Conditions, Pantone, ANSI). This is considered non-durable printing. Durable printing applications have been part of industrial print applications for years with end uses in the automotive, fleet marking, and signage segments of printing.
The Ink Jet process allows printers to print on an unlimited range of substrates which includes many durable substrates. These applications have exterior durability expectations based on the ink / substrate combinations. These expectations have been established through years of real- and accelerated-time weather testing of ink and substrates.
Durable graphics printers should be aware that there is not a standard testing method or practice that takes into account the entire process color image when reporting the weathering data of a durable graphic. Most durable graphics have exterior ratings of one to ten years depending upon the media and ink components used in the graphics’ construction. Until now, these components have been weathered using the single solid color method. There is a new full color weathering process that will create an accurate full color representation of how each of the four colors (CMYK) will change throughout the entire tonal range. This is an introduction to the IMAGE process which creates an accurate rendition of a weathered full color image. The result is visual and has many benefits to durable graphic producers and buyers.
The Screen and Ink Jet processes are the primary printing methods used to create durable graphics. This is attributed to the thicker ink deposit and the versatility to print on highly durable medias. Printing on durable medias with durable inks has been the hallmark of screen printing almost since its commercial inception.
In the durable signage industry, plastics, paints and inks were developed with exterior durability in mind. Eventually these products acquired exterior durability ratings. In the case of the screen-printing industry, the common expectation for most inks and medias is to last outdoors for two to three years, with some products being designed to last up to ten years. Most of this printing has been done with spot colors. As ink jet printing becomes the most popular versatile printing process, it is being assumed that ink jet maintains the same exterior durability as screen printing because it prints on many of the same substrates. Printing on similar medias is only part of the story. The greater ink deposit achievable in screen printing is partly responsible for the durability characteristic.
Real Time Weathering
When it comes to printing exterior graphics, customers want to know how long they can expect their graphics to last outdoors without fading to the point where their message loses its impact. It is common for media and ink to have a durability rating. A printer can then match up the expected durability of a product with their customer’s expectations. The longer lasting the products, usually the higher the cost. Some product constructions may even be built around a written warranty.
As durable product manufacturers send their products to different parts of the world, it is becoming more important to consider the weathering conditions where the products will be used, and not where they were manufactured. Weathering data can now be referred to in weathering zones. The closer you get to the equator, the more intense the Sun’s damaging UV rays become. This map of UV intensity would equate to weathering zones.
The weathering of products has become a precise business in an unprecise world where the weather constantly changes. There are companies like Atlas and Q-Lab that provide weathering products and services. These two specific companies are based in the USA and have weathering farms all around the world in different weathering zones. These zones will include high UV arid and high UV humid zones. Ink and media companies will contract these companies to do controlled real time weathering of their products. Once the samples have been exposed to the outside elements, they will be analyzed to determine what the best combination of raw materials is to make the most durable inks and media. These services are used by all kinds of manufacturers in automotive, fencing, roofing, house paint, signage, and graphic products.
Real time weathering is the best and most accurate, but it takes years to complete. As product development cycles becomes shorter and shorter, real time weathering can become unrealistic in the development stages. Accelerated weathering machines were developed in the early 20th Century, but did not come into common use by printers until the 1970’s. The early machines focused on automotive applications that were being improved to make a car last longer, and look better over time. Once this became verified to correlate with real time weathering, the practice of accelerated weathering became accepted as common practice in product development and testing.
Accelerated weathering is a standard practice for most manufacturers of durable products.
There are ASTM standard weathering cycles or protocols that dictate how accelerated weathering machines should be set up with the hours of light, moisture, heat, and cool down phases to represent specific outdoor conditions associated with certain geographical areas.
It is accepted that the thicker the ink deposit, the better the integrity and durability of the ink layer. Adding an overprint clear to the ink layer will extend the exterior durability one to three years. A laminate will increase the durability even more.
Color Weathering Data
Sometimes these samples are compared visually and sometimes they are measured. The most common measurements made on these samples are:
- Gloss which is measured with a gloss meter. A reduction in gloss is usually the first sign of degradation of a coating.
- Color which is measured with a spectrophotometer. This is usually measured in L*a*b* color. The before and after measurements are calculated using one of the four common color tolerancing formulas.
- Color density is measured with a densitometer. This is measured only on transparent process colors, whites, and blacks.
As a result, if these samples are not just visually compared, but also measured and calculated down to a simple number difference using a color delta formula. The chart below are real measurements taken from three different sets of process color inks being weathered. All measurements were taken on a 100% patch of CMYK (O orange) over an accelerated 36 – month period. All colors do not fade or weather the same. In the end, you are left with a number to represent a color difference.
Color Weathering of Process Color Images
The weathering of inks has always been done with a solid 100% coverage of a spot color. This practice has continued with process colors as most printing today is full color CMYK printing, but this is not accurate for full color images because it is not common for full color images to have solid 100% areas of coverage of C, M, or Y. Testing indicates that when we weather a tonal ramp with the different dot percentages of C, M, Y, or K, the lighter tones will fade much faster than the solid areas. Most full color images have a near infinite number of colors trapping each other in varying degrees. We know that the Magenta and Yellow inks degrade much faster than the Cyan and Black inks. All this combined means that traditional solid color weathering is not applicable to process color images.
IMAGE: Accurate Image Aging
The IMAGE process has taken years to prove accurate as the work was done with both real time and accelerated weathering samples. We have used our color management experience to generate accurate IMAGE profiles. Instead of weathering solid patches of color, we weather the full tonal range of CMYK color in order to create a full color, full tonal range rendering of how color will degrade in all colors, at all different tonal and color build ranges for a particular ink and substrate construction.
Full color weathering data is now real and most importantly, visual. The IMAGE process is created by applying weathering profiles that have been created from actual weathering data showing one-year increments of weathering for an ink and media construction.
In the art department, a designer can apply an IMAGE profile to images in the design stages in order to make the best choice of colors in backgrounds, skin tones, foods, and product placement that will have the longest lasting acceptable color. Accurate IMAGE proofs can be generated prior to approving a job for sales presentations. This can help the sales group to visually sell more durable constructions, or maybe sometimes less durable ones when costs are the primary focus. IMAGE profiles allow a printer to replace a damaged panel on an older installation with consistency. IMAGE profiles show us the future of today’s images.