ConeColor Pro Longevity and Indoor Lighting

This paper is intended to address ConeColor PRO ink longevity when displayed in various indoor lighting conditions.

Background

ConeColor PRO inks have been developed by Vermont PhotoInkjet to imitate the color gamut of the Epson Ultrachrome K3, K3 Vivid and HDR inks when used with the Epson printer driver and Epson recommended color workflow. Normally, third party ink developers attempt to match each individual ink component and hope for good results at the end. Because Epson uses proprietary pigments coupled with high-performance dyes in each of their inks, it is not actually possible to perfectly color match in this traditional manner. Further, the proprietary nature of their pigment/dye hybrids means that there are not correspondingly available pigments on the market with which a formulator can work with. Competing color inks to ConeColor simply do not have good color matches to Epson and require the use of ICC profiles.

Vermont PhotoInkjet took another path to development that centered on the actual color gamut produced by the Epson printer driver. Because Epson produces such an intense and difficult to match ink, its own printer driver has to reduce the actual maximum ink density in order to properly reproduce a traditional RGB image. Vermont PhotoInkjet chose to match the actual gamut of the Epson ink systems as produced by the Epson drivers. As a result of producing such a close color match, a user of ConeColor PRO inks can use the Epson supplied ICC profiles.

Many indoor locations are unsafe for dye inks but are safe for pigment inks

Kodak indicates that 120 Lux is the limit of safe display conditions for dye color photographs and that 90% of all color photographs are displayed in 120 Lux or less. Wilhelm indicates that 450 Lux is the limit of safe display conditions for color pigment photographs. An interior room in a house lit indirectly by incandescent light is considered to be 120 Lux. Museums are limited to 50 Lux (for comparison). Bright offices are about 450 Lux but often much brighter. A print displayed at 450 Lux has only 25% of the longevity it would have if it were displayed at 120 Lux. A print displayed at 5000 Lux would have less than 3% of the longevity it would have had it been displayed at 120 Lux.

A good perspective to keep in mind in comparing dye inks to pigment inks is that it would take years to damage a pigment print displayed in an unsafe condition, whereas the same display condition might deteriorate a dye print in just weeks. Another perspective to keep in mind is that museums display at 50 Lux or lower and although much dimmer than a safe display condition of 120 Lux, it is more than adequate for viewing artwork. Galleries, because they are trying to sell work, almost always display artwork in an unsafe level of illumination. They are terrible examples to follow if you wish to preserve the artwork you purchase from them.

Longevity Testing

How long a print lasts is the subject of much controversy. OEM’s boast significantly high numbers. Most OEM ink and media users believe that their prints will not fade for 100 years if the OEM claims that a specific ink/media combination has a longevity rating of 100 years. However, that is simply not what the OEM is actually reporting. What they are reporting is that at 100 years, the print will have so badly faded to a 35% loss, that anyone can easily detect the fade. The term “easily detected fade” is used to describe the endpoint that the OEMs are using for their fade ratings – and it is an industry standard endpoint.

The industry standard WIR Visually-Weighted Endpoint Criteria Set v3.0 which is used by all the major printer OEM’s to give their longevity ratings does not measure for fade in neutrals, flesh tones, near neutrals, near whites, mixed colors, saturated colors, the paper, etc. What the industry standard tests by Wilhelm do measure are simple densitometric changes in a 1.0 and 0.60 density patch each of cyan, magenta, yellow and three color black. When any one of these patches has faded about 35%, assumptions are made on all other possible colors and a longevity result in years is given for when the print will have faded about 35%.

While a research scientist at Wilhelm Imaging Research (WIR), Mark McCormick-Goodhart (Aardenburg) invented the WIR i-Star, a new test method based on CEILAB colorimetry for evaluating the permanency of photographic images. The WIR i-Star uses a complex color target that is measured with a color spectrophotometer rather than with a densitometer.

The WIR v3.0 standard test target on the left, the WIR i-Star test target on the right.

The WIR i-Star is the most advanced method for evaluating the light stability of inks and making longevity predictions. Some of the other benefits of using WIR i-Star are that fade results for the first time can be compared in prints that use different ICC profiles (yes it makes a difference), or from cartridges that are in different stages of nearing exhaustion (yes it makes a difference), or to determine when the OBAs in a paper will affect the color appearance of an image (yes it makes a difference). Most importantly, the i-Star can be used to determine when fade will first be visible (about 5%), or/and when it has reached 35% fade, or/and many intervals in between.

Unfortunately, the OEMs are still not using WIR i-Star for their current longevity ratings. There is no way to know if that is by choice, request, the expense of performing i-Star, or because an i-Star would reveal fade levels far below the industry standard 35% and upset consumer expectations that have been established. The costs of producing i-Star tests is exceedingly expensive when compared to the current fluorescent bulb v3.0 tests.

IMHO, replacing the current density based CMY testing method and target of WIR v3.0 with the color and luminosity based WIR i-Star target and measurement method but keeping the 35% fade point would be a great interim move by the OEMs. They could then give a fade rating based upon fade that can first be detected (about 5%) by visually trained humans and a second rating based upon when it is easily detected by any human (35%). An OEM longevity rating might be something like 13 – 120 years. It would force more of the responsibility on the consumer to read the actual data. The i-Star is also designed to give varying lengths of longevity in varying display conditions. The consumer looks up their needs within the data and has a clear idea of a display prediction for their display condition. Further, if they bias their needs on portraits, or black & white made with color inks, or very saturated color they will find that some media/ink combinations actually have better or worse results in these areas. It is as near perfect a system as it is complicated. Unfortunately, the measurement of paper white causes a bias against the inks in the lighter shades. While it informs what happens to the OBAs in the paper - it may give a poor impression of the performance of the ink. It is this area which will require more work in the near future. Incidentally, the WIR v3.0 does not measure paper white or near white.

Our experience

Vermont PhotoInkjet began utilizing the Wilhelm Imaging Research WIR i-Star beta several years ago. By using i-Star, we are able to effectively evaluate what changes to individual color positions will do to the overall light stability of an ink set as it relates to the entire color gamut of a print. It actually helped us to develop many of our new stable dye ink sets.

We did not use the i-Star to make longevity predictions based upon the industry standard “easily recognizable fade” of 35%. We believe that 35% fade is not a criteria for professional artists and photographers. Rather we faded samples of both ConeColor PRO and Epson Ultrachrome until both samples had faded at least 5% (where humans first detect fading). We used a late generation Atlas accelerated testing chamber that is filtered to simulate sunlight through window glass. The unit is temperature controlled (stays cool inside while generating tons of heat which we vent outside). The amount of light energy the targets receive is measured and controlled by a computer to compensate for fluctuations due to either electrical load or bulb decay. We use an automated x-Rite DTP70 measuring system. The DeltaE differences are calculated using X-Rite Measure Tool which compares faded targets to targets kept in safe dark storage.

The two following i-Star visual measurement sets are for Epson Ultrachrome and ConeColor PRO.

Criteria

Light Source: Atlas Suntest+ Irradiance of 765 W/M2 which equals 170 KLux or 170,000 Lux *
Filter/Glazing: Simulation of Sunlight through Window Glass
Light Exposure Cycle: 411.6 hours - one period.
Average Illuminance during “on” cycle: 170,000 Lux
Average Temperature: 24 ̇C over full test duration
CIELAB measurements: D50 2 ̇ observer, Xrite Gretag/Macbeth Spectrolino/Spectroscan

We stopped the i*metric test when both of the inks arrived at a deltaE difference of 5 (or a 5% fade). At 70 Megalux the 3 of the 31 Epson ink test patches reached deltaE 5 and all of the test patches averaged 4.0. At 70 Megalux 3 of the ConeColor patches reached deltaE 7.95 and all of the test patches averaged 3.75. 70 Megalux is equivalent to 70 years in a moderately bright home.

Longevity Ratings

Below are ConeColor PRO longevity expectations* in regards to varying levels of illumination (lux) at 12 hours per day from safe display conditions to extremely abusive display conditions:

All of the above are indoor environments. Some inkjet printer operators may consider any of these environments to be the same because they are all indoors. However, the intensity of the light is directly proportional to the amount of fade. Time is the constant. Where 35% fade is the current industry standard endpoint used by all OEMs testing at WIR and indicate "easily recognizable fade", we have tested these "fine art and photographic" inks to a minimum 5% fade which is the amount of fade that is first recognizable. Where a100 year rating from EPSON is for when the ink/media combination will have faded 35%. the above ratings are for when fade is first noticeable.

Actual print stability will vary according to image, display conditions, light intensity, ICC profile, RIP or driver settings, humidity, and atmospheric conditions. Vermont PhotoInkjet, LLC and InkjetMall do not guarantee longevity of prints. Ratings do not estimate the durability of the media or paper itself. For maximum print life, display all prints under glass or properly store them in archival conditions, use uncoated acid-free and lignin-free paper for best practices.