The real-world atmosphere contains mixed gases that cause color fading. Ozone (O3), nitrogen oxide (NOx) and sulfur oxide (SOx) must all be considered, therefore, as factors that effect image permanence.
Gas fastness has been improved with the combination of new genuine Canon dye inks, the 2008 new FINE print heads and "Photo Paper Plus Glossy II PP-201", "Photo Paper Pro II PR-201" or "Photo Paper Pro Platinum PT-101". It achieved "gas fastness approx. 20 years" which is longer than previous "gas fastness approx. 10 years".*
 
*About gas fastness:
Criteria for estimation
Estimated gas fastness is made under the following test conditions: Temperature (24°C) and humidity (60% RH) are controlled in an environment of mixed gases of O3, NOx and SOx. The ratio of the gases is typical to indoor air composition (O3: NOx: SOx = 3:19:1) with 100 times concentration in order to accelerate color fading.
 
Criteria for estimation of print longevity shown above
Estimates for image permanence are made using the Wilhelm Imaging Research, Inc. endpoint criteria “WIR Visually-Weighted Endpoint Criteria Set v3.0” as follows; Samples are printed with an optical density of 1.0 and 0.6 (each black, cyan, magenta, yellow) by default printer driver setting of each media. The point where monochromatic/reflective optical density shows loss of 20-35% (figure set respectively for each color, starting density of 1.0 and 0.6). The point where the difference in color balance of yellow, magenta, and cyan (each component in composite black) reaches 12-18%.