Lightfastness
Also known as: Fade rating · Lightfastness rating · Wilhelm rating
How resistant a print's inks are to fading under light exposure. Independently tested by Wilhelm Imaging Research; fine-art pigment prints typically rate 100+ years under glass.
Lightfastness measures how long a print's colours hold up under display before fading becomes visible. The standard test is run by Wilhelm Imaging Research, an independent US lab that exposes ink-on-paper samples to a controlled light source representative of typical indoor display conditions, then projects forward to estimate the number of years before noticeable colour shift. The number quoted alongside a fine-art print — "100+ years under glass", "200 years under museum glass" — is the Wilhelm estimate.
Two variables drive the rating. The ink — pigment inks, where the colourant is a physical particle, are vastly more lightfast than dye inks, where the colourant is dissolved. The paper — acid-free α-cellulose or cotton rag holds inks more stably than acidic wood-pulp paper, which itself shifts colour over time and accelerates ink degradation.
Display conditions matter too. The Wilhelm rating assumes glazing in front of the print (which filters some UV) and indirect daylight rather than full sun. Direct sun behind regular glass shortens the practical lifespan to a fraction of the rated figure. UV-filtering acrylic restores most of the protection and is the default glazing on our framed orders.
Three things the rating doesn't tell you. Storage longevity — Wilhelm tests assume display, not long-term dark storage where prints last almost indefinitely. Ozone resistance — separate issue, affecting prints displayed unframed in heavily-polluted urban interiors. Paper longevity — a print may have lightfast inks but lose its paper substrate to lignin acidification within decades; archival paper closes that gap.
Every Clark & Darcey print is made on Hahnemühle German Etching 310gsm with archival pigment inks, both Wilhelm-tested for a combined 100+ year rating under glass. Combined with UV-filtering acrylic and a stable indoor environment, the practical longevity is generational.
Common questions about lightfastness
- How long will an archival print last without fading?
- Fine-art pigment prints on archival paper are Wilhelm-rated for 100+ years under glass — the standard fade-rating benchmark from independent lab Wilhelm Imaging Research. The number assumes glazing in front of the print and indirect daylight; direct sun behind plain glass shortens the practical lifespan considerably, while UV-filtering acrylic restores most of the protection.
- What is the Wilhelm fade rating?
- The lightfastness rating produced by Wilhelm Imaging Research, the standard third-party testing lab for archival prints. They expose ink-on-paper samples to controlled light at a known intensity, then project forward to estimate years-to-visible-fade. Most fine-art pigment-ink-on-archival-paper combinations rate 100+ years under glass; the very best combinations rate 200+ years.
- Will my print fade if I hang it in a sunny room?
- All prints fade faster in direct sunlight than they do in indirect daylight, even archival ones. The 100-year rating assumes typical indoor display, not a south-facing window. For sunny rooms, fit UV-filtering acrylic on the frame (we use it by default), avoid walls that catch direct afternoon light, and rotate the piece occasionally so light exposure is even across the surface.