Improper framing can make your print look yellow and faded if you are using inkjet paper that contains Optical Brightener Agents (OBAs). The latest, brightest white inkjet papers such as Epson’s Exhibition Fiber paper use OBAs. Optical Brighteners are additives used to make paper look whiter. They may also be called artificial whiteners. These brightener agents take in ultraviolet (UV) radiation and re-emit it in the blue spectrum, which is visible to our eyes. UV radiation is one of the main contributors to prints fading and discoloring over time, so if you are framing for preservation, you want to use glass with a UV filter. Guess what happens if you block UV radiation on a paper with optical brighteners? The print will instantly look yellow and faded since the OBAs have no UV radiation to transform.
Most inkjet papers have optical brighteners except for those marketed with something called “natural white”. Find out more about how they are used in paper here.
OBAs are one of the main reasons for the slight warming effect that occurs when you place glass or acrylic with a 99% UV filter over a print. If you cover a piece of Epson Exhibition Fiber paper, which contains high levels of OBAs, with UV filter glass and view it in daylight the warming effect will be exaggerated with an obvious color shift.
Not only are OBAs neutralized by conservation framing with UV-filtered glazing, they are dye-based instead of pigment-based, which means they are more prone to fading over time. OBAs also impact other colors on the print, so this combined with UV glazing and the normal fading of OBAs over the long term will cause even more color shifts in the print. Aardenburg Imaging Archives has more details on OBAs and print longevity here.
Test: What glazing discolors paper containing high levels of OBAs the least?
For this test, I placed 8 different types of glazing (glass and acrylic) on a sheet of Epson Exhibition paper containing some of the highest levels of OBAs, and photographed them in bright midday sunlight.
Glass or acrylic with a 98% or greater UV filter has the most discoloration. Glass and acrylic without a UV filter will still block 40-60% of the UV light. Reflections and iron in the glass will also discolor or reduce brightness.
Artglass WW AR offers the brightest image, but there is more going on here than just the UV filter. WW stands for water white; it has reduced iron content which decreases the normal color shift and diming that regular glass causes. It is also anti-reflective (AR), meaning more of the light is passing through the glass to the image instead of being bounced away, resulting in the paper being brighter.
The Artglass UV/WW/AR is the same glass with the addition of a UV filter; however, it only blocks 90% of the UV spectrum. This is why it is brighter than the Museum Glass.
Artglass Preservation clear also has a 90% UV filter, but it is not water white or anti-reflective making it the least brightest of the ArtGlass products.
Regular glass does not block significant amounts of UV radiation; however, its iron content causes a blue green filtering effect reducing brightness more than standard acrylic.
Standard acrylic is optically pure, but has more natural UV blocking capability than regular glass. It also has more reflections than AR glass. My guess is reflections are the primary cause of regular acrylic not being as bright as anti-reflective glass with no UV filtering.
The Tru Vue conservation clear glass is not bright at all due to a 99% UV filter and no anti-reflective coating. It is also not water white. The Tru Vue Museum glass demonstrates the strongest evidence of how UV-filters impact papers with high levels of optical brighteners because Museum glass is optically pure and anti-reflective. Still, the warm color cast over the print is obvious, just like it is with the Acrylite OP3. Although OP3 acrylic is also optically pure, it is not anti-reflective like the Museum glass.
If you are concerned about print longevity, avoid using inkjet papers with optical brighteners. If you are mostly concerned with bright whites then frame without any glazing or use a glazing that is optically pure and has no additional UV filter such as regular acrylic or water white glass.