Museum Glass and Optical Brighteners
Part of taking control of your digital images is recognizing what the nature of the media is you are printing on and how it affects your presentation. Optical Brighteners, also known as OBA's, are a hot button topic amongst digital printing professionals. Some people will not use papers containing optical brighteners as they don't deem papers that contain them "museum or gallery quality." Optical Brighteners have a life to them, and over time will stop brightening, reducing the paper you are using to its natural base color which is not bright white. Others say that optical brighteners aren't necessarily a bad thing and that all images fade and change over time… so the focus on OBA's is irrelevant. The real issue has more to do with controlling what your audience sees and how lighting and final presentation affects the vision you had for your image.
A typical scenario seen over and over again is that of a photographic artist who does all the proper color management procedures, or works with a lab to specify a paper that reflects their vision (which happens to be a paper with a very high bright white point) and then wonders why their images look different under gallery lighting or when framed with Museum Glass. As our inkjet printers don't contain white ink, the best we can do to establish a white point in our prints is to choose a paper that reflects that vision. OBA's are chemical agents used to create a blue/white reflection off of the paper base when exposed to UV light. Cotton, alpha-cellulose and other paper pulp materials are not naturally bright white, hence additional processes are used to make them white. If you choose to light your print under 5000K, tungsten, LED, fluorescent, halogen or any other type of lighting, prints with OBA's will reflect light differently under these various types of lighting than papers containing no OBA's. The shift can be from yellow to green to magenta depending on the lighting. This phenomenon is called metamerism. More importantly if you choose to use frames containing expensive Museum Glass, you will be blocking the much needed UV wavelength of light needed by the optical brightening agents to maintain the bright white of the paper base you intended. Museum Glass has a UV protective coating which effectively blocks UV wavelengths from reaching your print thus reducing the white point to the natural “off-white” base color of the paper, changing the overall color of your print dramatically. It is great for protecting your prints from damaging UV radiation but at the same time it will dull down your print and cause it to look very yellow…which is something you might not have intended.