Glass with ultraviolet protection keeps blue pigments from fading.
Frame glass protects watercolor paintings from dust, airborne pollution, humidity and ultraviolet (UV) light, all of which damage the paper, fade colors and ruin the art. Glass protects the paper but is heavy while scratches in lighter weight Plexiglas can ruin the view of a picture. "Any work of art on paper should be protected with some kind of glazing," says framing expert Meg Nicks, which means framing it behind some kind of glass or Plexiglas.
Glass
Picture glass is thinner than window glass to create less distortion but reflects images that obscure parts of the picture. Non-glare glass is pitted in an acid dye to reduce reflections but allows color-bleaching ultraviolet rays through that fade the colors. For valuable paintings, non-glare glass that blocks UV rays provides the best protection.
Framing
Watercolor pictures are painted on paper of different weights. The lighter the paper, the more it will buckle when water and paint are applied. Framing it between glass, a mat and a rigid backing keeps the paper as flat as possible, but it should never be in direct contact with the glass. Glass can scratch the paper as it expands and contracts with humidity levels. Use pieces of plastic called spacers or a second frame of mat board (a "mat") to create a 1/4-inch space between the paper and glass. Made from 4- or 8-ply mat board, mats come in colors to enhance the artwork.
Frames
Factory frames use thin mat board, which is not thick enough to keep lightweight watercolor paper separated from the frame glass. Mass-produced frames have loose fasteners on the back that allow dust inside that can mar the painting. Factory-produced double glass ("floating") frames need to provide space between paper and glass or shouldn't be used for watercolors unless they are made of porous Plexiglas.For valuable or treasured watercolor paintings, Nicks recommends using UV-blocking glass, 3/16-inch spacers or 4-ply mats, brads to seal the picture snugly between the glass and backing and a paper dust cover glued securely to the frame back.
Cost
Watercolor pictures need glass for protection from the elements.
Plain clear picture glass is the least expensive and provides some protection from UV rays while non-glare or anti-reflection (AR) glass doesn't prevent them from fading paint colors. UV-blocking glass costs more but protects the colors. Top-quality AR glass coated with UV protection like a camera lens costs hundreds of dollars. It filters out harmful ultraviolet light and minimizes reflections and glare without tinting the painting or distorting it with imperfections in the glass. "People will touch it because it doesn't look like there's any glass there," she said.
