From the Conservator's Bench: Glazing Paintings
In the conservation lab, we are often asked about glazing paintings. Glazing is the term used for any type of glass or acrylic panel that protects a work of art while it is on display. Why glaze a picture? Glazing acts as a physical barrier against dust and pollutants. Dust can become embedded in paint, making it difficult or impossible to remove without harming the painting. Grime has oily components that stick to paint, paper, and delicate photograph surfaces, and can result in disfiguring stains. Household pollutants, like cooking exhaust and splatters, cigarette smoke and fireplace use can form a yellow film on the surface of a picture.
Glazing keeps fingers and noses off delicate surfaces. Everyone knows that you aren't supposed to touch art, and for good reason. Oil paintings often have brittle surfaces and a little pressure can sometimes dislodge a paint flake. Acrylic paintings can be fairly soft and easily dented by a fingernail. Works on paper get smudged and grimy, and photographic prints will reveal fingerprints after a few months.
Glazing also helps to mitigate light damage. Oil paintings are fairly resistant to normal light damage (the oil medium encapsulates each colored pigment particle, and acts as its own glazing, filtering the light before it reaches the pigment particle). Watercolors, gouache, pastels, colored paper and photographs fade noticeably, and often quickly and unevenly from light exposure. All light damage is cumulative and permanent, so it is important to prevent light damage at all stages.
Ultraviolet (UV) light, is a high-energy component of light that the human eye barely sees, but is extremely damaging to many surfaces. UV light is present in nearly all forms of light, including sunlight and fluorescent light. UV light exposure causes artwork to fade and become brittle. It causes paper and natural fibers to turn yellow-brown.*
There are so many choices for glazing, how do I choose?
Each type of glazing has pros and cons. You need to determine what is right for you. There are two primary types: glass and acrylic. However, each type is also available with options that block UV light, and coatings that change the optical qualities. Discuss the options with a good preservation framer. A framer should carry many types of glazing and be able to show you what your art will look like behind the different options.
All framing materials should be acid-free and lignin-free, and a simple mat should be sufficient as a spacer to ensure that the artwork doesn't touch the glazing when it is framed.
An oil or acrylic painting doesn't require as much UV blocking, but watercolor and gouache paintings should be fully protected. Although UV protective products will slow such deterioration, it is still important to hang valuable art away from direct sources of light.
Do I need to glaze my picture?
Not necessarily.
Only you can make decisions for your art and how you want it to be displayed and cared for in your home. Some people choose to glaze their art so they don't need to worry as much, but other people don't like the way their art looks behind glass. If you choose not to glaze your art, I suggest taking these precautions: Choose a location that doesn't get much light exposure and that is far away from the kitchen and fireplace, and occasionally dust it gently with a supersoft and clean artist's mop brush.
*Energy transfer from UV excitement breaks some chemical bonds and rearranges others, resulting in shorter bond-lengths overall. As visible light is bounced through the shorter chemical bonds, it appears yellowish to the eye.
If you have questions about artistic techniques or preservation, you can ask Victoria Book Lupia, our chief conservator. Send questions to: GMConservation@utulsa.edu.