Around 300 BCE Euclid speculated on the nature oflight in his work entitled Optics. And for the nexttwo millennia the great thinkers, including Descartes,

Newton, Galileo and Einstein, sought to define it. Today,light is understood to be part of the electromagnetic spec-trum, which includes all frequencies of electromagnetic radia-tion. They are(from high to lowfrequency):gamma ray, X-ray,ultraviolet, light,infrared, terahertz,microwave, radiowave.

The range ofradiation thatframers are con-cerned with is 0 to 2800 nanometers (nm). This includesultraviolet, light, and infrared—radiation that can influencethe fading of artwork over time. Light is the band, or range,of radiation that can be detected by the human eye, approxi-mately 380 to 760 nm.

Frederick William Herschel discovered infrared radiationin 1801 and appropriately called it Heat Rays. Infrared radia-tion causes an increase in the surface temperature of objects.Infrared (meaning “below red”) denotes radiation fromaround 760 to 2500 nm.

In 1802 Johann Wilhelm Ritter looked at the oppositeend of the light spectrum, near the color violet, and called hisfindings Chemical Rays because they were capable of instigat-ing chemical reactions. Violet is the color of the shortestwavelength of light. Ultraviolet (meaning “beyond violet”) isthe term for radiation in the range of 300 to 400 nm.

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Glazing Basics:Protecting ArtBy Paul MacFarland, MCPF, GCF

Why is UV filtering important, how doesinfrared damage art, and can all light causefading?

When reviewing framing industry literature, its com-mon to see the terms visible light, ultraviolet light, andinfrared light. Technically speaking, these terms are notaccurate and can be misleading when considering fine artglazing products. Light is, by definition, the band of radi-ation humans can see; all light is visible. You cannot seeultraviolet or infrared; they are the bands on either sideof the light band and therefore should be termed radia-tion, not light.

There is no precise division in the electromagneticspectrum. Bands diffuse into one another and at some

point share properties. For example, ultraviolet beginsturning to light a little after 380 nm but is generallycharted to 400nm. All three bands of radiation con-tribute to the degradation of art, but not necessarilyequally.

Art obviously needs a well-lit environment, and thelight you see can eventually cause fading in some delicateart media. There is little that can be done about that,although new technologies are beginning to address theissue. The only preventive solution is to limit the amountof time a work is exposed to light, although that’s oftennot possible outside of a museum environment.

However, ultraviolet and infrared radiations, whichyou cannot see, have only negative effects on almost allframed media. Ultraviolet radiation speeds up oxidationin reactive materials as well as accelerating slow fire—the

Radiation from the sun at ground level and from quartz halogen lamps

Radiation from fluorescent lamps

Radiation from incandescent lamps

UVB UVA InfraredLight = what the eye detects

300 400 500 600 700 800Wavelength

(nanometer)

Removed by UV filter

Removed by glass

Ultraviolet

The bands of radiation that concern fine art; adapted from the Canadian Conservation Institute.

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term for paper embrittlement that results from inherentacidic decay. Other effects include rapid paper yellowing,often within a few days, in low-quality, lignin-rich paperlike newsprint as well as the chalking of oil paint withphotosensitive pigments such as zinc white. Other artists’paints also show eventual chalking.

Most wood turns gray under UV, although pale woodsturn yellow. It also assures the weakening and eventualfragmentation of textiles, including wool, silk, cotton,linen, canvas, and cloth-fiber papers. Sensitive color fadingand the disintegration of image media are problems thatare compounded when incorrect temperature and humidi-ty cycling are added to the effects of UV radiation.

A standard measure of fading, the ISO Blue WoolsScale, was developed in the 1920s. It was originallydesigned to test the color permanence of dyes used by thetextile industry. It is now widely used by the printingindustry as a measure the lightfastness of pigments, inks,and dyes.

The standard card has eight strips of blue wool with arating of one to eight, each about two to three times assensitive as the next. One indicates the poorest color fast-ness, and eight is considered lightfast and permanent. Twocolor samples are made for testing. One is kept in the dark

Infrared radiation dropoff with acrylic glazing.

Chart provided by Evonik Industries, manufacturer of Acrylite glazing.

as a control, while the second sample is placed alongside ablue wools test card in the equivalent of direct sunlight fora predetermined time. The fading is then compared to thecontrols and assigned a blue wools number.

Infrared radiation, in contrast to UV, heats the surfaceof objects. Heat promotes the aging process. The higherthe temperature, the faster the deterioration of organicmaterials. Changes in temperature also affect changescaused by humidity, either by increasing it—thus promot-ing mold and other destructive biological activities—orevaporating moisture to the point of desiccation.

For fine art materials like paper and textiles, thedestruction caused by heat basically doubles for every 10°Fover room temperature. Incorrect temperature is therefore

increased level of important thermal protection.

UV Filtering

The percentage of UV filtering by a glazing product is agood place to start when selecting a glass or acrylic. Mostmanufacturers claim a very high level of UV filtration, cit-ing a variety of organizational statistics as evidence of theirproducts’ superiority. While these products all do a goodjob at what they say they do, it is important to note thatthe conditions and materials used to test the glazing prod-ucts are not all the same. Nor are the recommended stan-

second only to the impact of UV radiation in its potentialfor damage, which closely followed by humidity.

UV and Glazing

Most regular window glass filters UV up to about 340nm.To be considered preservation quality, modern glazing(glass or acrylic) must include an effective UV filter.Framing-specific filtered glass and acrylic have been avail-able for more than a quarter century and continue toimprove. The fact is that today, UV filtering glazing is thestandard for all art presentation, with most fine framershaving eliminated standard clear glassyears ago.

Contemporary glazing productsprevent nearly all UV from reachingthe work, although manufacturers con-tinue to talk about who has the biggestpercentage. There may sometimes betradeoffs between clarity and theamount or type of UV filtration, but inthe scheme of things, the differencesare relatively minor.

Glass still dominates the globalmarket as it is well known and trusted.However, acrylic is rapidly gainingmarket share for several important rea-sons. It is lightweight—generally halfthat of its glass equivalent—is up to adozen times more impact resistant, andis available in different thicknesses oflarge and easy-to-handle sheets.

Infrared and Glazing

When discussing the issue of infrared-induced temperature increase, it isimportant to note that glass is a goodthermal conductor and a bad thermalinsulator. Conversely, acrylic is a badthermal conductor and a good thermalinsulator. That means they’re oppositeswhen it comes to transferring theeffects of significant temperaturechanges. Glass passes temperaturechanges outside the frame directly,often resulting in condensation on theinner surface of the glazing. Acrylicslows this transfer, thus providing an

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dards uniform among the various testing agencies. The organizations that have published data on UV fil-

tering include the International Organization forStandardization (ISO), ASTM International, Library ofCongress, FACTS, PPFA, Fine Art Trade Guild, CanadianConservation Institute, and the American Institution forConservation of Historic and Artistic Works. If you haveany questions about individual products and testing, youshould look at the independent organization’s testing pro-cedures. The one thing they all agree on is that the morecontrolled the environment is, the better the filter will per-form.

While UV filtering specifications may vary, it is wor-thy to note that most leading glazing manufacturers rec-ommend taking such steps as reducing overall light levels,installing low UV light sources, and avoiding hangingworks in direct light. These and other factors, such as con-sistently low humidity and controlled room temperature,actually work in conjunction with a good UV filter forpeak performance.

Other Issues

Glass does not generally have a problem with static charge,

but most acrylic glazing products do, especially in lowhumidity. Friable art media such as pastel, charcoal, chalk, orartwork on thin Asian-style papers or lightweight plastics areattracted by static-charged acrylic. For artworks such asthese, filtered glass or static dispersing archival acrylic isrequired.

Airspace created by multiple mats and spacers or combi-nations of the two help dissipate the heat caused by IR.Wide mats also provide an extended bearing surface for glaz-ing. Both glass and acrylic will bow under the right condi-tion—rarely a problem for glass, but not so for acrylic.Acrylic glazing is flexible and therefore subject to deflection,which may cause visual distortion under extreme conditions.The larger the artwork, the thicker the acrylic required andthe wider and deeper the mats need to be.

Along with the development of effective UV filtering,glazing surfaces have significantly improved in recent years.Anti-reflective and anti-static coatings, scratch resistance,anti-abrasive surfaces, improved cleaning ability, and ISO18916 Photographic Activity Test (PAT) approved glazingare available in most international markets.

Other Factors in Choosing Glazing

A framer’s obligation is to exceedclients’ expectations and create thebest product to meet their needs. Thatgoal is the reason for choosing filteredglazing and the other preservationgrade components. However, both theframer and the client have anotherinterest—how best to display the

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work. How a client sees the artwork inthe environment they choose isimportant, not in a theoretical appli-cation but an actual space. There areseveral other factors beyond UV filter-ing that should be considered whenselecting glazing. Among these are:• Clarity – Light has to pass through

the glazing twice before it reachesthe viewer’s eye, once to illuminatethe surface, once to reflect back asthe image a viewer sees. Some art-work demands absolute clarity andreflection-free surfaces. Water white,low-iron glass is often preferred forvery fine detail.

• Optical Distortion – Especiallywhen there is ¼” or more airspacebetween the glazing and object sur-face, distortion can occur with someproducts, especially when largesheets of thin glazing are used.

• Tint – Does the glazing have a tint?Try the printer paper test. Lay asheet of glass over half a sheet ofbright white printer paper. Any tintwill be apparent.

• Orange Peel Effect – How smoothdoes the surface appear, especially atan oblique angle? This can be verydistracting, especially with photog-raphy.

• Deflection potential – Could a sheetof glazing bow, and can you plan forthat possibility? There is not muchproblem with glass, although once itgets beyond 40”x60”, it gets trickyto handle unless it is a laminatedproduct. Bowing can be more of anissue with acrylic. As the sizeincreases, so should the thickness ofthe sheet.

• Ease of Cutting – Can the productbe cut from either side? If not, is thecutting side properly marked on allsheets? Do extra precautions need tobe taken with glazing cutters?

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• Distributor Custom Cutting – Distributors have addedcustom cutting to their services in recent years. Anextremely important service—given the wide variety ofglazing products available—it requires stocking an inven-tory that is now beyond the ability of many framers, asthe storage space alone is prohibitive. Partnering with local

Paul MacFarland, MCPF, GCF, is an inter-nationally recognized master framer andindustry historian with more than 30 years ofhands-on experience. His work is found inpublic and private collections in the Americas,Europe, and East Asia. MacFarland has beenactively training custom framers, collectionpreparators, and art handlers since 1984 and

is the founder of Art Preservation Resources, a consultingand training organization working with fine art preparationprofessionals, businesses, and institutions worldwide. He isthe author of numerous industry articles, procedural manualsand essays, and he lectures on fine art and framing at theNational Conference in Las Vegas.

distributors for accurately cut and inspected preservationglazing products is the only way for many retailers toeffectively offer a wide range of options for discerningclients.

It is the framer's responsibility to limit any detrimentalinfluences in framing whenever possible. Often, this meanskeeping up on the new developments. While glazing hasbeen the subject of contention and commercial speculationfor more than 25 years, the reality is that framers have neverhad such an extensive selection of glazing products to offeras today. They should exploit these resources for the good oftheir businesses as well as that of their clients. ■

An Alternative Approach

Preservation technology continues to inspire innovativesolutions. For centuries collectors and museums useddark curtains to cover very sensitive textiles, coloredprints, and lightly pigmented paintings when not beingviewed. VariGuard SmartGlass is a new electronicallytintable framing technology that works like curtains tolimit an artwork’s exposure to light and UV radiationonly when it is actually being viewed. SmartGlass ismade by laminating a film containing microscopic parti-cles between glass or plastic sheets. When no electricityis applied, the particles are randomly positioned andblock radiation. When electricity is applied, the particlesalign and allow light to pass, and the artwork is properlydisplayed.

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