Picture framing glass ("glass", "glass conservation", "museum quality glass") usually refers to flat glass or acrylic ("plexi") used to frame artwork and to present art objects in screen box (also, "conservation framing").
Video Picture framing glass
Destination
The main purpose of glazing in the art of framing is to physically protect the artwork from destructive factors such as moisture, heat, and defilements. Glass laminates and some acrylic can be used to protect against physical damage from broken glass and offer protection from malicious attacks. Regular glass and some surface glass treatments can also filter out some of the damaging ultra-violet (UV) and heat (NIR) radiation. Artwork requiring protective glazing is provided on paper or cloth (including photographs), which contain pigments and dyes that absorb UV and are susceptible to discoloration. In the case of framed objects or UV resistant artwork, UV protection can still serve the purpose of maintaining the integrity and color of non-conservation class framing materials susceptible to UV damage, such as passes.
Although protection is the primary goal of glass, displaying a work of art is the ultimate goal of framing it. Therefore, most glass does not look the best showing the artwork behind it. The visible light transmission is the primary measure of 'transparent' glass, as viewers actually see the light, reflected in the artwork. The transmission of light from the glass is essential in art framing, as light passes through the glass twice - once to illuminate the artwork, and then again, reflected from the artwork, as color - before reaching the viewers.
Transmission of light (for this article, the visible spectrum between 390 and nm and 750m is considered) through the glass is removed either by light reflections or the absorption of light from the glass material. Total light transferred through a glass material (light transmission) is reduced by reflection and/or absorption. In art framing, the reflection of light causes glare, while the absorption of light can also cause the transmitted color to be blunt or distorted. While this type of glass substrate will affect the absorption of light glass, surface treatment can affect light scattering, light reflections and in some cases, light absorption. There are various glass options to achieve this goal as described in the following sections on the Glass Type of Framing the Drawings.
Maps Picture framing glass
Image Frame Type Glass
Regular (or "Remove")
Due to its wide availability and low cost, Soda Lime Glass is most often used for picture framing glass. The thickness of the glass usually ranges from a thin 2.0 mm to 2.5 mm. Clear glass has light transmission ~ 90%, ~ 2% absorption, and ~ 8% reflection. While the absorption can be reduced by using low iron glass, the reflection can only be reduced by an anti-reflective surface treatment.
Low iron (or" Extra-Clear, "" White Water, "etc.)
Low iron, or water-white glasses, are made with special iron-free silica, and are generally available only in a thickness of 2.0 mm for framing image applications. Because low light iron glass absorption can be as low as 0.5% vs ~ 2% for clear glass, light transmission will be significantly better than clear glass. The low iron glass has a light transmission of ~ 91.5% and 8% reflection.
Glass Laminated
Glass coated offers break resistance and protection from harmful damage to art glass. The most commonly used configuration is Glass PVB Foil Glass. Some variations of foil and glass thickness can offer breaking and breaking resistance or even bulletproof. The absorption of laminated glass depends on the glass substrate and foil used in the lamination process. The reflection of laminated glass is similar to that of monolithic glass, unless surface treatment is applied to reduce reflection.
Acrylic
Some types of acrylic glass can have high light transmission and optical quality of glass. Acrylic is also lightweight, compared to glass, and breakproof, making acrylic an attractive option for framing great works of art, greatness. In general, acrylic sheets are scratched easily and retain static charges, which can be a problem when framing pastels or charcoal. Some manufacturers, adding dyes to acrylic glass to filter UV light transmission, and its surface can also be treated with both anti-static and anti-reflective coating.
Glass Surface Treatment and Coating
Due to changes in the refractive index, as the rays move from air (refractive index ~ 1) into glass or acrylic (refractive index ~ 1.5) and then back into the air, this transition causes part of the light to be reflected. While "anti-glare" (aka "non-glare" or matte finish) focus glass treatment on light scattering, the "anti-reflective" layer actually reduces the amount of light, reflected from every glass surface, which has the benefit of increasing the amount of light transmitted through the glass.
Matte (Engraved, "Non-Glare," or "Anti-Glare")
The main purpose of matte glass is to convert spekular reflections into reflection shadows. The so-called "scattering" of reflected light reflects a blurred image, so different shapes and light sources do not distract from the viewing experience of art. Light scattering does not reduce the reflection or absorption, which remains at the glass substrate level. There are several ways to make matte glass surfaces - from pressing patterns when the glass is soft until etching smooth from the glass surface by acid. The quality of matte glass is usually determined by a factor of shine or fog factor.
Anti-Reflective Layer
Single-Layer
The single-layer anti-reflective coating aims to achieve a refractive index of 1.25 (half between air and glass), and can be made either by a single layer micro-porous structure achieved by etching, hybrid material and other processes suitable for producing large-coating area for art framing purposes. A single layer layer has been used as a low cost alternative to multi-layer anti-reflective coatings. A single layer anti-reflective coating can reduce light reflections to as low as 1.5%.
Multi-Layer
To reduce the amount of harmful radiation of light that is transmitted through glass, some glass coatings are designed to reflect or absorb the ultraviolet (UV) spectrum. The following technologies are used to reduce the amount of UV from achieving artwork:
- Organic UV Absorber is added to an inorganic inertial silica-based inertic layer to produce a UV layer absorbing on one side of the glass. Organic UV absorber is able to block nearly 100% UV radiation between 300 to 390nm, but in industrial environments it is difficult to make UV cut sharp without affecting the visible spectrum, therefore UV absorbers tend to also increase the absorption of visible light. A chemically deposited UV absorber also produces a less scratch-resistant surface than a UV-solute or sol-gel blocker, as evidenced by the manufacturer's recommendation to avoid environmental and other contacts with UV-coated sides.
- UV Blocker Interference is usually built into a stack of thin, anti-reflective films, and focuses on maximizing UV reflection below the visible light limit. The industry-grade sol-gel process offers up to 84% UV block, while the AR/UV-block magnetron barrier layer can block up to ~ 92% without adverse effects on the transmission or absorption of visible light.
- UV Filtering of Substrate is possible by adding a UV filtering agent during substrate production. While clear float glass blocks are typically ~ 45% UV radiation, the addition of CeOx to glass has been shown to further reduce UV transmission as well as the widespread use of organic UV blocking dyes in the production of acrylic substrates. Most soda-lime glass fully absorbs short-wave UV-B radiation below 300nm. Low iron glass usually blocks ~ 12% UV radiation between 300 and 380 nm.
UV Protection in Art Glazing
UV Definition in Art Framing
The most widely used "UV Light" definition in the framing industry has been defined as the average transmission without weights between 300 m and 380 nm, while the ISO-DIS-21348 standard for determining irradiation determines the range of UV rays:
The definition of the upper limit of UV protection as 380 nm by the framing industry is inconsistent with the standards received above.
According to the Library Department of Preservation of Congress, art damage does not stop at 380 m, and all radiation (UV, visible, IR) has the potential to ruin the art. Thus, calculating the simple average of all wavelengths between 300 m and 380 nm does not take into account the fact that different wavelengths have the potential for damage to different artworks. There are at least two other methods, which provide a more holistic measurement of radiation damage from both the UV and the visible part of the spectrum:
- Krochmann Damage Function (KDF) is used to assess the glass's ability to limit fading potential. It states the percentage of UV and part of the visible spectrum from 300 to 90 ° that passes through the window and weights each wavelength in relation to the potential damage that can cause the typical material. Lower numbers are better.
- ISO-CIE Damage-Weighted Transmission (ISO) uses the weighting function recommended by the International Commission on Illumination (CIE). The spectral range is also weighted and extends from 300 nm to 700 nm.
For the purpose of frame framing, it is not appropriate to use this method for absolute ratings, since the "Better" rating is obtained with lower visible light transmission, which is not desirable aesthetically in the framing glass. However, by incorporating more damaging factors of art than UV radiation between 300 nm and 380 nm, this method provides a more holistic relative relative tool. For example, comparing 99% and 92% UV Blocking glazing, will translate to 44% and 41%, respectively, under KDF.
How much UV filtering does glass have to have
Discussion of how much UV filtering is required in complex and controversial art framing is driven by conflicting corporate interests. So far no independent organization, not bound by corporate sponsors, has presented scientifically and conclusive verifiable evidence for the amount of UV filtration required for glass for both screens and at the same time protects a work of art. On the one hand, this problem is complicated by the varying amounts of destructive light that actually exist in the indoor environment (from low-level indirect sources to direct sunlight). On the other hand, with the fact that not only the UV, but also the light seems to ruin the artwork. According to the National Fenestration Rating Council, only 40% of the fading works of art are caused by UV radiation. The remaining damage comes from visible light, heat, moisture and chemical materials. This means that increasing the visible light transmission by an anti-reflective coating actually increases the amount of harmful radiation in a work of art.
One of the most comprehensive and independent studies conducted by the US Library of Congress in an effort to showcase and preserve the US Declaration of Independence. Initially, it was decided to use a special yellow "Plexiglass UF3", which removes the ultra-violet and blue tip of the visible spectrum, with significant disruption, but is acceptable for viewing. Sealing the display with a chemical inert gas such as nitrogen, argon or helium also helps its preservation. In 2001, the US Declaration of Independence was revised to include multiple layers of glass for breaking resistance, with a sol-gel-based anti-Reflective coating on the outer surface to improve document visibility.
From the evidence above, it can be concluded that if conservation is the only goal of glazing, then only climate-controlled dark rooms will offer the best protection for a work of art, which can be exhibited every few years, while no glass at all gives perfect display options. Therefore, for the artwork, chosen for display, the ideal amount of UV blocking should be wherever possible, without affecting visible light transmission.
Control UV Lighting within
While determining how much UV light should be filtered by art glass, it may also be important to consider the amount of UV light present in the room or building. Note that ordinary window glass filters out most UV light, which comes from the sun.
The relative amount of destructive light in equal amounts of light:
The above shows that the level of damage even direct sunlight coming from the horizontal skylight is reduced by up to 36% by ordinary window glass. Because of the changing sun position, even less light directly enters through side windows and hanging artwork away from direct sunlight reduces exposure to potentially damaging direct sunlight.
Indoor lighting, especially fluorescent lighting, is thought to contain some UV rays. GELighting.com confirms that "UV exposure from sitting indoors under fluorescent lights at typical light office level for eight hours working hours is equivalent to more than a minute of sunshine exposure in Washington DC on a sunny day in July.In addition, the relative damage of incandescent lamps is 3 times less than fluorescent light.Because UV screening glasses do not protect against all the damage factors, it is important to display framed artwork in a well-controlled environment to reduce the effects of heat, moisture, and visible light.
See also
- Professional Picture Framers Association
References
Source of the article : Wikipedia
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