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Stained glass artworks can be hung outside. Stained glass windows were originally designed for use as architectural art, and as such, the exterior surface of stained glass was always intended to withstand the elements. Faux stained glass windows do not last long when left outside.
Stained glass can be found as both freestanding artworks and architectural components of buildings. Glass art brings to mind shimmering delicacy and fragility, certainly not robust pieces intended for outdoor use. This begs the question, how do stained glass artworks fare when pitted against the elements?
The transcendent qualities of light and color captured within the bounds of stained glass art serve the ruthless master of practicality. Never has artwork of such deceptive fragility been so robustly constructed. Although stained glass artworks are designed to last, there is much that homeowners can do to aid in the preservation and protection of stained glass exposed to the elements.
Is Stained Glass More Delicate Than Regular Glass?
Genuine stained glass windows are designed to last for centuries. The world’s oldest stained glass window is found in the German Augsberg Cathedral. This window is a beautifully preserved piece of 11th-century artwork!
Stained glass panes have the same impact and thermal shock resistance as annealed glass. Although the individual glass panes perform equally as well as the annealed glass windowpanes, the structural performance of a stained glass window will differ from annealed glass windows.
In essence, stained glass windows are a mosaic of hundreds of “tiny” glass windows joined together by lead lines. The fragmented nature of stained glass windows is both their strength and their weakness.
Cracking in one stained glass pane will not spread to other glass panes, and thus the damage is contained to an isolated portion of the window.
Over time lead lines, and grout can become loosened, causing individual glass panes to fall out. Proper maintenance and routine repair ensure that this does not happen to beloved stained glass windows.
Heat-strengthened and tempered glass outperforms stained glass with regard to impact resistance and thermal shock tolerance.
Do You Get Outside-Specific Stained Glass?
Genuine stained glass is created by mixing colored metal oxides and minerals with melted glass. The molten glass is then blown into sheets and baked at high temperatures.
This process seals the pigment into the glass, creating a robust glass pane that won’t fade or break when exposed to the elements. In fact, Cumberland Stained Glass claims that stained glass baked at temperatures exceeding 350°C will not fade, even if it is exposed to direct sunlight for 75 years or more!
Faux stained glass created by painting, glazing, or laminating annealed or tempered glass panes does not fare well when exposed to the elements. Many artists have reported color loss and cracking of painted windows within the first five to ten years.
Must Stained Glass Face a Certain Way?
Stained glass artworks may be textured, smooth, or both.
Stained glass windows where both sides are smooth or both sides are textured can be hung with any orientation that makes sense according to the image within the stained glass.
Stained glass with only one textured surface should be hung so that the textured side faces outward. This orientation optimizes light refraction to best showcase the stained glass window’s artistry.
Textured surfaces are more likely to accumulate dirt and grime, making them difficult to clean. Depending on the environment in which the stained glass window hangs, the ease of cleaning may factor into the decision on which way the window is fitted.
What Are the Biggest Outdoor Risks to Stained Glass?
Five common causes of damage to stained glass windows and artifacts are:
- Moisture and humidity
- Wind, rain, and hail
Numerous churches, hotels, and private homes have been the victim of vandalism with regards to their stained glass windows. Although not a natural cause of destruction, intentional vandalism remains one of the primary causes of damage to stained glass windows, especially stained glass windows in places of worship.
Painted stained glass windows or faux stained glass windows have poor tolerance for sunlight. Enamel paints fade more quickly than acrylic paints. However, even acrylic paints will begin to fade and yellow within two to five years.
Moisture and Humidity
Excessive moisture and humidity can result in corrosion and pitting of glass surfaces as well as damage to the window frame and casement.
Wooden window frames are particularly vulnerable to warping when exposed to high humidity levels.
Condensation occurring on the glass can seep into imperfections and flaws in the window and window frame. Sub-zero temperatures will cause the water droplets to freeze and expand, which in turn will cause stress fractures to appear in the glass.
Wind, Rain, and Hail
Extreme weather, in any form, can cause severe structural damage to stained glass windows. Strong winds buffeting the window panes can cause critical loosing of the window panes, resulting in individual panes of glass falling out.
Torrential rain, hail, and wind can blow tree branches and rocks into windows. All windows, including stained glass windows, will break and shatter when hit with a tree branch!
Glass is not flammable but will suffer structural damage if exposed to high-temperature fires.
Stained glass cannot be tempered and thus is at a high risk of shattering if exposed to thermal shock, a drawback that you have to consider if you are weighing the pros and cons of stained glass windows. Thermal shock is the rapid expansion and contraction of glass when subjected to alternating high and low temperatures.
Glass appliques and painted stained glass windows will peel and warp when exposed to low- and high-temperature fires.
How to Protect Stained Glass Outside
As the guardians of magnificent stained glass windows, homeowners and curators work hard to preserve these fantastical pieces of art from vandalism and the elements.
Protection from Ultraviolet Rays
Genuine stained glass windows do not need protection from UV rays, although double glazing with a UV filter on the outer glass will provide protection from the sun.
Painted stained glass windows are particularly vulnerable to UV damage. UV damage to stained glass windows can be prevented or delayed by ensuring that:
- The correct paint is used.
- Ensure paint is layered thickly. Thinly applied paint has a shorter lifespan than paint with five or more layers.
- The window is hung so that its painted surface is positioned toward the interior of the building.
- Seal the paint by heat treating it in a kiln or oven.
- Apply a UV resistant varnish once the paint has dried.
- Retouch paintwork as needed.
It’s important to properly ventilate stained glass windows. Good ventilation prevents condensation by raising the temperature of the stained glass above the dew point. One method of doing this is through isothermal glazing.
For isothermal glazing, a protective sheet of glass is placed in front of the stained glass window, and vents are cut into the top and bottom of either the stained glass window pane or the outer clear glass window pane.
The vents have a chimney-like effect as they circulate air through the interior space between the stained glass window and the transparent outer glass. Air circulation allows normalization of the air temperature with the atmospheric temperature and thus prevents droplets of water from forming.
Double and triple glazing stained glass windows with tempered glass units are an ideal solution for preventing mechanical damage from the elements. Even if the outer layer of glazing is damaged, the internal stained glass window will be preserved and hopefully left undamaged.
It is much easier to replace a standard pane of tempered glass than a one-of-a-kind stained glass window!
Routine Maintenance and Repair
Routine maintenance and repair are vital to the preservation of stained glass windows.
Replacing lead lines and grout as and when needed will prevent the senseless loss of individual windowpanes. Ensuring that window frames remain sealed and waterproof is vital to the prevention of glass and wood warps.
Cleaning the stained glass windows prevents the accumulation of dirt and grime, which prevents the widening of existing cracks. Smoothing and beveling small cracks in historic windows prevent them from extending into structural cracks. Small cracks in modern stained glass windows are repaired by adding a filler and sealant material.
Vandals are deterred by contracting with a good security company and avoiding leaving your home and property vacant. Would-be vandals are less inclined to target a home when the occupants are visibly present.
The installation of secondary glazing may also prevent damage to stained glass windows. A laminated glass unit is installed on the outer surface of a stained glass window casement and acts as a protective barrier.
Laminated glass will break when hit, but the interior plastic coating prevents the shattered pieces from falling apart.
Stained glass windows can be protected from thermal shock if encapsulated in a tempered glass unit.
Tempered glass absorbs the heat from the fire, protecting the stained glass window from excessive thermal stress. Even if the stained glass window shatters, the humans will be protected as the glass shards are contained in the interior space of a triple-glazed unit.
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