Why Is a Dual Pane Glass Sometimes Dark?

Broken Seal

• Examine the seal around your dual pane window to check if there is any noticeable damage. Hire a professional window installer or a home inspector to examine the seal since it is difficult for the untrained eye to distinguish whether the seal is broken. Professionals use heat-seeking devices to study the seal and isolate troublesome areas. A broken window seal allows moisture to enter the sealed space, resulting in darkening of the glass. Avoid tampering with a broken seal and don't apply adhesives that could cause further damage.

Mold from Moisture

• Observe whether moisture has entered the space between your dual panes of glass. Look for water droplets, foggy areas or condensation that has accumulated on the interior portion of the glass. If you see visible moisture, mold may have formed between the two panes, causing the glass to appear brown or black. This darkening effect is the result of mold or mildew attaching to the glass or window frame. It is likely that your dual window panes will require replacement.

Silica Haze

• Hire a professional window installer to determine if the silica pellets, located inside the aluminum strip that outlines your window panes, have failed. A silica pellet is designed to absorb moisture from incoming air that leaks into pressurized space between dual panes of glass. According to the International Association of Certified Home Inspectors, "Silica gel has an immense surface area, approximately 7,200 square feet per gram, which allows it to absorb large amounts of water vapor." Over time, moisture enters the space between dual panes and saturates the silica pellets, making them useless against moisture. The result is dark coloration, fogginess and visible condensation that often requires replacement.

Film or Tint

• Inspect the interior pane to determine if the window has a thin layer of film or tinting that causes the glass to appear dark. Some homeowners install plastic film or room-darkening tint on windows to reduce sun exposure. Examine the interior of the window for small bubbles or creases that reveal film or tinting. If you don't want the room-darkening effect, pull at the edge of the film to see if you can remove it. If it does not pull off easily, hire a professional to remove the tint on the glass.