Low-Iron Glass Explained: Why Optiwhite™ is the Clear Choice

Category: Glazing Guide / Home Aesthetics
Reading Time: 6 Minutes

When you look through a window, you assume you are seeing the world exactly as it is. When you install a glass splashback over a pure white wall, you expect it to look white.

However, standard glass is not actually “clear.” If you have ever noticed a distinct green tinge on the edge of a glass table or window pane, you have witnessed the inherent limitation of standard glazing.

For homeowners and architects seeking absolute clarity and true colour representation, the solution is Low-Iron Glass. In this guide, we explain why standard glass isn’t clear, and why premium products like Pilkington Optiwhite™ are the industry standard for high-end applications.

1. The Science: Why is Standard Glass Green?

All glass is made primarily from silica sand. However, the raw materials used in the standard “float glass” manufacturing process naturally contain impurities.

The culprit responsible for the green tint is Iron Oxide (Ferric Oxide). Even in trace amounts, iron oxide absorbs light at the red end of the spectrum and toward infrared, resulting in a greenish-blue hue that becomes more pronounced the thicker the glass gets.

2. The Solution: What is Low-Iron Glass?

Low-iron glass is precisely what it sounds like: glass manufactured using carefully selected raw materials with a very low iron content. The manufacturing process is more demanding, requiring higher temperatures and specialised sand.

While standard clear glass typically has an iron content of around 0.10% (1000ppm), high-quality low-iron glass reduces this to approximately 0.02% (200ppm).

The result is an “extra clear” glass that is practically colourless, offering unparalleled light transmission and neutrality.

Visual Comparison: The “Edge Test”

The easiest way to spot the difference is to look at the exposed edge of the glass pane:

• Standard Glass: The edge will appear dark green, sometimes almost black in thicker panes.
• Low-Iron Glass: The edge will appear pale blue or practically clear.

Left: Standard Float Glass (Green Edge). Right: Low-Iron Glass (Clear Edge).

3. Pilkington Optiwhite™: The Market Leader

At KJM Group, we prioritise quality. When it comes to low-iron glazing, the market leader is undoubtedly Pilkington Optiwhite™.

Optiwhite™ is renowned for its excellent clarity and colour neutrality. By removing the green cast, it ensures that the true colours of the view outside your window, or the objects displayed behind the glass, shine through undistorted.

It also offers superior performance metrics. Because it contains less iron, it absorbs less solar energy, allowing for higher passive solar gain—free heat from the sun—which can be beneficial in cooler climates.

4. Standard vs. Low-Iron Performance Data

The difference in clarity isn’t just subjective; it is measurable in Light Transmission (LT) values.

5. Key Applications: When Clarity Matters Most

While low-iron glass is a premium product, it is essential in specific scenarios where the green tint of standard glass would ruin the aesthetic:

• Kitchen Splashbacks: If you paint the back of standard glass white or cream, the green tint will turn it mint green. Low-iron glass is mandatory for true whites and pastels.
• Retail Displays: Jewellers and museums use low-iron glass so products are displayed with perfect colour accuracy.
• Premium Architectural Glazing: For large picture windows framing a view, low-iron glass ensures the landscape is seen exactly as nature intended.
• Glass Balustrades: In frameless applications where the thick edges are visible, low-iron glass provides a much cleaner, modern aesthetic.

Frequently Asked Questions

See the Difference Clearly

Don't let standard glass distort your vision. If you are planning a project where true colour and maximum light are essential, ask the KJM team about upgrading to Pilkington Optiwhite™ low-iron glass.

Contact us today for a consultation