Improvements in Fire-Protective Glass Increase Color Clarity

Architects have relied on glass ceramics as a fire-protective window glazing for more than 30 years—allowing designs to include more natural light while still protecting the safety of occupants.

But for all of its fire and life-safety performance, glass ceramic glazings have had a trade off—typically an amber-colored cast and higher levels of distortion and haze when compared with float glass.Over the past decade, glass ceramic manufacturers including Vetrotech have incrementally improved the transparency to the point that the natural, but unwanted, color was nearly invisible except when the product was placed against a stark white surface or paired with more transparent float glass, which has a slight greenish tint. Even so, architects and building owners worried that the yellow-hued panes might distort views and sightlines, or appear discolored when compared with nearby windows or doors containing more transparent, non-ceramic glass.

Color rendering

The earth-tone tint is a byproduct of the manufacturing process. During the production of glass ceramics, components of the glass partly crystallize, leaving fine-grain crystals embedded in the glass matrix. When those beneficial crystals are heated, they contract in proportion to the scope and volume of the expansion of the heated glass. The two actions within the matrix negate each other, so no thermal expansion results. No thermal expansion means no cracks.

Still, because the crystals are not as transparent as the glass itself, the matrix takes on the slight amber hue, which can distort the appearance of the color of objects on the other side of the glass. Generally, the darker or more colored the glass tint, the higher the deviation from the actual color of areas or objects as viewed through the glass.

Vetrotech’s latest innovation, Keralite Select, has substantially improved color rendering, reflectivity and clarity. The fire-rated glass ceramic measures 97.1 out of 100 on the color rendering index, which determines how “true” a color appears when viewed through the glass. The color of an object viewed iKeralite Select - The clear choice for fire-rated glass ceramicn natural daylight without any glass between the eye and the object would rate at 100.

These high ratings for color clarity, unheard of a decade ago, meet the aesthetic goals of building design professionals and the decision-makers at schools, hospitals, and commercial buildings who require products that comply with increasingly stringent fire codes and also demand an aesthetic quality comparable to float glass.

To rank higher on the color rendering index, Vetrotech manufacturers have altered their processes in a variety of ways, including incorporating higher-quality, neutral-colored raw materials, like whiter sand, into the manufacture of its glass ceramic product and improving surface-polishing technology. The purer ingredients introduce less contamination and less color into the finished glass, so it more closely matches the visual qualities of standard architectural float glass, according to glass technology experts.

Beyond color

Along with color clarity, Keralite Select improves on a number of other critical factors of visual and aesthetic performance. The patent-pending surface-polishing technology improves the brilliance and reflectivity of the surface, so it appears clearer, lets more light pass through, improves color clarity, and more closely matches non-rated or fire-rated, intumescent products located nearby. Polishing removes the subtle, dull “orange peel” texture that has been a signature of fire-rated glass ceramics and is most noticeable on large panes. Keralite Select has the lowest haze value at 0.5%.

For more information on Keralite Select visit

600450 Improvements in Fire-Protective Glass Increase Color Clarity
Date: 24 September 2014
Source: Vetrotech Saint-Gobain

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