Hands down, the best. Historically, clear glass has been the clearest glass product on the market. Today, we know that iron (Fe) in glass formulations presents a green color cast in clear glass. Some manufacturers may have a little more blue or a little more green depending on their formula. The quality of clear float glass is measured via a measurement of visible light transmittance, not color. In fact, we do not know of any glass manufacturer who will warrant a specific color of clear glass. It makes sense if you have ever seen a float line. If not, take a look at the following link. GANA Videos: Float Glass Manufacturing Process. Into that large crucible of molten glass goes a few basic ingredients. Controlling variation of color when dealing with those large quantities and heat is just hard to do. Where ICD's color matching soars is our ability to compensate for those color variations that come from the glass manufacturer, and attain the color you want on the substrate of your choice for spandrel and interior applications. Having said that, the green in the glass is still there. It also varies, to a large degree, from batch-to-batch of clear glass lots from the same manufacturer.
For many dark colored spandrel and wall-cladding glass, this matters less. Well, it mattered less 20 years ago when light transmittance was low, and spandrel coatings were very dark. Today, glass products transmit far more light than ever, and they are continuing to transmit more as we wish to have more daylight in a building’s vision glass. More light transmittance and a green color cast do not work so well with pastel or white spandrel, for example. With a pastel, the green in the glass may be a stronger color than the minimal amount of colorants used to make a pastel spandrel. With white, to compensate for the green glass, red colorants have to be added to the white coating, so the green color is canceled out. What this results in is dirty looking glass color. Again, there is a vast difference between what OPACI-COAT-300® can do with pastels/whites on clear glass when compared to competitive products on the market. Even with that, the colors produced aren’t as pure as they would be without green in the glass.
That is, until low iron glass, such as PPG’s Starphire®, became so prevalent on the market.
Look at these color chip differences with our OPACI-COAT-300® Primary White on various glass substrates. It is quite striking.
OPACI-COAT-300® #0-0186 Light White or #0-0020 Snow White
(Not shown but redder) on clear float. Red pigment with white in the coating results in a dirty white.
Still, not a bad white, but not perfect.
OPACI-COAT-300® #0-1060 Primary White on PPG Starphire® Ultra-Low Iron Glass
Best white you can find for float glass.
OPACI-COAT-300® #0-1060 Primary White on clear float glass
Notice the green color cast.
Hands down, nothing, beats our OPACI-COAT-300® Primary White on PPG’s Starphire®. There is a very slight color cast, all low iron products show a very slight color, but it is so small it doesn’t matter. What also makes our white so good is the product is applied after tempering. Heat, especially the heat of tempering glass, changes color. The heat required to fire a frit on glass changes the color of the frit. This is why you see a vastly different color before it’s fired. It happens to all colors, all pigments or colorant. The greater the heat, the greater the difference. The how is very interesting, but better for another post. The basics are like heating up an iron rod; it turns orange while hot. Then back to the iron rod color when cooled. The reason we see it as orange is due to different wavelengths of light reflecting back in the hot stage vs. the cold stage. During this, chemistry is happening, electrons are moving around, ejecting, and resettling. With an iron rod, when cooled, it doesn’t appear to change much in color between the pre-heated and cooled stages. But in some pigments, the heating process changes the color and then again when cooled. Often not going back to the same color after it’s cooled. Again, it’s all about chemistry and a great topic for the future. It happens, just something to know.
is applied post-tempering and either air or low oven cure; resulting in next to no change from applied to cured stage. Couple that with a low-iron glass product, like
, and you get the most pure pastels and whites you will ever find.