If somebody tries to sell you cheap reflective glass saying it is “Hard Coated”, the first thing you should ask is “Is it spray hard coat or CVD hard coat?”. Spray hard coat could be termed as a primitive and is relatively cheaper, in this one the chemical composition is sprayed over glass which would be in a semi solid stage (online process). Most cases, the coating tends to be uneven and deposition rate would be poor. In most cases the coated side appears yellowish.
CVD (Chemical vapor deposition in atmospheric pressure) on the other hand is far superior and the latest. Here, the chemical composition is vaporised and then allowed to deposit on semi-solid glass (online coating) in a controlled manner, achieving high deposition rate and the coating would be even. In most cases, the coated side would have a silver appearance.
It would be a disaster if spray coated glasses which come at cheap rates are used (especially when it is mis-sold with the name “Hard coated reflective glass”) in buildings. Below are some pictures for reference.
Espace rolin fortis, Brussels- Stopsol Silverlight
Hard coated or pyrolytic coated reflective glasses are those in which the coating is applied when the glass is manufactured,i.e. it is an online coating process. In this process of coating, the glass is fused into the glass at 650-700 degree celcius, and on cooling, the coating becomes a part of the glass.
Primary advantage of hard coated glass is the durability, it could also be handled like normal/annealed glass, could be easily heat strengthened, toughened, laminated or curved. These glasses could also be used in single glazing without any fear of losing the coating. Soft coat glasses (to be discussed in the next post) are susceptible to scratch and degradation over time, and requires special handling, hard coated glasses were invented just to counter this problem. Only disadvantage is the variety of colors available when compared to off line coating. Continue reading →