Decorative Silk-Screened Glass for Vision Areas
Silk-screening ceramic frit onto glass lets a designer create a subtle or bold look for a building-using patterns and color. silk-screened glass also improves solar control performance.
Using the same technology as Viraspan spandrel glass, you can incorporate standard or custom colors into a specific design element. Or, you can use one of Viracon's three standard silk-screen patterns (see chart below).
In the past, white ceramic frit has been the predominant color used in decorative applications. However, there has been an increase in the use of dark ceramic frits, such as neutral gray and black for a more subtle, less noticeable look. These colors also help reduce reflection and offer alternative design options without adversely affecting performance.
The first step in silk-screening involves washing the annealed glass. Then, the ceramic frit paint is applied to one side of the glass (see Figure). Next, it is fired within a tempering furnace to create a permanent coating. The glass is always either heat strengthened or fully tempered to prevent glass breakage due to thermal stresses under sunlit applications.
Viracon's silk-screened decorative patterns can be combined with clear or tinted glass substrates, as well as with high-performance coatings to reduce glare and decrease solar transmission.
For an insulating glass unit, Viracon recommends applying the silk-screen pattern to the second surface for optimum solar performance. The sealed air space protects the ceramic frit for easy maintenance, as well as meeting Viracon's long-term durability architectural glass product requirements (see figure above).
Viracon can also apply the silk-screen pattern to the third or fourth surface of an insulating or laminated glass unit. The results are an increase in solar absorption on the interior glass ply and a higher shading coefficient. silk-screening on these two surfaces becomes more apparent from the interior during nighttime conditions, which complements indirect interior lighting.
Furthermore, silk-screened ceramic frit can also be applied to the second, third, or fourth glass surface in a laminated vision glass application (see Figure 1). If you combine laminated glass with other types of glass to form an insulating glass unit, the ceramic frit must be protected within the air space or be applied to the roomside of an insulating glass unit (see figure).
When using silk-screen patterns in architectural building applications, there may be a potential to see a Moiré pattern develop in the glass when viewed in certain light conditions and at specific solar angles. Coupled with these are the inherent dynamics of the construction process.
Moiré is an optical phenomenon that presents itself as a "wavy, rippled or circular" pattern under some conditions. The Moiré image is a pattern formed when two regularly spaced patterns "overlap," but are not aligned. Common examples may be woven fabric and window screens. In this case, the Moiré pattern appears to "shimmer" when light is reflected from the surface.
Architectural float glass will reflect light from each of its surfaces. When silk-screen patterns are applied to the #2 surface of an insulating glass unit, the image is reflected off of the #3 glass surface. It's the interference of the reflected image from the #3 surface, by the silk-screen pattern applied to the #2 surface, that causes the
Moiré pattern. The condition may be further pronounced by the air contained in the air space of the insulating glass unit. Air will expand when heated and contract when cooled. This is known as the Ideal Gas Law. Glass deflection may create the condition necessary for the Moiré pattern to occur, or may further distort the reflected image of the silk-screen pattern. With large glass sizes there is more potential for movement that can create a possible condition for the Moiré pattern effect to occur. Buildings under construction may have a higher potential to exhibit Moiré patterns because the glass temperatures have not been stabilized by controlled temperatures.
While it may be impossible to identify when the potential for Moiré pattern may occur, the following general recommendations may be helpful:
1. Line patterns closely spaced, or two glass surfaces having a silk-screen pattern applied (insulting glass) may be more prone to exhibiting a Moiré pattern.
2. To a lesser degree, silk-screened patterns using dots and holes, closely spaced may also be susceptible.
3. Insulating glass units used in spandrel areas may also be more prone to this phenomenon.
4. Large glass sizes with an aspect ratio (length to width ratio) of less than 2:1.
5. Highly transparent glass (clear, low-e coating).
6. Shadow box applications.
Viracon recommends that a full size mock-up be evaluated on all projects considering the use of silk-screen patterns. The mock-up should be installed at the building site and viewed under a variety of lighting and temperature conditions.