Spot Landing: Determining the Light and Solar Properties of Fritted and Coated Glass

Abstract

The use of ceramic fritted architectural glazing is becoming increasingly popular. “Fritted glass”, which is also known as “enamelled glass”, is defined as glass with a surface covering made of glass frit^[1] that is applied by a printing method and fused to the glass substrate at elevated temperatures. The enamel coating may be continuous or consist of a discontinuous pattern such as spots or stripes. Functional thin-film coatings on glass have been used in standard glazing units for many years to improve thermal insulation or for solar control.  Specification of light and solar properties for these standard glazing types is well-defined and can be calculated on the basis of the algorithms specified in EN 410:2011 or ISO 9050:2003.  This is not the case for glazing that incorporates fritted glass, alone or in combination with functional thin-film coatings.  The paper initially describes the different printing options for fritted glass and the fundamental principles of functional thin-film coatings. When glass surfaces are coated with glass frit, it is essential to note that the light-scattering coatings transmit and reflect incident radiation not only directly but also diffusely. The same applies when functional thin-film coatings are combined with frit coatings. Suitable measurement methods to collect the scattered radiation, measured transmittance and reflectance spectra, and the calculation of light and solar properties on the basis of the EN 410:2011 standard are presented. At the same time, the limits of this standard and the need for its extension are demonstrated.

[1] Frit: a durable mixture of glass and ceramic particles, which may act as pigments.