Keeping up with my theme of addressing the glossary of terms, this blog is dedicated to the most important term of all – frit. Why do I say it’s the most important? The answer – its importance to bonding glass to vehicle frames and the longevity of that bond.
The frit is the black paint band around the perimeter of an auto glass part. Though it does provide the appearance benefit of acting as a “moulding” substitute to cover the urethane bead, it also has a practical purpose.
For example:
• The black color protects the polyurethane adhesive from one of its biggest enemies, ultraviolet light. Ultraviolet light is found in sunlight and it attacks urethane by breaking it down to a “caulk like” black powder. This weakens the urethane and reduces its bonding strength. 
• The application of the frit paint on the number four surface of the glass adds to its adherence by adding more surfaces to bond to through mechanical adhesion. The rougher the surface the more mechanical bonding can occur.
Back when frit wasn’t applied by the glass manufacturer and urethane was used to bond glass, we applied a “black-out” primer to serve the purpose of the frit. The black-out primer and large, wide chrome mouldings protected the urethane bead from ultraviolet light and the primer acted as the roughened surface for the mechanical bond. Then glass and vehicle manufacturers realized they could add more protection and better bonding by adding frit paint to the glass.
The frit allows for “exposed edge” glass parts, which contribute to eliminating mouldings. The frit also adds more of a mechanical bond, which strengthens the safety devices the glass contributes to, and it makes the car look good.
So, pay attention to that black paint called the frit. It is important. It is not just there to make the vehicle look good. It is there for safety purposes.
