This is the damage from an old dome skylight on the stairway railing in a house located in Stouffville. Dome skylights give very little UV protection  (UV is what fades things). Most  dome skylights are made of 2 layers of acrylic in the shape of a dome. They are usually sealed one to the other with neoprene gaskets or butyl tape. Unfortunately, they cannot be sealed tight enough to create a vacuum in the same way as 2 layers of flat glass can be sealed. Because they cannot be perfectly sealed, argon gas cannot be injected between the 2 domes. It's the argon gas that is injected between the 2 layers of flat glass skylights that gives the higher level of UV protection. Besides causing fading damage, domes also tend to create a lot of heat in the summer.