  The mirrors installed on Imaging Atmospheric Cherenkov Telescopes like the
MAGIC telescopes in La Palma, Canary Islands, are constantly exposed to the
harsh environment. They have to withstand wind-induced corrosion from dust and
sand, changing temperatures, and rain. Because of the size of the telescope,
protecting the structure with a dome is not practical. The current mirrors used
in MAGIC are aluminum front-coated glass mirrors, covered by a thin quartz
layer. But even with this protective layer, significant decrease in
reflectivity can be seen on timescales of several years. The quartz layer is
very delicate and can be easily scratched or damaged, which also makes cleaning
the mirrors almost impossible. We have tested a novel design of glass mirrors
that can be easily cleaned and should show almost no degradation in
reflectivity due to environmental influences. The protective layer is a
ultra-thin glass sheet which is back-coated with aluminum, making it possible
to simply wipe the mirror with household cleaning tools. In this contribution
we will present results from laboratory tests of reflectivity and focusing
properties of prototype mirrors, as well as long-term tests on-site at the
MAGIC telescopes. We will also outline plans for exchanging a large fraction of
MAGIC mirrors with this novel design, guaranteeing a peak performance of MAGIC
for the coming years.
