The two birch samples depict the effect of a
UVA benzotriazole on a birch panel.
The panel on the right is a control panel,
the one on the left was subjected to the
equivalent of one years harsh sunlight.
The bottom portion was finished with a clear acrylic lacquer with no additive.
The middle is a UVA and the top is a combination UVA/HALS
(Hindered amine light absorber).
UVA's protect light sensitive substrates, while HALS protect the finish --
both from yellowing and light induced degradation like cracking and peeling.
Note the bottom untreated left is yellow/gold, while the middle is the same
color as the control sample on the right which was kept out of light.
So make sure that the UV coating you use has the right one in it,
or add it yourself.
Please note that this is a 1 year exterior exposure test and is rather
harsh as compared to the levels of light that can be expected indoors.
Jeff Jewitt