Optical material: BK7 optical glass
A/R multi-coated on faces,  hypotenuse is aluminized.
Sides and faces  (60x50mm),sides are overcoated w/black paint.
hypotenuse (70x50mm) is aluminized and overcoated w/black paint.
60/40 scratch/dig quality
Surface Flatness: 1/8λ
Angle tolerance: +- 5 arc min