what is its surface quality?
Household-mirror made with float glass may have flatness tolerances as low as 9–14λ per inch, equating to a deviation of 5600 through 8800 nanometers from perfect flatness.
Mirror
Surface quality, or surface accuracy, measures the deviations from a perfect, ideal surface shape. Increasing the surface quality reduces distortion, artifacts, and aberration in images, and helps increase coherence, collimation, and reduce unwanted divergence in beams. For plane mirrors, this is often described in terms of flatness, while other surface shapes are compared to an ideal shape. The surface quality is typically measured with items like interferometers or optical flats, and are usually measured in wavelengths of light (λ). These deviations can be much larger or much smaller than the surface roughness. A normal household-mirror made with float glass may have flatness tolerances as low as 9–14λ per inch (25.4 mm), equating to a deviation of 5600 through 8800 nanometers from perfect flatness. 
what are heavy metals? Metals with relatively high densities and atomic weights. what is its biological role? Period 4 heavy metals are required for certain biological processes. what are its uses? Iron accounts for 90% of all refined metals and platinum accounts for 20% of all consumer goods. what are the exposure sources? Mining and industrial wastes, vehicle emissions, etc. what is the origin and use of the term? Heaviness was noticed in prehistory and early use of the term "heavy metal" dates from 1817. who was behind its discovery? UNANSWERABLE what is its toxicity? Assumed to be highly toxic or damaging to the environment. what is its colouring and optics? Colours of glass, ceramic glazes, etc are produced by chromium, manganese, etc. and high reflectivity of some heavy metals is important in the construction of mirrors. what is the history behind this latter mentioned construction product? Obsidian mirrors of Anatolia was found around 6000 BC, mirrors of polished copper found in Mesopotamia is from 4000 BC, and polished stone mirrors from Central and South America date around 2000 BC onwards.
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Mirror [SEP] Surface quality
Surface quality, or surface accuracy, measures the deviations from a perfect, ideal surface shape. Increasing the surface quality reduces distortion, artifacts, and aberration in images, and helps increase coherence, collimation, and reduce unwanted divergence in beams. For plane mirrors, this is often described in terms of flatness, while other surface shapes are compared to an ideal shape. The surface quality is typically measured with items like interferometers or optical flats, and are usually measured in wavelengths of light (λ). These deviations can be much larger or much smaller than the surface roughness. A normal household-mirror made with float glass may have flatness tolerances as low as 9–14λ per inch (25.4 mm), equating to a deviation of 5600 through 8800 nanometers from perfect flatness.