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- Sep 23, 2017
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What Rivem said. Looking at Edmund Optics I see two lens substrates that match color wise the lens you have. One is germanium and the other is silicon.
My guess is that the edge is black painted.
Germanium and silicon - due to a high refractive index, IR lenses are simpler, and mostly singlets. Though, who knows what is that without seeing through. :can:
OP could tell if a lens transmits light. What is a focal length. Can even try to measure radii.