Context: Glass has the ability to refract, reflect, and transmit light following geometrical optics, without scattering it. It is used in the manufacture of lenses and windows. Common glass has a refraction index around 1.5. This may be modified by adding low-density materials such as boron, which lowers the index of refraction (see crown glass), or increased (to as much as 1.8) with high-density materials such as (classically) lead oxide (see flint glass and lead glass), or in modern uses, less toxic oxides of zirconium, titanium, or barium. These high-index glasses (inaccurately known as "crystal" when used in glass vessels) cause more chromatic dispersion of light, and are prized for their diamond-like optical properties.

Question: What can be used to make glass less refractive?
Answer: boron

Question: What is the refraction index of typical glass?
Answer: 1.5

Question: What is a toxic additive that increases refraction?
Answer: lead oxide

Question: What are high-index glasses erroneously called?
Answer: crystal

Question: Why are high-index glasses valued?
Answer: for their diamond-like optical properties

Question: What can be used to make glass less dense?
Answer: Unanswerable

Question: What is the refraction index of diamond?
Answer: Unanswerable

Question: What is a toxic additive that increases optics?
Answer: Unanswerable

Question: What is another name for chromatic dispersions?
Answer: Unanswerable

Question: Why are high-index glasses modified?
Answer: Unanswerable