I want to know the answer to the following question:
What can be used to make glass less refractive?
All the background I'm provided with is that "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.". Is that enough to answer the question?
Answer: yes