What is ultra-clear glass? How is it defined?

Ultra-clear glass is a type of soda-lime-silicate glass with extremely low iron (Fe) content. It achieves ultra-high light transmittance and low color difference through strict raw material purification and process control. Its core feature is that the visible light transmittance is ≥ 91.5% (at a thickness of 6mm). As ordinary glass shows a green tint due to Fe²⁺, ultra-clear glass is required to have no obvious greenish hue at the edges.