A new primary specular gloss standard has been developed at the National In
stitute of Standards and Technology to overcome the disadvantages of black
glass. This new standard is a high-purity BaK50 glass with good mechanical
durability and homogeneity. In addition, the index of refraction n(D) = 1.5
677 is close to the value specified for the theoretical standard, and the d
ispersion characteristics are similar to black glass.