Because of a diamond's special optical proportions, when light travels into a perfect diamond, 100% of the light travels back to shine through the face of the stone (1).

In an imperfect diamond (2), the light hitting a feather is reflected and we can see the imperfection.

Under extraordinary pressure, the Yehuda clarity enhancement process inserts a microscopic amount of colorless, stable material into the diamonds feather. This material has the same optical properties as a perfect diamond. Following the Yehuda treatment, when light travels into the diamond it passes through (3) the feather and the diamond looks clear and beautiful.

The Yehuda enhancement is performed on a molecular level and the microscopic amount of material that is used ADDS NO WEIGHT to the diamond, according to the Gemological Institute of America (G.I.A.).