“…At the present time, the indentation of materials with property gradients is relatively undeveloped, especially for indentation with a Berkovich indenter. Therefore, the modulus values presented for the float glass represent a 'composite' modulus of the volume indented and the surrounding material rather than exact values of modulus for a given depth [42,43]. While a gradient in modulus appears to exist, the exact nature of this gradient is currently not available.…”