The High Energy Transmission Grating Spectrometer of the Chandra X-Ray Observatory is a high spectral resolution instrument utilizing gold X-ray transmission gratings. The gratings have been subjected to a rigorous program of calibration, including testing at synchrotron facilities for the purpose of refining and testing the grating model. Here we conclude our investigation of the optical constants of gold, extending it below 2 keV to complete the coverage over the Chandra energy range. We investigate the carbon, nitrogen, oxygen and chromium edge structures introduced by the grating support membrane. Finally, we summarize the state of the grating model, identifying those energy regions where the residuals are most significant and suggesting where the model might be improved.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.