A little feedback. You may recall that I had a project to quantify colors of metal samples, heat-treated at temperatures from 250°F to 600°F in 25°F increments. The engineer in this project wanted to generate a color accurate chart that would enable his people to assess the temperatures products had experienced in service. The samples were 1-½ inch diameter discs about 3/8 inch thick, and the flat surfaces were polished nearly to a mirror finish. Not only that, but the color after heat-treating was not uniform in all the samples, making a difficult project essentially impossible. I tried photographing the products under controlled lighting conditions with very diffuse light, using multiple setups. I even constructed a light tent in one setup. I used gray cards, color checkers and other known color samples in the shots. As I figured, and as most everyone here suggested, the task is essentially undoable. I can make the metal objects any brightness I want my varying the family of angles, diffusion, exposure, etc. I sent the photos to my customer and explained why the project would only lead his engineers to make incorrect assessments. As suggested here, I recommended that he create a batch of samples and make them available to his engineers, so they could compare the parts to real live samples. He agreed that was the best solution and will proceed in that manner. Thanks for your feedback and recommendations. Lou