Summary for diffuse reflective coating Discussion
Diffuse reflective coating/plating is the core issue in this thread: Bob Parker needed a largely Lambertian, 85–90% reflective finish on thin stainless parts for near-IR use at 810 nm, and found that 30 micro-inches of gold was too specular. He asked whether a matte finish could be created by post-baking and how to specify it. Ricardo Burstein replied that the parts must be polished before plating and then brightened after plating to get the desired result, while Tom Pullizzi stressed that the required finish must be specified in advance and handled by the plating shop or another in-house operation rather than left to the plater’s discretion. The discussion does not provide a baking recipe or a guaranteed matte-gold process; instead, it emphasizes controlling the surface finish specification and preparation steps.
Q. We are trying to coat a thin (.003 in) stainless steel part with a diffuse reflective coating. We only need 85-90% reflectance, but it must be largely lambertian. We have tried plating with 30 micro-inches of gold, but the resulting surface is too specular. These are photo-etched parts, and no particular surface finish was specified, other than the etchers standard clean-up, and whatever prep work the plater does. I am told that a matte finish can be achieved by post baking the parts, but have no idea how to specify same. The reflecting is in the near infra-red (810 nm), which is why we tried gold.
At this point I would welcome ANY suggestions.
BOB PARKER
CyberOptics – Minneapolis, Minnesota, USA
A. You must polish the parts prior the plating and bright them after plating to get your desired results.
Ricardo Burstein
Bnei Berak, Israel
A. You need to specify the finish to be achieved before plating, either to be performed by the shop doing the plating, or by another operation in your own shop. You cannot let the plater decide how the part will be finished.
Tom Pullizzi
Falls Township, Pennsylvania