Summary for black optical coatings Discussion
Black optical coatings for 316L stainless steel were discussed as a way to reduce parasitic reflections at about 890 nm. Pere Llosas asked what black coating options exist and where to find information. Ward Barcafer suggested black chromated alkaline zinc, noting he had seen it used on brass laser timing gears for similar optical needs; he added that stainless would first need a Wood’s nickel strike before zinc plating, and that the black chromate process required close control because of high QA demands. Dan Brewer recommended a room-temperature black oxide coating, saying it is not a true black oxide but can give a reasonably dulled, almost matte finish. Another contributor said their process produces a nice black iron oxide coat with a matte finish, used on parts for a UHV vessel after vacuum baking and light cleaning, and pointed to MIL-DTL-13924 as the specification.
Q. I have an application where we need to decrease the parasitic optical reflections on a 316L stainless steel part. The used light is around 890nm wavelength.
What kind of black optical coatings are available?
Do you have any ideas on where I can look for this information?
Thank you for your help.
Pere Llosas
– Switzerland
1999
A. I have seen black chromated alkaline zinc used over brass laser timing gears for an optical timing device which had similar optical requirements. In this case prior to black zinc, a woods nickel would be required in order to zinc plate the stainless. The black chromate had to be baby sat during the chromating operation due to the high QA requirements.
Ward Barcafer, CEF
aerospace – Wichita, Kansas
1999
A. Try a room temp black oxide coating. Although this is not a true black oxide, it should provide a reasonably dulled almost matte finish.
Dan Brewer
chemical process supplier – Gurnee, Illinois
1999
A. We use a process that produces a nice black iron oxide coat with a matte finish. We vacuum bake the parts to use in our UHV vessel. Usually there is some loose amount oxide that we wipe off/lightly sonicate. The specification for the process is:
MIL-DTL-13924
[⇦ this spec on DLA]
For a matte finish that it is vacuum compatible you MUST also specify:
NO OIL, NO WAX, NO SEAL
NO TESTING
Alan Bobalan
– Irvine, California, USA
August 27, 2009