The photograph shows an old copper gasket, a common expendable item in ultra-high vacuum applications. It was used in a surface physics experiment and located in front of an ion getter vacuum pump. Over the years the gasket has been coated by a thin layer of titanium dioxide because of the deposition of titanium in the vacuum pump. The colors of the reflected light in the photo are the result of thin film interference, with different colors depicting different layer thicknesses.
<a href="//commons.wikimedia.org/w/index.php?title=User:RHerder&amp;action=edit&amp;redlink=1" class="new" title="User:RHerder (page does not exist)">Reinhart Herder</a> (rherder@web.de)
<span class="int-own-work" lang="en">Own work</span>