Hdonly,
I reduced your image to fit on the average screen. Please try to avoid more than about 1024 wide, as it makes people use the horizontal scrolling feature to see everything.
I've actually used that kind of chemical to produce a flat black finish on some aluminum channel stock that I was using as electronics heat sinks. It took me a while to figure out how to get it even. Still, I found that by applying it with a discarded toothbrush and constantly scrubbing to get the loose spots off and replaced with fresh black, I could eliminate the uneven bare spots and pinholes and wind up with coloring that didn't rub off easily. This is going back 20 years, but I also seem to recall I diluted the chemical with three parts distilled water by volume to get time to scrub adequately, but I may be remembering that incorrectly. I do that with a steel blackening product, and I could be misrecalling that I did it with both.
I like the very flat black that results. It is functionally desirable for heat sinks (good IR emissivity), and I use similar chemical blackening on iron sights that I have first abrasive blasted with 400 grit aluminum oxide to give them a good, smooth dark matte surface to react with the chemical. It hangs onto that blasted surface pretty nicely, but it is not as rugged as a Cerakote finish applied to the same sort of surface. You could apply a protective clear coat to it, but then you will lose the flat aspect of it and will be better off just going straight to Cerakote or
Aluma-hyde.