Background is a little better color, try even darker next time.
The most contrast is best. If you can get enough light on it then try black.
Too bad the edges are not better yet. I have an old "very fine"Lune.
As kcb5150 says the older ones with water(for me) and under 20-25 laps should make it ridiculously sharp.
Off the 20k it will improve sharpness and retain smoothness if laps are limited.