One of the things that you can do with oil slicks if you are shooting digital raw, and have something like Lightroom – is individually tune the brightness of each color, which is what I did here to try and make it as contrasty as possible. No can do with b&w film. No can do if you are shooting b&w jpg. The ability to tune the intensity / hue etc. of colors in a black and white photograph is one of my favorite Lightroom “tricks.”
In this shot I just wanted to accentuate the swirl effect, but in other digital shots I will use it to fine tune the brightness say of someone’s shirt in an image. It has to be used with care because you can remove too much color information and get more noise than you had in the original raw file. But so what – just hit reset and start over again.