The appearance of an oil soot particle will be dependant on the length of time the oil droplet is exposed to heat. Droplets start out as liquid spheres and, as they become "hung up," they loose the liquid, develop blowout holes and take on a lacy appearance.
Stereo micrograph of oil soot spheres showing various stages of combustion. Note the "blow out" holes.
Polarized Light Microscope
Oil soot particle using different lighting technique. The left image was taken with reflective light, and the right with transmitted light.
R. Cheng A.S.R.C.
Scanning electron micrograph of oil soot particles. Most of the liquid has been burnt up, leaving a carbonaceous skeleton.