can you clean an oxygen sensor? and how do you read them?

[David Pertuz]

the other weekend I replaced my 6-year-old and cracked Gen3 HS header with
a relatively new Gen4 in much better shape that I picked up last year. My
new header had its own oxygen sensor in it, though of unknown mileage.

Looking at the two sensors, I decided to go with the one in the newer
header - it had a whitish color to it, versus the black on the one I took
out of the car, which has around 70k miles on it.

Can an oxygen sensor be cleaned the way a spark plug can, e.g. in a toaster
oven o tal?

Can I interpret the blackness in the same way as if I were reading a plug?
Sure, soot is caused by a rich condition, but I'm not sure why in this case.

thanks,
david