Hello everybody !
I decided to scrub my cast iron after it got some rust on it. After a vigirous rub, spots appeared.
Any idea what the silver dots are ? They seem like little cracks.
Thank you for your time and help !
these are cracks, in the seasoning. you'll need to re-season. cook a bunch of bacon in the pan, wipe out the pan but leave a thin layer of fat. stick it in the oven at 500F for about half an hour. the oven will get a bit smokey but that's ok. you're carbonizing the fat. let the pan cool, wipe it out and repeat every time you make bacon. you could also use coconut oil, lard or beef tallow. (lots of places on the internet suggest crisco or canola oil but... just don't)
here's a more thorough step-by-step http://whatscookingamerica.net/Information/CastIronPans.htm
It's hard to be sure but cast iron starts out a gray or dull silver. It turns dark as it "seasons" and gentle cleaning leaves the seasoning so the pan is as non-stick as possible and less likely to rust or tarnish. My skillet is pretty black; after each use I rinse with hot water, scrubbing with a gentle scrubber, and then dry and apply a light coating of oil/grease.
My guess--and that's all it as with the quality of your photo--is that you accidentally scrubbed off some of the seasoning and exposed "raw" cast iron. If that's the case, oiling it and using it will gradually restore the seasoning as long as you don't scrub too harshly.
Season that bad boy! (: It happened to me after my roommate scrubbed ALL of my cast iron down to the shiny... Some of them were fixed and others were never the same. Yours should be fine after seasoning it.
& be sure to care for it to avoid rusting so you don't feel the need to give it a scrub down in the future!