When I took these cookie sheets from my father's house, they were in pristine condition. My mother had likely never used them. I knew he would never use them either, so with his permission, I took them home. My old cookie sheets were stained and gross. I was determined to take good care of these.
After a few months, my shiny and pretty cookie sheets started getting these weird oily, yellowish-brown stains that just kept getting worse. Plain old blue Dawn, which cures so many other ills, couldn't touch the stains at all. I was considering buying new ones when I found and re-pinned this post this morning. The original blog post is at "One Good Thing" by Jillee. I swear Jillee is a genius--check out her other cleaning tips.
So I had baking soda and peroxide on hand. Both are cheap, so I figured I'd give it a shot. I (liberally) sprinkled baking soda on the worst sheet. Then I squirted some hydrogen peroxide on it. I expected it to fizz, but it didn't. Then I scrubbed. I admit that it took a while to scrub, but I began seeing results immediately, so I continued to scrub. At first I used a dish scrubber I picked up at Target or Walmart or somewhere. Then I used a washcloth. Then I used a scouring pad.
See the results for yourself. These are the photos I took before, during and after the process, so they're in order.