Babetoo: Is it possible that the porcelain is on the outside of the pan and that the inside might need seasoning? I realize that there are some like Le Crueset that have porcelain on both sides...
As For the ridges... I have 3 such pans and am looking to get 1 or 2 more. I have made bacon on my 2 burner grill now for probably 2-3 years now. I can let it sit in Dawn Dish liquid and it wont hurt it. On occasion I will cook a lamb chop or rack on it or maybe a steak. On those occasions I might do the salt trick, I might take a butter knife to it and scrape the grooves out. Sometimes I will take a little Dawn to it because my wife dosent like it when her bacon taste like...something else. Short of that I dont wash it unless it sits for a few weeks and I think it might be rancid. I let it get warm while pre heating the oven for a given weeks bacon, pour off the excess , layer on another 10 or pieces of bacon and season it some more.
On occasion... such as when I have cooked something else on it and I havent washed it, I will use the 10" or 8" grill pan... so I can get them seasoned...
If I happen to think of it, on occasion I will cook bacon on the Pizza pan to get it seasoned... nothing sticks to it either.
Maybe 1 or twice a year I will take my other pans... I think I have 12, slather them with bacon fat or vege oil and fire them for a few hours.
Several years ago when I lived full time on the farm, I would oil my pans up, most of them, one of them I would season a steak up and put it in a pan, on a cold night and stick them straight into the wood stove. I would have a raging orange hot roaring fire going and let that rip. That great thing about cast iron is that nothing will hurt it as long as it covered with oil.
Making Bacon in the Wok was a little weird, but nothing sticks to it...