Sometimes odd looking stains show up on a glass-ceramic cooktop. What are the iridescent, silvery, or rainbow looking marks on the burner area? Some people claim these are “inside the glass” and have come for no apparent reason. There is a reason. And that reason is using the wrong cleaners to clean a surface that reaches 1200℉.
Dish soap was not designed for 1200℉ on dark black glossy surfaces! When you clean with dish soap, or any detergent, some of that cleaner remains on the surface after wiping it off.
This past week I was contacted by a consumer from the lovely state of California. She provided a picture similar to the thumbnail photo in this post and stated her relatively new cooktop had a silvery, rainbow looking mark inside the glass burner area and it was getting worse over time. She also stated that she kept the cooktop very clean and only used a mild dish soap with water to clean, and no significant food spills during cooking yet. Was her cooktop defective?
The key comment she made was “dish soap.” Yes mild-mannered dish soap, which is readily available and good at removing grease residue from most any surface, may be the culprit here. Dish soap was not designed for 1200℉ on dark black glossy surfaces! When you clean with dish soap, or any detergent, some of that cleaner remains on the surface after wiping it off. Unless you thoroughly rinse the surface, some dish soap is still on the surface and will get quite “baked” once you turn on the heat! I sent her a sample of a good cooktop cleaner, like shown in my cleaning method post and asked her to try cleaning with this cleaner instead, then get back to me. After a day, she responded with a note of success, the rainbow is no more.With that in mind, I recreated this dish soap mark after 5 or so cycles of boiling water using my test apparatus and some spare CERAN® glass-ceramic. It didn’t take too long. Here’s how I did it:
- Each time I wiped the cooking surface with a sponge soaked in dish soap and water.
- Next, I lightly wiped the surface dry with a paper towel. As with the consumer who contacted me, on occasion the surface was still mildly warm, not hot, and the soap dried on the surface lightly.
- Then, I boiled some water on the recently cleaned surface and let it cool.
- Even after the first cycle, a small rainbow ring begins to form under the pan. The open hot surface does not show this surface mark, only the region under the pan. Keep this in mind as it’s possible the soap residue on the bottom of the pan can also cause this mark to show up.
- After several cycles of wiping with soapy water, wiping, and boiling water, the residue has grown. Note, the pans I used had wavy lines on the bottom surface and those lines are mirrored in the marks on the surface.
- The good news, these marks can be prevented using the correct cleaner. Even better news, a good cooktop cleaner like Weiman or CeramaBryte takes this rainbow off very easily! Here I divided off a small section of the stain with tape, and cleaned it with CeramaBryte. See post on best how to for cleaning.
- The final result, the sectioned area cleaned quite well. I used some “elbow grease” when wiping with the cleaner. It certainly did not just wipe off with no effort, but with some repeated effort, cleaned off fine. Note some the surface effects still visible are only a reflection of the window and sky in the glossy black surface.
If you have something you would like us to test or explain, let me know.