To find the max heat settings for using spacers/covers on your stove with your pans, you'll need to experiment with parchment paper standing in for your silicon covers/spacers. Then just get the silicon cover/spacers with the highest ratings. What you need to know is how high a power setting you can set each burner and still use a spacer/cover.

There is no exact way to do this. For one thing, watts do not really translate neatly into temperature ratings. How hot a pan will get on induction will vary with the pan you are using. Pans vary in construction and materials. Some pans will get hotter and get there faster than others, too.

Anyway, you want to get the highest temperature tolerance range in the silicon. It would be too easy to make a gawdawful mess if you guessed wrong about using a cover with silicon rated for a lesser temperature range.

Obviously, you never, ever want to use boost with a pan while using a silicon spacer/cover. This may be intuitively clearer if you think of your 3500 W boosted induction burner as the equivalent of 25k BTU gas burner. (If you want to do the math to compare effective BTU power to effective induction power, theinductionsite.com has a formula on the "how induction works" page.) Clearly, you wouldn't even think about putting a silicon sheet in cast iron pan over a 25k btu gas burner cranked to max . That's essentially what you would be doing with boosting a pan over a silicon cover. You can heat that cast iron pan to well over 600°F, hot enough to melt lead. And silicon pads.

At least, on induction, if the temp goes much higher than 550° - 600° for any length of time, the overheat safety circuit on most induction units will shut it down until it cool offs.

Using parchment paper for the experiments will get you in the ball park for the power settings and (of course) will be a lot less expensive and much less messy than experimenting with silicon pads. . If one power setting (say, 6 or 6.5) results in scorching --- which is okay --- but power setting 7 causes actual charring, then 6 or 6.5 will be the max you want to use on that burner when using spacers. It might be higher or lower on your Bosch stove.

Silicon can take somewhat higher temperatures than parchment, so this test gives you a margin for error.

I would recommend against using newsprint or paper towels for this kind of experimenting. In my own experiments some years ago, I found that they scorched and charred more readily than parchment.

Oh, and for the folks who do not know what we're talking about here, induction allows you to put spacers between the hob and pan that protect the ceramic cooktop surface from scratches when using rough surface pans such as traditional cast iron fry pans.

Yup, here's what my silicon mat looks like after two years of using it on the largest burner on my Bosch induction cooktop (under either a lodge cast iron pan or a larger ceramic pan). Let me know what you learn!

Thanks to both!

jwvideo, "Obviously, you never, ever want to use boost with a pan while using a silicon spacer/cover." Nope, wasn't obvious to me at all, so I'm glad you mentioned it. I'm brand new to induction stoves. Thanks also for the tip about parchment paper. I tried my own unscientific method of boiling water using boost, then quickly lifting the pot and using a heat sensor on the bottom of the pan. It shows me less than 200, so it wasn't a very good test.

I hadn't really thought that cast iron would get hotter. So you've probably saved me from making a big melted silicone mess. I'll try the parchment method.

Will heating the parchment to the scorch or char level damage my glass top?

No.

If you get really gonzo, and actually catch paper on fire, it may leave a smudge/smear that requires use of one of the readily available smoothtop cleaning/polishing creams like Ceramabryte and Weiman's brands.

It would be rude to ask how I know about this with two different brands.

Technically the hob doesn't get hot. The pan does.

I routinely (always) use silicone rubber pads under my pots and pans. And I always start eggs boiling under boost and use boost for various other temporary heating tasks, such as bringing a large pot for spaghetti to boiling. Boost is not the issue. Pan temperature is the issue. All power transferred by the hob coil goes to the pan and not to the silicone or the Ceram glass cooktop. Pans get hot and transfer heat by conduction back to the silicone pad or pads. Some conduction from the pad to the glass occurs, some convective heating of the air under the pan occurs, and some radiation from the pan to the glass occurs, all of these modestly raising the temperature of the glass.

So long as no cooking is performed at temperatures higher than threshold smoking of peanut oil (450F), the silicone pads (if cut from the high temperature rated silicone) will not be affected. It is when a pan is accidentally heated without water or sufficient food for too long at a high power level that the pan base passes the silicone damage temperature threshold and the pads start deteriorating. (So too would any food in the pan start deteriorating.) In such a case one has to replace the pads by cutting out new pads from the silicone sheet that one is using for a source.

Now, there are a few underlying details that should be noted. Most high temperature silicone rubber has historically been colored red oxide. Other colors of high temperature silicone can now be found however. (See for example the MSC catalog at mscdirect.com.) I am unaware of any clear silicone that is rated at the 450F and above range. In the image above, a clear reinforced silicone is evident. It may only be rated for baking cookies. I await any data the poster has on this particular mat. In any case, I favor a different way of supporting the pans with silicone pads.

If three or four small pads cut from a larger sheet are used (scaled to pan size), the pan has less thermal contact with the glass underneath and the glass temperature does not rise anywhere near the temperature of the pan. The hob glass is only uncomfortably hot under my egg pan after two minutes of boost to boiling and 10 minutes of half-power controlled boiling. I haven't tested the glass temperature under a grilling pan. I would expect some potential for burns, but nothing like a radiant coil surface would reach.

Bottom line: Cook within the safe cooking temperatures of food and the silicone rubber pads supporting the pan will not char or deteriorate. Walk away when you shouldn't on a pan heating up at too high a rate and you will start damaging the silicone. In my post disaster investigation experience, if a pan gets too hot for the silicone, by the time the silicone has given up the ghost the hob has shut down due to pan radiant heat heating the thermal sensor at the center of the hob coil. Failed silicone rubber will have darkened, thinned, and appear limp relative to its initial flexibility. I've never had a silicone rubber "goo" problem with any family cooking mistake.

kas

Kas, I have no data at all, I was hoping you'd provide it! These were cookie baking mats that I started to use on the induction cooktop to keep from scratching the top. I had no idea there were silicon mats and then there were silicon mats until I read some of your threads on here. Where does one get the mats with higher temperature ratings? Here's a page with details on the mat I used. Does that tell you anything?

>>>" In my post disaster investigation experience,.." <<<

Despite my being a follower of that great Canadian philosopher, Red Green --- author of the mantra, "If it ain't broke, you weren't trying" --- I've never managed to reduce a Silpat or Exopat or other silicon baking mat to goo on an induction top, either.

Others apparently have.

http://ths.gardenweb.com/discussions/2255056/warning-silpat-induction-and-wok-do-not-mix

sjhockeyfan: My present pads were sourced by hunting on the Internet for 'silicone cookie sheet' and picking a package that looked like the red oxide type. I'll check the brand name when I find the package. However, in jwvideo's supplied link, I seem to have once specified it as: "The pad being used was the Sili Gourmet silicone bake liner, by William
Bounds, Ltd. These are all-red silicone (no transparent part)."

If I wanted some ASAP, I would order silicone sheet directly from MSC. This page will get you started:

http://www.mscdirect.com/browse/tn/Raw-Materials/Rubber-Sheets?searchterm=silicone+sheet&navid=4287921519

[Some of the descriptions on this page seem to be at odds with either their pictures or other parts of their descriptions, so it is best to go to the source, the better organized "big book" (linked to from any example on that page).]

Basically, I consider there to be two primary options. On "big book" page 1729 the 1/16-inch by a square foot of 40 durometer material MSC Part #: 31938707 will cost $22.47 for 500F service, while on page 1730 the 1/16-inch by a square foot of 40 durometer material MSC Part #: 82428681 will cost $40.59 for 600F service.

Harder rubber seems to be the same price in each type, but I think 40 durometer should be fine unless a really heavy pan with bottom ridges is intended to be used on a very small pad. I don't have a durometer tester to test my existing silicone rubber.

There will be some shipping cost.

A fair number of one-inch to two-inch diameter circles or squares can be cut from a square foot so a square foot should support several disasters.

With respect to an argument I noticed at the thread jwvideo linked to, for steel woks the peanut oil temperature should be very close to that of the pan outer skin temperature at the top of the silicone rubber pad. For cast iron, however, the thermal resistance of the iron is not as good and the pan is typically thicker, so there could be a slightly hotter pan outside surface than pan inside surface. I would still doubt that the outside would be over 500F unless the peanut oil is really being burned off. One may want to provide margin for such a case if it applies by buying the more expensive 600F silicone rubber sheet.

kas