Hi, Dave,
Welcome to the forum.
I don't see how you can reach temperatures higher than 212F in a double boiler. That's the temperature of boiling water. And, while you might increase that a couple of points due to the slight steam-under-pressure syndrome, I doubt it would go near as high as 266.
I would use a candy thermometer, and stir constantly, to avoid burning.
As to pot material, it likely doesn't matter much. Personally, I tossed my aluminum pots long ago. I would suggest either stainless or coated-cast iron for this purpose. If you still own one, nothing wrong with glass, either.
|