Shabbat: Thermochromic Mug



Am I allowed to use this mug on Shabbat?

It turns from black to a picture when you put hot water in it.



  1. Some authorities permit it, as nothing intrinsically changes when the hot water is added to the mug – see Shu”t Yad Dodi page 149:30 by Rav Dovid Feinstein. Other authorities permit it only if the color changes but not if a picture or writing appears. In any event, it is not something that should be done for entertainment on Shabbat. Even those who permit it, only do so when the mug is to be used for drinking hot drinks.

    Best wishes from the Team