Q&A: A Cup That Changes Color on the Sabbath
Originally published:
This is an English translation (via GPT-5.4). Read the original Hebrew version.
A Cup That Changes Color on the Sabbath
Question
Hello Rabbi,
I have a special cup at home that changes color when ice-cold water is poured into it, due to some kind of chemical reaction. Is it permitted to use it on the Sabbath, or is there a prohibition of coloring here?
Answer
Does the cup itself change color? This coloring is not a Torah-level prohibition of coloring, since you are not applying color to the cup; rather, the chemistry changes its color (as with litmus paper). Beyond that, you are putting in the water not in order to color it, so it is an unintended inevitable result that does not matter to him. In addition, the prohibited result (the coloring) is produced here indirectly. Therefore, in my opinion, this is permitted.
Discussion on Answer
In my opinion, even then it is permitted.
I understand from the Rabbi’s words that if I intentionally chose this cup in order to enjoy the special color created in it by cold water, then it is an inevitable result that is intended and therefore prohibited. (Unless indirect causation by itself makes it permitted?)