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In the question Pregancy Test on Shabbos a notion was raised in an answer that the chemical reaction is a problem due to tzovaya.

So what are the boundaries of this, in terms of chemical reactions being a problem, with the specific question of those glasses that dim in sunlight, and become dark like sunglasses. This is a reversible chemical reaction, and I have always wondered if it applies.

As a possible side note/question, what are the boundaries of tzovaya as would mixing vinegar and baking soda to make a volcano on Shabbos be allowed? A chemical reaction that makes a mess...

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    I suggest you split the volcano question off into a separate question: it really is quite separate.
    – msh210 ♦
    Jun 20 '11 at 17:09
  • msh2010: Good point, leaves me with two excellent answers, and I cannot accept both. However, minor question, probably not worth doing it.
    – geoffc
    Jun 20 '11 at 19:12
  • With regard to the first part, don't we generally allow certain forms of Melachah if it isn't permanent (disappearing ink for medical uses in Israel, although still a problem MiDeRabbanan for others), and especially if it's part of the function of the thing (like a folding chair not being a violation of Boneh, or a self-winding watch)? This is a comment, not an answer, because I'm unsure.
    – Seth J
    Jun 20 '11 at 19:17
  • Also, someone wearing the glasses isn't causing the graying, although he could be responsible for it by walking outside.
    – Seth J
    Jun 20 '11 at 19:20
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I saw an excellent comprehensive article on exactly this topic

It brings down all the opinions and reasons, but the bottom line is that these photo chromic lenses are permitted on shabbos.

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    cmb, welcome to the site and thanks for this sourced answer. I hope you stick around and enjoy the site; you may also wish to register your username, as that will afford you a better site experience.
    – msh210 ♦
    Feb 10 '12 at 15:45
  • Great link! excellent info - thanx! the other articles there (in that column) by that author are also very interesting and comprehensive!
    – user1248
    Feb 12 '12 at 14:43
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Rabbi Moshe Feinstein allowed the photo grey lenses, though others disagree.

For more on the theory behind this, see this excellent article from the Star-K's Rabbi Mordechai Frankel (based on the ruling of Rabbi Moshe Heinemann). It discusses the related question of diapers that change color when wet.

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  • Dead link.............
    – Double AA ♦
    Aug 24 at 18:07
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Rav Shmuel Wosner zt"l addresses this in Shevet HaLevi, cheilek dalet, siman 23, os 5. He says that going out in the sun in such glasses is not considered an act of tzoveya.

בענין המשקפים שבאור השמש נעשות כהות אם מותר ללכת בהם בשבת - לבי נוטה יותר שמותר. ובמק"א נחזק זה אי"ה בראיות

With regards to glasses that the light of the sun makes go dark; if it is permitted to go in them on Shabbos - my heart is more inclined to permit it, and in another place we will strengthen this with proofs.

Rav Pesach Eliyahu Falk zt"l in Mechazeh Eliyahu, siman 65 (2nd paragraph in left column) brings this topic when talking about the halachic nature of thermometers and whether that also is a concern of tzoveya on Shabbos when taking a temperature reading. He brings the teshuva from Rav Moshe Feinstein (noted by @Shalom) which can be found in Igros Moshe, OC cheilek 3, siman 45 and says that there, Rav Moshe ruled that the blackness rises within the thickness of the glass and that there is no colour change fading at all but rather it is like coloured paper that sits behind the glass. However, he does question this as he asks that when the colour darkens/tints/fades there must be some form of tzoveya. He therefore concludes that it must only be tzoveyah derabbanan as the colourisation doesn't stay forever and that would perhaps be means to permit it.

Rav Shlomo Zalman Auerbach zt"l is also in the camp to permit such glasses. He refers to it in a footnote in Shemiras Shabbos Kehilchaso, Vol. 1, 18:18 (photo below of the English edition) enter image description here

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There is no problem of Tzoveya with food. Regarding photogrey glasses per this link it is allowed. http://www.revach.net/article.php?id=2497

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Tzovaya translates to coloring or dyeing something. I can't really see how a baking soda and vinegar volcano would be a problem at all with tzovaya.

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There is a really funny story regarding this question. Basically it boils down to an argument between Rav Elyashiv and Rav Shlomo Zalman Auerbach.

See here for the story: http://books.google.co.il/books?id=mxf2QDFNvcYC&lpg=PA265&ots=XhCH9pRwV7&dq=elyashiv%20auerbach%20eyeglasses&pg=PA265#v=onepage&q=elyashiv%20auerbach%20eyeglasses&f=false

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    Doesn't come up for me (gives an error message that the page is unavailable). Would you mind summarizing the story?
    – Alex
    Feb 10 '12 at 18:15
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    @Alex I see it. In short, R' Eliyashiv's daughter married the son of R' Shlomo Zalman Auerbach. She once came to an optometrist who suggested her to buy photo-gray glasses. Since her father in law and father disagreed on whether these glasses are permitted, she was unsure whether to buy them or not. When the optometrist asked her why she can't make up her mind, she said that while her father was of one opinion on the matter, her father in law had a different one. The optometrist looked at her and said "Who cares what your father or father in law think, go ask a posek!"
    – ertert3terte
    Feb 10 '12 at 18:44
  • Yes, I heard this story brought down by Rabbi Hanoach Teller who, if I recall correctly, was close with the Auerbach family and was one of Rav Auerbach's biographers.
    – Bruce James
    Dec 27 '12 at 19:42
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Harav Yitzhak Yosef Shelit"a is Matir (Y"Y KS"A 320:20).

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There are many reasons why photogray glasses are not Tzoveya (see "the 39 Melachos", by R.D Ribiat):

  1. Its not really dyeing
  2. Its regular use of the glasses (derech tashmisho)
  3. Its not permanent
  4. etc.
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