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Anodized metal is metal with an increase in the thickness of the natural oxide layer on the surface of metal parts. Is there any issue kashering it, or is it basically like metal with a layer of rust which in general is a problem only if food particles can get stuck inside the rust (Mishne Berurah 451,22), which is not the case with anodized metal?

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    What is the source for "rust is a problem only if food can get stuck inside the rust" please?
    – Avrohom Yitzchok
    Jan 20, 2016 at 18:27
  • @AvrohomYitzchok citation added
    – Yoni
    Jan 20, 2016 at 19:28
  • I guess some people will be scared to kasher if it is diyed (since the ingredients of the diy might not be kasherable)
    – hazoriz
    Jan 21, 2016 at 19:47

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Look in the Mishna Brura. He explicitly says

אבל כשיש שם חלודה יש לחוש שמא יש שם משהו מן החמץ והחלודה מכסהו ולזה לא מהני הגעלה כי אין הגעלה למה שהוא בעין. וכ"ז בחלודה שיש בזה קצת ממשות (שקורין ראס"ט) שכשגוררין אותה משם יש שם כמה עפרורין שאז יש לחוש שמא יש תחתיה משהו ממשות האיסור בעין והחלודה מכסהו אבל אם אין בחלודה ממשות כלל רק מראה בלבד כמו שנמצא לפעמים שיש שחרות או אדמימות בצד הפנימי של הכלי שאנו קורין (פלעקי"ן) אין קפידא. וכן הדין באותן כתמים הנעשים בכלי בדיל (שקורין ערד פלעקי"ן) שאין מעכבין את ההגעלה כיון שאין בהם ממשות רק מראה בלבד [אחרונים]:

He says that the concern of rust is not that there's a Chatzitza but that there may be a piece of Chametz hiding under the rust. The way you describe Anodized metal, it appears that nothing can get between the oxides and the metal, so there should be no concern

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  • I cite the MB in my question. Rust is oxidized iron and is clearly treated as kasherable. Aluminum oxide and other anodized metals may not be treated halachically as aluminum and other metals respectively.
    – Yoni
    Jan 22, 2016 at 0:04
  • @Yoni you haven't shown any evidence that it shouldn't. If rust = Iron, why shouldn't Aluminum Oxide = Aluminum?
    – ertert3terte
    Jan 22, 2016 at 18:05
  • I fully agree with your premise. וכי מפני שאנו מדמין נעשה מעשה? Aluminum does not naturally oxidize whereas Iron does. So rust make be treated as iron regarding kashering. There are other possible distinctions one might make. Without a source I am not sure. FWIW my friend asked 2 rabonim and got to 2 answers. I answered my friend exactly as you wrote...but I'd like a source if possible.
    – Yoni
    Jan 22, 2016 at 19:41
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You could ask the same question concerning tarnished silver which has a thin layer of silver oxide on its surface.

There is no chiyuv to polish silver before you tovel it because you do not perceive the tarnishing as something seperate to the kli.

The same would seem to apply to anodized metal.

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    Chatzitza for Toveling is different than Kashering...
    – Double AA ♦
    Jan 21, 2016 at 1:45

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