When I was in Ner Israel forty five years ago, the Mashgiach was Harav Dovid Kronglass. (Reb Dovid was a gadol in Torah and mussar. He wrote his sefer Divrei Dovid on Zeraim while he was in Shanghai, and he was, as far as the human mind could tell, a tzadik gamur. He said the second Beis Medrash shiur, after which you would go to Rav Rudderman's shiur klali, and some of the baalei kishron tried to avoid his shiur by staying two years with Rav Kulefsky and skipping him, because he eschewed fireworks in favor of crystalline clarity.) I once heard him say that when he began his work as a mashgiach, he thought that the picture was Torah, and seder, order, was the frame around the picture. He said that he came to realize that the picture is seder, and Torah is the frame. Sometimes, I think I understand what he meant. For one thing, I believe that when you have a safek in halacha, and you ask for a psak, or, if you know the sugya you pasken for yourself, the most important thing is not figuring out what the ultimate truth is. What's most important is that when you have a safek, you seek an answer from the Torah. The process is more important than the result. The word Halacha, perhaps, refers to the halicha to find the answer. After all, the word הלכה stems from בחוקתי תלכו, which refers to the discipline of seeking knowledge.
Also, you have the Rashi in Menachos 7a. Rav Avimi learned Menachos in the Beis Medrash of Rav Chisda. The Gemara asks, but Rav Chisda was a student of Rav Avimi! The Gemara answers that Rav Avimi forgot that masechta, and he needed Rav Chisda to remind him of what he had forgotten. But why didn't he send for Rav Chisda to come to him! Because going to him is more effective.
רבי אבימי תני מנחות בי רב חסדא ואבימי בי רב חסדא תני והאמר רב חסדא קולפי טאבי בלעי מאבימי עלה דהא שמעת' בא להכריז רצופין ל' יום שני וחמישי יג] (ושני) ס' יומי אבימי מסכתא איתעקרא איתעקר ליה ואתא קמיה דרב חסדא לאדכורי גמריה ולישלח ליה וליתי לגביה סבר הכי מסתייעא מילתא טפי
מסתייע מילתא. משום יגעתי ומצאתי
The next part of this discussion is directly related to this. It won't seem to be relevant, but it will eventually tie Miodownik's book and lehavdil Reb Dovid's observation to the dinim of Tevillas Keilim. Patience.
Our parsha teaches the dinim of tevilas keilim in Klei Midyan (going with the great majority of the Rishonim and poskim that it is deoraysa.) The Torah mentions six metals: את הזהב ואת הכסף את הנחושת את הברזל את הבדיל ואת העופרת. There is a machlokes among the poskim whether all metals are deoryasa, or only the ones listed. Obviously, aluminum is not listed, as it was not isolated and refined until the late eighteen hundreds. The Tiferes Yisrael in his introduction to Taharos says that all metals are deoraysa. Many later poskim, such as Reb Moshe, disagree and say that only the ones listed are. Nowhere does the Torah say the word מתכות in the context of Tevilla or Tumah, and having mentioned six types of metals should make it a שני כתובים הבאים כאחד. Reb Yaakov Kaminetzky in his Emes L'Yaakov in our parsha distinguishes between Tevilla deoraysa and Tuma deoraysa. (More marei Mekomos on this topic in the post pasted below.)
Last fall, I posted the following regarding Zirconium knives. There, as here, I highlight the futility of defining materials neatly as one thing or another. I am copying that post to this one, where it belongs.
Ceramic Knives and Tevillas Keilim: Do ceramic knives require tevilla?
Earthenware does not need tevilla. Metals and glass do. Ceramic dishes are the subject of some discussion, (שאלת יעבץ א, סז, פת"ש יו"ד קכ, ב say no; ערוה"ש קכ, כט says one should be tovel without a bracha because it is similar to glass) and most people are not tovel them. But what we call ceramic knives might not fit neatly into any of these categories. As a result, it is not at all clear whether they need tevila at all, and if they do, whether the tevila is midoraysa or miderabanan.
To address this question you have to know basic hilchos tevillas keilim and materials science. The chemistry issue is that ceramic knives are made of Zirconium Dioxide. This material appears in many forms with very different characteristics. It can be made into imitation diamonds, cubic zirconium. And it can be sintered into knives that are harder than steel. Pure Zirconium is, in the language of science, a metal. As Eli points out, the fact that pure Zirconium is a metal means very little. Pure Silicon is also metallic, but, like Zirconium, does not exist in nature in its pure form. It occurs as Silicon Dioxide- sand- which is definitely not a metal. In halacha, are articles formed from zirconium dioxide metals, and if they are metals, are they included in the metals mentioned in the parsha of tevillas keilim? Or perhaps halacha would categorize them as ceramics, or even glass?
Here is a scientific discussion of glass, ceramic, and pyrocerams.
As I said, even if in Halacha it would be viewed as a metal, it is not clear what its status would be for tevilla. The reason is as follows. According to Din Torah, metallic utensils requires Tevilla. But to say that all metal requires tevilla also is not an explicit fact. It is an extrapolation. The Torah only identifies gold, silver, copper, steel, tin or lead as requiring tevilla. What about metals that are not mentioned, such has aluminum or uranium? There are three opinions. Some say they are obligated mi'doraysa and should be toveled with a beracha, some say with a beracha but only Miderabanan (Igros Moshe- Miderabanan. O.C. 3:58, Y.D. 2:164, 3:22, Divrei Chachachim page 189:3:footnote 37, Chai Ha’Levi 4:56:3.) Others say there is no requirement to tovel them at all, like plastic (Divrei Chachachim page 189:3, Emes L’Yaakov Y.D. 120 footnote 51. But as I mention above, Reb Yaakov holds that it's derabanan only for Tevillas Klei Midyan, but deoraysa for Tuma.) For most people, as a matter of practical rabbinics, it has been suggested that one just avoid the issue and be tovel such metals after one has already recited the beracha on metal or glass.
So even if Zirconium were to be defined as a metal, the question would remain. But I don't think that can be assumed. To the uneducated eye, it is no more glass than metal and no more a metal than ceramic. And we cannot look to what chemists or metallurgists or advertising departments say. We need to prove how it would be categorized according to halacha. Since we don't know the rationale for Tevilla, it is difficult to extrapolate.
The bottom line is that it is so different from each of them, that it really ought to be in a class of its own, like plastic, and one could make an argument that it does not require tevilla at all.
It happens that the status of corelle and pyrex, among other pyrocerams, is also not simple. The crystalline structure of these materials resembles ceramic more than glass. In fact, ceramic is subject to differences of opinion regarding kashrus, some considering it to be glass, but many hold that it is Kli Cheres (מ"ב תנא, קסג), which has very different halachos both for tevilla and kashrus. Porcelain is cheres that is heated to a much higher temperature than usual cheres, to a point where glass is created and flows into the spaces between the clumps of cheres, so it's as much glass as cheres. But at least in those cases, the raw material is the same as cheres and the appearance and smoothness is the same as regular glass. That is not the case here.
Additionally, I think that the determinant regarding Cheres/earthenware for Tevillas Keilim is not identical with that of Cheres/earthenware for Kashrus. For Kashrus, the only issue is its absorbtiveness. The Gemara discusses various utensils that are coated with tar, or made from various earths, and uses simple observation of fact to determine whether they have a law of kli cheres for kashrus. For Tevilla, absorbtiveness is not necessarily a determinant. For all we know, Cheres for Tevilla has nothing to do with be'li'ah, but instead with tumah.
More mar'ei makom on porcelain vis a vis kashrus-
בשכנה"ג או"ח תנא, הב"י ל', כתב שמנהג העולם להשתמש בפורצלאן בפסח, אף שהשתמשו בו בכל השנה בחמץ, שהם כזכוכית. והוא לעצמו החמיר כדברי הרדב"ז, אבל לאחרים לא החמיר. גם בשאלת יעבץ א, סז, התיר. והפר"ח כתב, שגם המקילים היו מקילים בפורצלאן אמיתי, אבל עתה יש מזויפים שבולעים, ולכן לכו"ע צריך להחמיר. וכ"כ מחב"ר תנא, י. והובא בכה"ח תנא, שה. וכן פסק בקול מבשר א, פ. וכן המנהג. אבל בצירוף של ספקות נוספים אפשר להקל, כמובא בדברי האחרונים שנזכרו בס' הגעלת כלים יג, שסח; וביבי"א א, יו"ד ו; וח"ז יו"ד י.
So, I'm sorry to say that I'm left with the default position- one should get a regular metal utensil and take it to the mikva when you're taking a ceramic knife, and make a bracha on the regular metal utensil to cover the ceramic knife. (I don't think glass would be a good idea. Glass is derabanan. A bracha on a derabanan before doing a deoraysa might be a problem in over le'asiyaso and not over de'over.)
Rabbi Dr. Nachum Stone was kind enough to discuss these matters with his Rav, Harav Rabinovich of Maaleh Adumim. Dr. Stone's presentation of the question is particularly important in that he is a musmach, a talmid chacham, and a dentist who is very familiar with ceramics and metals and their chemical and physical characteristics. This is what he reports.
בעניין חומרים חדשים טבילתם והכשרתם
מה דינו של סכין מחומר קרמי –האם זכוכית?
צריכים לבדוק מה זה בדיוק
אבל לגבי טבילה כנראה כמו זכוכית- לחומרא
האם דינו ככלי הכנה בלבד ולא כלי סעודה , ואולי מן הדין אינו חייב אפילו מדרבנן
ייתכן שלא חייב אבל בכל מקרה יהיה טבילה בלי ברכה
לגבי חרסינות חדישות כגון
CORNINGWARE + CORRELLE
חול, כמו כל זכוכית, אלא עיבוד שלהם בחום SiO2 שחומר גלם שלהם הינו בעיקר
המראה חיצונית היא כמו זכוכית אטומה , אבל במבט של
ELECTRON MICROSCOPE המראה
היא של אירגון פנימי
מאד ,מאד מסודר כמו של מתכת.
כשנשברים, זה דומה לזכוכית לכל דבר.
לגבי טבילה והכשרת כלים איך להתייחס לאילו?
להתייחס אליהם כזכוכית .אפשר הגעלה להכשירם. לא יודע למה אומרים 3 פעמים .
Checking on the web, I found the following on a website written by Rav Ovadiah's grandson, Harav Yaakov Sasson, "member of the prestigious Bet Midrash Yechave Da’at in Jerusalem," and based on Harav Ovadiah's psakim. I mention it only because of its simple honesty.
שאלה: האם סכין קרמי חייב בטבילה
תשובה: החומר ממנו עשויה סכין קרמית, אינו מתכת. אך אין לנו ידיעה ברורה ממה היא עשויה, אם היא עשויה מחומר הדומה לחרס, או חומר הדומה לזכוכית, שאז יש להטבילה, או שמדובר בחומר הדומה לפורצליין, שאין חיוב להטבילה. ובכל אופן, נכון להטבילה בלא ברכה.
Now, as in my earlier post, I've some to realize that what we assume are defining characteristics of metals are not definitive as far as the halacha is concerned. The word Mateches is of no use, because it refers to the ability to melt and re-cast the material, which applies to glass, but glass is derabanan. Plastic is no less ductile than metal, while zirconium knives are variously called ceramics or metals, but they don't bend and they're made from a kind of sand. A great deal of a materials behavior depends on its molecular arrangement, and it will someday be possible to make a petroleum derivative polymer that acts like what call metal.
It certainly would be easier to say that although in the world of physics the microscopic arrangement of the component molecules are an essential factor in the behavior of a compound, and maybe that's true in the parsha of Mussar, but in dinei Tevilla and Tumah, what matters is not the structure or behavior, but instead the constituent molecules or atoms, in which case it would be limited to these six and no more.