Explanation: Black spots on white skin or white spots on black skin must be because of a "Nega" -- "blemish" that was there.

Question: Rabeinu Tam asks that in Nazir (31b) the Gemara implies that Rav Chisda is only talking about a black ox among white oxen. The black ox makes them all less valuable. The Gemara there asks from a Mishnah there that implies that the white oxen are less valuable. The Gemara concludes that Rav Chisda is talking about oxen for plowing, where a black ox is less desirable (than a white ox). (Note: This implies that Rav Chisda is not discussing Rashi's scenario of a blemish of the opposite color on one ox.)

Answer: Rabeinu Tam says that Rav Chisda addressed two different things two different times. While here Rav Chisda is indeed referring to black blemishes on white skin and white blemishes on black skin, there Rav Chisda discussed a black ox among white oxen.

It is clear this is correct, as in all of the old Sefarim the text of Rav Chisda's statement in Nazir (ibid.) is "black amongst white is stricken (a blemish)," nothing more.

It is also appears that this is correct for the following reason. If the Gemara there stated both white amongst black and black amongst white, as stated here, and we will explain that it is discussing both a blemish on skin and a blemish of a different color ox among oxen, what is the Gemara's question there? (Note: The Gemara there asks, didn't Rav Chisda say that black amongst white is bad?) How do we know black among white is referring to an ox among (other) oxen? Let us say the opposite is true (it is referring to black spots on a white ox), and the Gemara should not ask anything. This was stated by Rabeinu Tam.

Observation: The Gemara here implies that the Shamir was required to cut the stones for the Eifod.

In Kidushin (31a), regarding the incident of Dama ben Nesinah, they asked him for stones for the Eifod. This was during the times of the second Beis Hamikdash, as it states there that the next year he had born to him a red heifer etc. In the first Beis Hamikdash they never brought a red heifer, as stated (Parah 3:5) that the second red heifer offered was by Ezra. If so, the Shamir was clearly also required in the second Beis Hamikdash.

Implied Question: One cannot ask that in Sotah (48a) the Mishnah states that when the first prophets died, the Urim v'Tumim stopped, and when the Beis Hamikdash was destroyed, the Shamir stopped (existing or being used). (Note: This implies that the Shamir stopped being used after the first Beis Hamikdash!)

Answer: The Mishnah there is referring to the destruction of the second Beis Hamikdash, as is apparent from its usage of the word, "Beis Hamikdash." The Gemara there says, "The first Beis Hamikdash" when it discusses other things there (implying that the term "Beis Hamikdash" by itself refers to the second Beis Hamikdash).

Proof: Additionally, this is evident from the fact that it was not stated together with the first prophets, and it should have said, "When the first prophets died, the Urim v'Tumim and Shamir stopped." "When the first prophets died," meaning when the first Beis Hamikdash was destroyed (they both happened at the same time), is when the Urim v'Tumim stopped.

Observation: It must be that they watched over it from the times of Shlomo until the destruction of the second Beis Hamikdash.

Question: Rabeinu Elchanan asked that in Avodah Zarah (52b), regarding the stones of the Mizbe'ach that the people of Greece desecrated, the Gemara asks that we should break the stones (and reuse them). The Gemara answers that the Torah says, "Whole stones" should be used for the Mizbe'ach. The Gemara asks, why don't we cut them? The Gemara answers that the Torah forbids this, as the Pasuk states, "Do not wave over them (i.e. cut them with) metal." If the Shamir was extant, why didn't they use the Shamir?

Answer: The Ri answers that the Shamir would not make them smooth, which they needed to be, as if a fingernail would be nicked by the stone it cannot be used for the Mizbe'ach. This Gemara is according to the opinion in Sotah (48b) that the Shamir was required for the stones of the Beis Hamikdash. The Pasuk that says, "smoothed with a plane," is referring to the stones used to build Shlomo's house (i.e. palace).

Explanation: (Note: Tosfos is bothered by the fact that they did not ask the Urim v'Tumim.) They did not want to ask the Urim v'Tumim when they could ask in a different manner.

Implied Question: This Pasuk had not yet been written. (Note: How could they have known it?)

Answer: They knew the Pasuk anyway, like the Pasuk, "Cursed is one who does the work of Hash-m with trickery," in Bava Basra (21b) regarding Yoav (where they said the Pasuk before it was actually said). (Note: The Netziv in his commentary on the Mechilta explains that there were often Pesukim that were said to earlier prophets and they became known amongst the world. They were only recorded later, and often in a slightly different manner more befitting that time.)