Gemara

7b (Rabah): If one was Mekadesh a woman with silk, we need not appraise it.

(Rav Yosef): The silk must be appraised.

Version #1: If he said Kol d'Hu (any amount), no one requires an appraisal. They argue in a case when he told her that it is worth 50, and it is. Rav Yosef requires an appraisal. Since women do not know the value, if it is not appraised, she lacks Semichus Da'as (a firm decision) for Kidushin.

Version #2: They argue also about Kol d'Hu. Rav Yosef holds that Shavah Kesef (something worth money) can be Mekadesh like money only if it is Kayitz (has a known value), like money.

8a - Support (Rav Yosef for himself - Beraisa): If a man said 'I give this calf) for Pidyon ha'Ben (to redeem my firstborn son)', this does not work. If he said 'I give this calf (or this garment to Ploni) for five Sela'im for Pidyon ha'Ben, it works.

Even though it is worth five, if he does not fix its value, it is unlike money.

Rejection: Really, it is not worth five. The Kohen accepted it in place of five.

The Halachah is, silk need not be appraised.

Rishonim

The Rif and Rosh (1:8) bring Version #1, and rule that silk need not be appraised.

Rambam (Hilchos Ishus 7:18): If one told a woman 'you are Mekudeshes to me with these garments, that are worth 50', and they were of silk and similar things that women desire, if they were worth 50 she is Mekudeshes from when she took them. We do not say that she is not Mekudeshes until they are appraised in the market, so that she will rely on what he said.

Question (R. Tam, brought in Rosh): Why did we need to rule like Rabah? We hold like Rav Yosef against Rabah in only three places (Bava Basra 143b), and this is not one of them! Some say that this rule applies only in Bava Basra; Kesuvos 74b refutes them. Also, why did the Gemara say 'the Halachah is, silk need not be appraised', and not 'the Halachah follows Rabah'?

Answer (R. Tam): Only silk need not be appraised, for its value is roughly known. People do not err so much about it. The value of other things, e.g. gems and pearls, is not known, and people err greatly about them. This is why the custom is to be Mekadesh with a ring without a stone. If one was asked to make a ring and added something of his own, she is Mekudeshes (48b). The case is, the addition was appraised, or its value is roughly known, like silk. A case occurred in which a man was Mekadesh with a Kuchla stone, and afterwards Rav Chisda gauged whether or not it was worth a Perutah. This refers to a blue stone, not a gem.

Rebuttal (Rosh): This does not explain why we remove the stone from the ring. In the first version, all agree about Kol d'Hu (no appraisal is needed). We do not normally assess the Kidushin ring!

Ran (DH ha'Hu): The Rambam connotes that silk does not need appraisal, for she desires it and resolves to be Makneh herself. Things she does not desire so much must be appraised. R. Tam says that people do not overestimate the value of silk so much. Often, people greatly overestimate the value of gems. Even if he did not say that they are worth 50, rather, Kol d'Hu, even Rabah requires appraisal. This is why they discussed silk.

Beis Yosef (EH 31 DH u'Mah she'Chosav Rabeinu): Normally, we follow the latter version. If so they argue about Kol d'Hu! However, R. Tam clearly rules like Version #1, in which Rav Yosef is concerned for her Semichas Da'as. Rabah argues only about silk. In Version #2, they argue about whether or not Shavah Kesef must be Kayitz. We do not distinguish silk from gems. This explains the Rosh's question. However, it is not difficult if we explain R. Tam like the Ran (that gems must be appraised even in a case of Kol d'Hu).

Answer #2 (Ri, brought in Rosh): We needed to rule like Rabah, because Rav Yosef brought proofs for himself. The Gemara did not say 'the Halachah follows Rabah', for in Version #2, Rabah argues about Kol d'Hu; he could agree that if he said '50', it must be appraised. Therefore, it taught 'silk need not be appraised.'

Poskim

Shulchan Aruch (EH 31:1): If one was Mekadesh with an object Stam, it need not be appraised first to see whether it is Shavah Perutah. She is Mekudeshes if it is Shavah Perutah. Even if he said 'you are Mekudeshes to me with this item worth 50', and they did not appraise it first, if later we find that it is worth 50, she is Mekudeshes.

Beis Yosef (DH u'Mah she'Chosav u'Mihu): Rashi says that 'Kol d'Hu' is 'for whatever it is worth.' The Ran says that he was Mekadesh her Stam.

Gra (1): The Ran and Rashba say that Kol d'Hu must mean Stam. If not, the Beraisa of Pidyon ha'Ben does not support Rav Yosef according to Version #2. Tosfos and Rashi say that the support is only according to Version #1.

Shulchan Aruch (2): Some say that if he was Mekadesh with things of unknown value that people err greatly about, such as gems, and he said 'be Mekudeshes to me with this stone worth 50', it must be appraised, for she wavered.

Chelkas Mechokek (2): According to Rashi, she is not Mekudeshes at all. According to the Rambam, she is Mekudeshes only after it is appraised.

Rebuttal (Beis Shmuel 1): Perhaps the Rambam said 'we do not say that she is not Mekudeshes until they are appraised' to teach that no appraisal is needed in that case, but when it is needed, he agrees that it does not help after Kidushin! The Maharit says so.

Shulchan Aruch (ibid.): Some say that if even if he was Mekadesh with a stone Stam and did not say 'it is worth 50', it must be appraised. This is why the custom is to be Mekadesh with a ring without a stone.

Rema: The custom is to ask the witnesses under the Chupah whether the ring is worth a Perutah, so she will know that she is Mekudeshes with only a Perutah in it. Also, our custom is to cover the face of modest Kalos, and they are not particular about what he is Mekadesh her with.

Beis Yosef (DH Zeh...): The Rashba (Teshuvos Chodoshos 163) says that (even though our custom is to give a gold ring), if her face was covered, even if he gave a silver ring not plated with gold, she is Safek Mekudeshes. It seems that if an adult accepted Kidushin herself and did not see the ring, she is Vadai Mekudeshes. To avoid Safek, he should be Mekadesh her again. He need not take back the ring first, for it is a deposit. The Mordechai (Reish Kidushin) says that if he said 'be Mekudeshes to me with the gold in the ring', she is Mekudeshes even if it has a stone, or if we suspect that (it is gold plated and) underneath it is tin or lead. She relied only on the gold in it.

Chelkas Mechokek (6): If one said 'this is worth only a Zuz. I sell on condition that you have no claim of Ona'ah (overcharging) against me', the buyer can claim the Ona'ah. He saw that it was worth more than a Perutah, and knew that the seller merely sought to assuage him. Kidushin is different; we are stringent. Also, she did not give money. Perhaps both intended for Kidushin even if it is worth only a Perutah. We ask the witnesses (whether the ring is worth a Perutah) to avoid all problems.

Beis Shmuel (5): Even though we ask the witnesses, we cover her face lest she see that it is worth more and lack Semichas Da'as.