Commentary for Negaim 13:10

היה עומד בפנים – within the leprous house.

If he was standing inside, and he stretched his hands outside, with his rings on his hands, if he stayed [inside] as much time as is required for the eating of half a loaf, they become unclean.
If he was standing outside, stretching his hands inside, with his rings on his hands: Rabbi Judah says that they are unclean immediately, But the sages say: only after he leaves them there as much time as is required for the eating of half a loaf.
They said to Rabbi Judah: if when all his body is unclean he does not render that which is on him unclean unless he stayed there long enough to eat half a loaf, when all of his body is not unclean, is it not logical that he should not render that which is on him unclean unless he stayed there long enough to eat half a loaf?
Today's mishnah continues yesterday's topic: how long does it take for things which he wears to become impure in a house afflicted by a nega.
Section one: The person himself is impure immediately upon entering the house afflicted by the nega. The rings on his hands become impure even though they are outside the house. This is because his hands are part of his body and it is as if they are inside the house. However, the rings don't become impure until he stays in the house the amount of time it takes to eat half a loaf of bread. This is the same as the rule in yesterday's mishnah.
Section two: In this case he stands outside and remains pure (because his head and body didn't enter the house see mishnah 8), but he stretches his hands inside while wearing his rings. Rabbi Judah says that this is like the situation of simply bringing rings into a house. As we saw in yesterday's mishnah, in such a case, the rings are impure immediately.
The other rabbis hold that the rings must stay in the house for at least the length of time it takes to eat half a loaf of bread. They argue that in section one, where his entire body was impure, the rings had to stay on his fingers (although they were outside of the house) for at least that amount of time. All the more so, if his body remains pure, the rings must be in the house for at least the amount of time it takes to eat half of a loaf of bread.

ופשט ידיו לחוץ וטבעותיו בידיו – here we are speaking that his rings are on his fingers like he wears them, and if he delayed in order to eat a piece of bread, they are impure, for they are clinging to his body, but if they were in the palm of his hand in the manner of burden, the Tosefta (Tractate Negaim, Chapter 7, Halakha 9) proves that they are impure immediately.

בזמן שאין כל גופו טמא – as for example, here when he stands outside and he is not defiled all the while that he did not put his head and the greater part of his body inside.

אינו דין שלא יטמא מה שעליו עד שישהה כדי אכילת פרס – And Rabbi Yehuda states, we found that the power of something impure to protect is greater than the power of something pure to protect, for an Israelite when they become susceptible to impurity, they protect vessels in the leprous house, for they don’t defile until he remains enough time to eat a piece of bread, but the heathen and cattle which are not susceptible to receive impurity, they do not protect vessels in a leprous house, for the clothing that is upon them are impure immediately. But the Halakha Is not according to Rabbi Yehuda.