Rambam - 1 Chapter a Day

When wood keilim, leather keilim, or bone keilim are broken, they are purified of their ritual impurity. If one then made a k'li from the broken pieces or one collected the broken pieces and made other keilim from them, these are considered like other pure keilim that had never contracted impurity previously and are susceptible to impurity from the time they were fashioned onward.

All metal keilim that are broken after they contracted impurity regain purity. If one melted them down and made other keilim from them, they return to their previous impurity. A metal k'li cannot become utterly pure unless it was immersed in a mikveh while intact or it remains broken.

The return of metal keilim to ritual impurity is a Rabbinic decree. Why did the Sages decree that metal keilim should return to their former impurity? This is a decree, enacted as a safeguard lest a person's k'li contract impurity and he melt it down and make it into a new k'li on that day. If it is considered as pure as is its status according to Scriptural Law, one might come to say: Breaking a k'li purifies it and immersing it purifies it. Just as when it is broken, melted down and fashioned into a new k'li, it is pure on that day, so too, if it is immersed, even though it is intact, one may mistakenly think that it is pure on that day and he will say that it is not necessary to wait until nightfall for keilim to regain purity. Due to this concern, the Sages decreed that they are impure.

Whether a k'li contracted impurity from a corpse or another type of impurity and was then melted down, it returns to its former impurity until the ashes of the red heifer are sprinkled upon it and/or it is immersed in a mikveh.

If a k'li contracted impurity from a corpse and the ashes of the red heifer were sprinkled upon it on the third day and afterwards, it was melted down, another k'li was made from it and then ashes were sprinkled on it on the seventh day and it was immersed, it is still considered impure. The sprinkling before it was melted down is not linked to the sprinkling after it was melted down. It cannot regain purity unless ashes were sprinkled on it on the third and seventh days and it was immersed while it was a k'li before it was melted down or ashes would be sprinkled on it on the third and seventh days and it was immersed once it was made into a new k'li after it was melted down.

The following laws apply when impure iron was mixed with pure iron. If the majority was from the impure metal, it is considered as impure. If the majority was from the pure metal, it is pure. If there were equal amounts, it is impure. Similarly, when mud is mixed with turds and the mixture was fired in a kiln and made into a k'li, if the majority was from the mud, it is susceptible to impurity, because it is an earthenware k'li. If the majority was from the turds, it is not susceptible to impurity.

When pure metal keilim were coated with an impure coating, they are impure. If, however, one fashions keilim from an impure coating, they are pure.

When the thick side of a hatchet was made from pure iron and its blade from impure metal, it is impure. If the blade was made from pure metal and the thick side from impure metal, it is pure. The status of the entire tool is determined by that of the portion with which work is performed.

A pure hatchet that was coated with impure iron is pure.

When the mouth of a pitcher was made from impure metal and its base from pure metal, it is pure. When it was made of pure metal and its base from impure metal, it is impure, because the status of the entire implement is determined by that of the container, for it is the portion with which the task is performed.

When a metal k'li contracted impurity of Rabbinic origin, e.g., it contracted impurity from a false divinity or the like, then it was broken, melted down, and fashioned into a different k'li, there is an unresolved doubt whether it returns to its former impurity or not.

When glass keilim became impure and then broke, they are pure like all other keilim. Even if they were melted down and new keilim were made from them, they do not return to their former impurity. The rationale is that, as we explained, their impurity is primarily of Rabbinic origin. Hence, it was not decreed that they return to their former impurity.

Similarly, if glass utensils were broken, even though the broken pieces are themselves keilim and fit to be used, since they are components of broken utensils, they are not susceptible to impurity, because they do not resemble earthenware keilim.

What is implied? When a glass bowl is broken and one made its base fit to be used as a k'li, the base is not susceptible to impurity, even though it is like a bowl. If one leveled the broken portion and filed it down, it is susceptible to impurity.

When the mouth of a small bottle that can be carried with one hand is removed, it is still susceptible to impurity, because one does not use it by inserting one's hand in it, but by pouring from it. By contrast, when the mouth of a large bottle that is held with both hands is removed, it is pure, because it will injure one's hand when it is inserted within it. Similarly, even though a flask of perfume is small, if its mouth is removed, it is pure, because it would injure one's finger when one removes the perfume from it.

Large pitchers whose mouths were removed are still considered keilim because they are used for pickling.

When the major portion of a glass cup is damaged, it is pure. If a third of the circumference over the major portion of its height is damaged, it is pure. If a hole was made in it and he plugged it with tin or tar, it is pure. When a hole was made in a cup or a bottle, whether in its upper portion or its lower portion, it is pure.

When a hole was made in the upper portion of a large pot or a bowl, it is impure. If it is in its lower portion, it is pure. If such utensils are cracked, but can still contain hot liquids just as cold liquids, they are impure. If not, they are pure.

Cups that have been chinked, even though their rims scratch a person’s mouth, nevertheless, remain susceptible to ritual impurity.

A glass dispenser is pure, because it is like a distributor, for it is not a container.

When a glass item is used as a pane, it is pure, even if it can contain liquids, because it was not made to serve as a container. A glass ladle is considered as a container even though when it is placed on a table, it will turn to its side and not serve as a container; it is still susceptible to impurity.

When a glass pot is made into a pane, it remains susceptible to impurity. If it was made intentionally for the purpose of sight, i.e., that the objects placed inside of it could be seen from its other side, it is pure. All glass utensils are not susceptible to ritual impurity until the tasks to fashion them are completed, as is true with regard to other utensils.