The Separ
The Separ is a device made of wood and crystal. It was created by an organization called Kala Shana long ago to fight against a sort of parasitic hive mind known as "the Dark Bubbling." The Separ was brought to Puddleby by Kala Sahar, a member of that order, in 544.
It works by separating the parasitic dew from its host, causing it to be coughed up. The dew will grow the longer it's inside a host--some exiles who had been dewed for years turned out to have palidews inside them. The wizard Qual had been hunting the Separ for some time, and stepped up his attacks through early 545 until he was un-dewed himself on the 8th day of Summer, 545.
According to Kala Sahar, the Separ is passed from one guardian to the next in order to combat the Dark Bubbling. When she passed it to Dr. Tessa Malthus, Sahar indicated that the Doctor was the 267th guardian. This lends support to the theory that the Separ is quite old.
In addition, Qual claims that the Separ already existed when he was dewed almost 400 years ago. Qual may not be the most reliable source of information, particularly where the Separ is concerened, but this is additional confirmation of the Separ's great age.
Dr. Malthus allowed me to study the Separ for several zodiacs during late 545. I was able to confirm that the Separ is indeed quite old--it appears to be at least 500 years old, and could be even older. The type of wood used in the handle is unfamiliar to me, which makes it difficult to be more precise.
The Separ is quite simple to use. Dews react to its presence by causing their host to shiver uncontrollably, which alerts the wielder of the Separ to the presence of a dewed person. To remove the dew the wielder need only equip the Separ and walk up to the dewed person--even the shortest contact is sufficient. I am including a compressed visionstone of myself undewing Zex to illustrate how the process works.
Besides its use in undewing people, the Separ may also be used to destroy the Dark Bubbling itself. It isn't completely certain yet that this is true--Qual, after being undewed, said that it was, but he is somewhat lacking in credibility. At any rate, the "nest" of the Dark Bubbling remains inaccessible to exiles, and until that changes there's no way to know for sure.
The Puddleby Encyclopedia has a slightly outdated entry on the Separ.