There are three classes of relics. First through third.
First class relics are part of the saints body like hair or bone.
Second class relic is something owned by the saint or an instrument of the saints death. In the instance of martyrdom, the instruments of torture.
A third class relic is made when someone touches an object to a first class relic or second class relic.
"§1 It is absolutely wrong to sell sacred relics."
"§2 Distinguished relics, and others which are held in great veneration by the people, may not validly be in any way alienated nor transferred on a permanent basis, without the permission of the Apostolic See."