Finn's swords

Finn's Sword may refer to either of three swords that Finn has used in Adventure Time.

Gold Sword
The Gold Sword was Finn's weapon of choice through most of seasons one and two. The blade was made of gold, but was dented, chipped, and dirty due to overuse and lack of proper maintenance. Its hilt was black with some worn leather grip-straps, and a red stone in the pommel (possibly a ruby). When the Businessmen were working for Finn and Jake, they polished the sword and sharpened the blade.

In the episode "The Real You," the sword passed through the Bubble Creator, becoming a four dimensional sword. However, when Finn used it to destroy the black hole he had made, the sword was destroyed. Finn is then without a sword until the episode "Mystery Train," when he obtains the Root Sword.

Root Sword
After the destruction of the gold sword, Finn began to use a new sword with a twisted, root-like hilt as his primary weapon. (The name "root sword" is non-canonical.) He obtained this sword in the baggage compartment of the train in "Mystery Train." He then used it in the beginning of "Belly of the Beast" when he fights the Giant. It is seen briefly in Mortal Recoil when Finn throws it at Ice King.

Sword of the Dead
This is the sword Finn used to defeat Marceline's Dad in "It Came from the Nightosphere." Finn drew the sword from the grasslands before his battle and used it to slash open Marceline's Dad, freeing the souls of Ooo. Finn dropped the sword while reciting the incantation to open a portal that would return Marceline's Dad to the Nightosphere. Finn did not keep the sword at the time because he still had his original Gold Sword. The Sword of the Dead has not appeared in any episode since.

Trivia

 * If the stone in the pommel is a ruby, then it may be possible that Fionna's sword is a reference to it, as her sword is made entirely of ruby.
 * In reality, a sword made entirely of 24-karat gold would be a very poor weapon, as pure gold is extremely soft and malleable by nature. A gold blade would stand no chance against steel. Furthermore, gold is very heavy, which would make Finn too sluggish to fight efficiently. Although it is possible that the sword is a gold alloy or even gold-plated, gold in itself is a terrible choice for bladesmithing.
 * The Gold Sword may in fact be enchanted. As seen in "The Silent King " and "The Eyes," it has the ability to deflect fire and ice magic.
 * The Root Sword may have been a gift from Jake, since he planned the "murders" aboard the Mystery Train and knew that Finn's Gold Sword was destroyed in "The Real You."