CSGO's knives are prized by casual players and collectors alike, but the ultra-rare Fire and Ice patterns on Marble Fade knives are particularly popular.
Part of what makes the Fire and Ice combination so rare is that it can only appear on four types of knives: the Karambit, Bayonet, Flip Knife, and the Gut Knife. Since neither of the Flip Gut knives are very popular, this means that any Karambit or Bayonet knives that have this pattern are worth even more. The Talon knife can also have what looks like a Fire and Ice pattern, but it technically doesn't reach what many collectors consider the true pattern.
Marble fade knives can show off three main colors on the knife blade in yellow, red, and blue. How much of each color is shown on the blade is determined by a random number called the pattern index. The index is randomly rolled when the knife is opened from a case, and only a certain index will create a true Fire and Ice pattern. In the pattern, the only colors that appear are red and blue, giving the index its famous name. Even more importantly, a knife must only show these colors on the "play side," which is the side that faces the player in-game.
In the picture above, there is no yellow on the Karambit's blade, making it an authentic Fire and Ice pattern. Some Fire and Ice patterns can have a little bit of yellow near the handle and are usually called "Max Fake Fire and Ice." These are more common than the pure split between red and blue, which is the real true Fire and Ice, but the skins with a hint of yellow are still very rare regardless.
These differences can affect the price of a knife substantially. This is best seen on the Talon Knife, where it's impossible to find a pattern without at least a little bit of yellow on the blade. Due to the yellow, the Talon cannot have a full Fire and Ice pattern.
Luckily, there's an easy way to tell if a CSGO knife has a rare Fire and Ice pattern. By using the pattern index, called the "pattern template" in the CSGO client, users can simply inspect any knife and compare the pattern index to the template below. Here are all the pattern indexes for both bayonets, Karambit, Flip, and Gut knives that are considered by the community as Fire and Ice patterns.
Players can check what patterns they have in-game by inspecting a knife and looking at the "pattern index" under the information tab in CSGO's inspect screen.
These are some of the rarest knives in Counter-Strike, and some collectors will pay a lot of money for a true Fire and Ice knife. Some are listed at more than $1,000 on third-party CSGO skin sites, making them almost as expensive as other rare skins like the Butterfly knife Doppler and even the famous Dragon Lore skin for CSGO's AWP.