Firework Rocket

Firework rockets are items that are launched into the sky by a dispenser or when placed directly on the ground. The color, fade, shape, and effect of the explosion are determined by what ingredients are used to craft the firework star, an optional ingredient used when crafting the firework rocket. If a firework star is not used, the bottle rocket only leaves a trail and disappears with no explosion. Multiple firework stars may be used, in which case they go off simultaneously upon detonation. The height of a rocket can be increased by adding 1 or 2 additional gunpowder to the rocket recipe. Their flight path is random, but always upward, and sometimes are offset up to 5 blocks to any side. While rockets have random paths, they tend to spiral upward. Fireworks are affected by gravity and their motion is affected by any explosion it is in range of, including TNT, creeper explosions, and other rockets explosions. While rockets are affected by flowing water, they are not affected by lava.

There is a delay between detonation and the player hearing the sound, emulating real fireworks, but this sound travels much more slowly than in the real world. Jeb mentioned on Twitter that fireworks may have effects on mobs, such as scaring wolves. There is a bug that, if the firework's explosion is in front of water or ice, the water and/or ice may become invisible for a fraction of a second. A second bug will cause your game to go to an 'End of Stream' page when you set off a firework rocket without a firework star on a multiplayer server.

If a rocket's path is hindered by any solid block it will do one of three things: stay under the block as if caught there until it explodes (more likely to happen if the firework has a shorter flight duration), explode upon contact (if this happens the explosion will appear above the block, even though the rocket did not go above it, unless there are more than one block), or stay under the block for a few seconds then fly off more to the side (more likely to happen with longer duration). If a rocket with any kind of explosion ingredient detonates under a block, the explosion pattern will appear flattened against the ground in a wide, disc-like fashion. If multiple rockets hit a block, the first rocket to detonate will blast away the other rockets.

Rockets catch on fire when they travel through fire or lava. When a rocket travels through lava, the rocket will catch on fire until the rocket explodes. When a rocket travels through fire, the rocket will briefly catch, but will extinguish quickly. If a firework travels through water after lava, it remains on fire. Fireworks can be placed and explode over the 256 block height limit. Firework rockets can also travel through nether portals if fired inside a nether portal, they will stay at the top of the portal unable to go higher then go through the portal. Rockets can build up in the nether and all explode at the same time when you enter the nether. A rocket will not be visible under a cloud when it explodes.

Crafting
Fireworks are the one of two items in the game (the other being the Command Block) that cannot be taken directly out of a creative inventory.

Duration
When the item is hovered over in the inventory it displays the flight duration (e.g. "Flight Duration: 1").

Rough distance (in blocks) that the rocket travels depending on the flight duration.
 * 1 gunpowder: 12-21 blocks
 * 2 gunpowder: 23-38 blocks
 * 3 gunpowder: 40-57 blocks with a few exploding at 35 and 36 blocks.

Results obtained by 576 fireworks per type being set off. Using small balled and red firework stars.

Shape effects
A firework can only have one shape effect for each firework star used in the recipe. A combination of firework stars can be used on the same firework rocket when crafting.

Additional effects
In addition to the shape effects, you may add either or both of these additional effects.(Place one or both of them anywhere during the making of the Firework Star.)

Bugs

 * If a rocket explodes very close to water and/or ice, all of the nearby water and/or ice may appear invisible for a fraction of a second.
 * If a rocket explodes near a Nether portal, the portal blocks may turn invisible for a fraction of a second.
 * The small ball firework star very rarely does not work.
 * Launching rockets in flowing water may cause Minecraft to slow down and freeze, even after the rockets have all finished exploding.
 * If a rocket is placed on the side of a wall of blocks, the rocket often becomes stuck in or on the side of the block.
 * A burning rocket entity can remain underwater without the fire being extinguished.
 * In SMP, if you launch a firework with no firework star, a Java exception kills your connection and will occur every time you try to log back in.
 * When launching empty fireworks, this will prompt 'End of Stream' on multiplayer unless it has been named on an anvil. It will have no effect on singleplayer.

Trivia

 * Unlike torches and other items, if a rocket is placed in a water or lava block, it does not remove the block.
 * Rockets are not destroyed by any object, including lava, explosions, or even the Ender dragon.
 * Rocket explosions can be heard on the title screen if launched quickly before you save and quit.
 * Rockets that explode underwater look the exact same as those that explode above water.
 * Flowing water can be used very effectively to angle rockets.
 * Even though rockets have an explosion, it does not affect items, mobs, or destroy blocks.
 * Rockets cannot cause TNT or Ender crystals to explode.
 * When placed in a Nether portal, rockets quickly teleport to the Nether, where they will not explode until you enter the Nether. If you send enough rockets with firework stars through the portal, a massive colorful explosion will wait for you on the other side. This does not work in the reverse way; the rockets explode soon after reaching the Overworld.
 * Even if knocked into a horizontal trajectory by an explosion, rockets always point straight upward.
 * Rockets can be placed above the height limit of the map.
 * Rockets can be launched from a Dispenser, however will only launch upwards from the block directly in front of the dispenser.
 * The crackling sound of a firework is the same as the sounds you hear as the Ender Dragon is killed.
 * Shooting a rocket into a cobweb causes it to slow down as expected, the explosion particles are slowed down too, creating a colorful ball inside the web.