Guide:Renewability

All Resources are Infinite
Resources only differ in their scarcity. Although the amounts of certain items appear to be finite, (i.e. the number of Ivy Chests), other resources grow back, spawn randomly or can be otherwise replenished. Generally, all items can be transferred between worlds and between characters and thus there is no incentive for saving up, rationing or hoarding items or materials. Rather, a player can choose to gather and produce materials in bulk, or collect and craft items as required, while discarding anything that is of no immediate use. At any time a new world can be created and all its treasures and minerals gathered, the character's Inventory, Safe, and Piggy Bank are shared between different worlds. Also, any item that can be bought from an NPC is infinite, as well as anything dropped by a monster, provided you have the necessary biome.

Wood
Wood is arguably the most common and renewable resource. Chopping down Forest and Hallow Trees frequently drops Acorns that can be planted to grow new trees. It can also be found growing up by itself on jungle blocks (creating an artificial jungle is a good way to harvest wood without using acorns). Trees that are in the Corruption, Crimson, Snow, and Jungle biomes also drop acorns. It is rare, yet possible, for surface Giant Glowing Mushrooms to drop an acorn.

Wood is one of the most versatile resources as well, as it is used in both construction and crafting. For a small example:
 * Wood can be used for both building structures and background walls.
 * Wood is used for creating torches and wood platforms.

Sand
Sand is an infinite resource if you have patience or the equipment:
 * Antlions can be goaded into generating more sand, albeit very slowly.
 * A Sandgun used with ammunition-conserving equipment, such as the Necro Armor set, can produce infinite sand.

By extension, Ebonsand, Crimsand and Pearlsand are also renewable, since the normal variant can be intentionally transformed prior to harvesting. Be aware that the blocks can only be infected during Hardmode.

Cactus
Cactus is an infinite resource as long as there is 1 layer of sand, since it spawns automatically. Cactus can be harvested with ease by just removing the 1 sand block below it and sold for money or crafted to potions.

Glass
Glass is indirectly renewable because it is crafted from sand, which can be produced infinitely.

Bombs
Bombs are an infinite resource since they can be created infinitely using wiring and a Bomb Statue, or can be bought from the Demolitionist.

Crafting Materials

 * Main article: Guide:Gardening

Herbs
All herbs are renewable resources because they can be replenished by seeds, or grow naturally in their respective biome.

Ores
Demonite Ore and Crimtane Ore (depending on whether your world has Corruption or Crimson) are renewable resources as they are dropped by Eye of Cthulhu, Brain of Cthulhu and Eater of Worlds.

Meteorite is spawned randomly with a small chance of "falling" each night and a much larger chance when actively smashing Shadow Orbs. Meteor Heads spawn near large concentrations of meteorite and have an approximate 1 in 50 chance of dropping a chunk of the ore when killed. It should be noted that once you enter Hardmode, meteor heads won't drop anything.

Obsidian can be produced without limit in an obsidian generator if one is willing to exploit the liquid physics bug.

All other ores (with the exception of Hellstone) are now renewable thanks to the power of Fishing for wooden crates, and can rarely be found by slimes.

Stars
Fallen Stars will frequently fall from the heavens during the night.

Gels
Gel is renewable and can be easily stockpiled by hunting slimes or simply using a grinder mechanism based on the Slime Statue.

Cursed Flames and Ichors
Renewable because they drop from Clinger/World Feeder and Ichor Sticker repsectively

Liquids
All liquids can be created infinitely, if you are willing to exploit bugs. Main article: Guide:Making liquid.

Obsidian generator
Obsidian can be harvested by creating a generator. A generator is an exploit that allows the infinite creation of lava and water, to create obsidian. Liquids in Terraria can be duplicated in this way because of a game mechanism in which a full bucket will always produce one full block of liquid, while less than a block of liquid is required to fill the bucket.

This video contains a detailed explanation on how to set up the machine. (instead of just using two blocks on the lava duplicator use three or four, this will allow you to click faster like the water duplicator. since the lava will spread out faster instead of taking a bit longer to actually fall off the block)

With the introduction of mechanisms such as Pumps, wire and timers in 1.1, it is now possible to construct an automatic obsidian generator, which does not require using buckets to repeatedly refill the lava or water vats.

A sample set-up of an automatic obsidian generator can be found here:

Video detailing the construction of a fully automated Obsidian Generator using vats and pumps.

Flooded Hellevator (strategy from LachlanInc)
Another way to make lots of obsidian without going to and from the Underworld is to make a Flooded Hellevator. This works well if you have a cave with LOADS of water pools. You can also take the ocean, though if you have computer edition you will want to save one so that you can fight Duke Fishron. If you do just start a hellevator above the water pools and start digging downwards. Eventually, as most players know, as you get closer to the Underworld you will find lava instead of water (the place with lava pits don't alter the water with you into more lava, which is a good thing). As the water collides with the lava, you will get lots of you-know-what (obsidian).

(found while making a Flooded Hellevator)

If your Flooded Hellevator collides with a HUGE lava pit (see next picture), you might as well have your own money maker!



(this screenshot was taken during a Blood Moon) If you are going to take my advice, here is what I recommend: Extra recommendations from Thirdy2:
 * Scuba Gear
 * Lucky Horseshoe
 * Cobalt/Obsidian Shield
 * Water Walking Potion/Obsidian Skin Potions. Just in case. Drink this especially if you have a habit of digging directly down.
 * Lava Charm/Lava Waders (if no other option is available, read below)
 * Not digging down on Obsidian. (No really, I have unfortunately experienced this)
 * Gills Potion (for the water).

In Hardmode:
 * Scuba gear < Neptune Shell
 * Lucky Horseshoe < Wings
 * Obsidian shield < Ankh Shield
 * Mechanism of 1 pump 2 Outlets