How to make a Nether portal without diamonds

To make a Nether portal without diamonds, don’t mine obsidian at all: cast it where the frame goes. Pour lava into a mold of ordinary blocks, let water flow onto it, and each lava source turns into obsidian in place. Ten cast blocks make the smallest frame; flint and steel lights it. Below is why it works, a step-by-step build, the ruined-portal shortcut, and how an AI did it the slow way.

All game facts in this post are for Java Edition 1.21.x unless a line says Bedrock.

Why you can skip the diamond pickaxe

Obsidian only drops when you break it with a diamond or netherite pickaxe. With any other tool it takes longer to break and drops nothing ^[1]. That’s the whole reason guides send you after diamonds first.

But a portal doesn’t care where its obsidian came from. The frame can be mined obsidian, a completed ruined portal, or obsidian cast in place with lava and water ^[2]. If the blocks are already standing in the right shape, you never need to pick them up, so you never need the pickaxe.

How many obsidian for a Nether portal?

The frame is a vertical rectangle, from 4×5 blocks (outside measure) up to 23×23, and the four corners aren’t needed ^[2]. The smallest portal is 4 wide and 5 tall: 14 edge blocks, 10 of them without the corners. So you need 10 obsidian, which means 10 lava source blocks, one per frame block.

The corners can be anything, or nothing. Many players fill them with cobblestone so the frame looks finished.

How to make obsidian with lava and water

Water and lava react in three ways, and only one gives obsidian [@mcwiki-fluid, sec. “Mixing”]:

So the lava has to sit still as a source block when the water reaches it. A lava source is what a lava bucket places, and the only way to carry lava is a bucket filled from a source block ^{[3, 4]}. Pour lava, let it settle, then bring the water to it, never the other way round.

Two more facts shape the build:

• Lava is slow on the surface. In the Overworld it flows 3 blocks from a source, one block every 30 game ticks (1.5 seconds); in the Nether it flows farther and faster ^[3]. You have time to place water before it runs off.
• Water doesn’t work in the Nether. Poured from a bucket there, it vanishes at once ^[5]. Cast your portal in the Overworld.

What you need

• Two buckets (3 iron ingots each) [@mcwiki-bucket, sec. “Crafting”]: one for water, one for lava. Empty buckets stack to 16 ^[4], so a few more make the lava trips shorter.
• Lava: a surface lava pool or a cave lake. Each frame block takes one bucket of lava.
• Mold blocks: a stack of cobblestone or dirt. Lava sets fire to flammable blocks around it, so keep wood away from the build ^[3].
• Flint and steel: one flint and one iron ingot, 64 uses in Java ^[6]. A fire charge works too ^[7], but it needs blaze powder, which you won’t have before the Nether.

That’s 7 iron for two buckets and the flint and steel. Compare: the diamond route needs an iron pickaxe to mine diamond ore, three diamonds for the diamond pickaxe ^[8], and the trip deep enough to find them.

Step by step: cast a portal frame

Build the frame one piece at a time, so a mistake costs one block, not ten.

1. Pick a flat spot next to your lava and clear a 6×7 area so you have room for the mold around the frame.
2. The bottom row. Dig a trench 2 blocks long where the bottom of the frame goes (the two middle blocks; the corners are optional). Line it with cobblestone on all sides so lava can’t escape. Pour lava into each block of the trench.
3. Cool it. Place water one block above and to the side of the lava so it flows over the top of the sources, then pick the water back up straight away. Both lava blocks turn to obsidian ^[9].
4. The sides. Build each side column of 3 blocks from the bottom up, inside a cobblestone mold one block wider on each side. Pour one lava block, cool it with water from above, pick the water up, and repeat one level higher.
5. The top row. Stand on a scaffold of cobblestone and do the same for the two top blocks.
6. Clear the mold. Break the cobblestone inside the frame and around it. The obsidian stays.
7. Light it. Use flint and steel on the inside face of the bottom obsidian. The fire must be the last thing you place: a fire lit in an unfinished frame doesn’t open the portal when the frame is completed later ^[2].

The quick version at a lava pool

The wiki’s portal tutorial gives a shortcut: build at the edge of a lava pool, use the pool’s own lava for the bottom of the frame, and cool it with water flowing in from the side ^[10]. You need a water bucket, at least 6 blocks and something to light it. It’s faster, but the lava under and around the frame stays, so watch your step.

The ruined-portal shortcut

A ruined portal is a broken portal frame that generates in the world, often with lava and a chest next to it ^[10]. They generate in every Overworld and Nether biome except the deep dark, one per 400-block square of a grid with 240 blocks of space between squares ^[11].

Why one is worth a detour:

• The chest. Each of obsidian (1–2), flint and steel, and fire charge has a 46.4% chance per chest ^{[1, 11]}. In Java, terrain such as lava can replace the chest; in Bedrock there’s always one ^[11].
• The frame. Normal designs hold 11 to 17 obsidian, giant ones 25 to 31 ^[11]. Most are incomplete, so you add the missing blocks.
• The lava. Many designs come with lava already placed ^[11], which is your source for casting the missing blocks.

The catch is crying obsidian. Each obsidian block in a ruined portal has a 15% chance (20% on Bedrock) to generate as crying obsidian instead ^[11], and a portal won’t light with crying obsidian in its frame ^[11]. Without a diamond pickaxe you can’t remove it, so build your frame beside the bad block instead. Adjacent portals can share obsidian ^[2], so a good side of the ruin can still be one side of yours.

Getting home again

You only have to cast one portal. When you step through, the game looks for a portal near the matching coordinates on the other side and builds a new 4×5 obsidian portal if there isn’t one ^{[2, 10]}. That generated portal brings you back to yours.

Two warnings before you go:

• Mark your Overworld portal. Monsters can wander through an unguarded portal and wait on the other side ^[10].
• The new portal can spawn somewhere awkward: by lava, at a drop or inside rock ^[10]. Step out carefully. Our Nether survival guide covers the lava edges.

Nixi’s angle: the diamond route, from her logs

Nixi is an AI that plays Minecraft by itself, live on Twitch. Her speedrun route does not cast portals. Its “portal” phase says, in her route file, to pour water on lava and mine ten obsidian, after a “diamonds” phase whose note reads “obsidian needs a diamond pickaxe”.

What that cost her in run 1 (2026-09-27, from her run-1 fact sheet and speedrun devlog):

• Diamonds at 0:56:34 on the run clock, the obsidian advancement at 2:37:15. That’s 1 hour 40 minutes 41 seconds between the pickaxe’s diamonds and her first obsidian.
• A walk in circles. She went back to the same sealed lava pocket 13 times. Lava that water can’t reach is useless, and her planner didn’t know that yet. The fix: only lava water can be poured on counts.
• A slow pickaxe. For 93 blocks, a data-file error for 1.21.4 made her bot time obsidian at 75 seconds instead of about 9.4 with a diamond pickaxe, the figure the wiki gives ^[1]. Patched the same day.
• The lab version. With items given to her in a test world (not a run result), one water pour turned a 5×5 lava pool into 25 obsidian, she mined 10 at about 9 seconds each, and the frame lit.

Would casting have been faster? Her logs can’t say, because she never tried it in a run. The trade-off is clear from the rules, though: casting saves the diamond trip but needs ten careful pours, each one a chance to make cobblestone instead. If she adds a cast-in-place skill, this post gets the lab numbers.

Next on the route: how to find a Nether fortress fast, then blaze rods. The whole run is in the speedrun route explained.

FAQ

Can you make a Nether portal without a diamond pickaxe?

Yes. Cast the obsidian in place with lava and water, or complete a ruined portal ^[2]. You only need a diamond pickaxe to pick obsidian up and move it ^[1].

How many obsidian do you need for a Nether portal?

Ten for the smallest frame, 4×5 without its corners. With corners it’s 14 ^[2].

Why did my lava turn into cobblestone instead of obsidian?

The lava was still flowing when the water touched it. Only a lava source block becomes obsidian; flowing lava gives cobblestone, and lava falling into water gives stone ^[9].

Why won’t my ruined portal light?

Check for crying obsidian. A portal with crying obsidian in its frame can’t be activated ^[11]. Also check that the frame is a closed rectangle at least 4×5 and that the fire is placed last ^[2].

Can you make obsidian in the Nether?

Not with a water bucket: water placed from a bucket vanishes in the Nether ^[5]. Build your portal in the Overworld; the game makes the Nether side for you.