You should try setting up an obsidian farm!
It requires at least one bucket, but will go faster the more buckets you have.
Consider the following picture:
Surround a 1x7 trough with some safe blocks.
It doesn't matter what it's made of, as long as the blocks won't burn away (so avoid wood, cloth, etc).
This is the object outlined in green below.
Now you should have a 1x7 depression -- you want to put lava blocks into this.
Be careful when emptying your lavabuckets, because if you try to place a lava source block on top of another lava source block you'll empty your bucket, losing the lava.
I didn't have lava accessible, so for the picture I used cloth .
It is outlined in Red.
After you've got your seven lava blocks, simply place a water block on the rim of trough, indicated by the light blue outlined wood block in the picture.
The water will flow over each of the seven lava blocks, turning them into obsidian.
This is known colloquially as "obsidian farming".
gaming.stackexchange.com/users/336/Raven Dreamer
There are a bunch of strategies, but since any way to get obsidian requires lava, first and foremost you're going to have to be careful .
Always carry around a bucket of water with you.
Remember that you can place the water on the ground, wait for it to spread, and then collect the source block back up.
Use this to turn lava into obsidian before getting to near it.
You are much better off turning lava into obsidian and mining it in place than trying to move the lava somewhere else and changing it into obsidian there.
Remember that lava produces light, so while it may protect you from spawning mobs, when it changes to obsidian it won't.
Light
the area with torches before changing the lava to obsidian.
If you're feeling really brave, you can always make a portal to the nether and collect lava there to bring back with you, if you run out of lava in the real world.
Sometimes the lava is really hard to get to safely.
If you don't feel comfortable trying to maneuver your way around, it is perfectly fine to abandon that lava spring in favor of a more accessible one.
It is always easier to find lava in a cave system than try to mine it out of a pocket surrounded by stone.
Just make sure you mark lava somehow (signs work well) so that you don't accidentally dig there in the future and get yourself killed.
When a lava spring is multiple blocks deep, it can be hard to mine the obsidian because the block may fall into the lava directly below it.
Make sure you never mine directly below yourself, and don't go diving after the obsidian hoping to catch it before it falls into the lava.
These can be especially tricky to mine.
Change additional lava to obsidian as it is revealed to minimize risk.
Most importantly, just remember the main mantra: be careful.
gaming.stackexchange.com/users/1719/Invader Skoodge
I generally agree with StrixVaria except for one point.
Given how long it takes to mine a block of obsidian and the fact that you need diamonds first, it can be just as quick and easy to move the lava in a bucket where you want the obsidian to be and cast the obsidian there.
This way there is practically no threat of falling into the lava or "losing" obsidian to deep lava pools.
Of course if there is no lava near your project, mining the obsidian at the source might be a better option.
gaming.stackexchange.com/users/304/JavadocMD
Guys you're all wrong.
Find a big pool of lava and turn it into obsidian.
Mine one and let it get destroyed, then dump water in the hole where it was.
Face in one direction and hold down your mouse button.
As you mine a block, it is nearly destroyed but the water flows in first, saving the block and making the lava beneath obsidian so you can walk on it.
Go 7 blocks then go back to the start and go in a different direction, always in the water flow.
It is definitely the easiest way
gaming.stackexchange.com/users/None/
Bring two buckets of water.
Dig a one block deep 2x2 pit in the ground and place water in the top left and bottom right squares.
You can draw unlimited water from this pool, so fill both buckets again.
Keep them both on your bar for safety.
Pour water onto the rock next to the lava pool, turning the top layer into obsidian.
Take care not to be swept into the lava by the water.
Take the water back.
Dig a ditch around your new obsidian block, one block thick and one block deep.
Be careful as there may be a second layer of lava below the obsidian or behind an adjacent wall.
Stand in the ditch as close as possible to the obsidian block and mine it with your diamond pick.
Standing here guarantees that you'll pick up the obsidian block.
It won't fall into any lava below, and neither would you (as you would if you mined from above).
Continue this method
one layer at a time until you reach the bottom of the lava lake.
Remember to pour the water onto rock so that it flows onto the lava lake, rather than into the lava, as that will create only one obsidian block and expend your water.
Take extreme care.
If you open a lava flow by accident, cover it with cobblestone or pour water.
Leave your diamond pick in a chest when exploring lava lakes and only bring it with you when mining obsidian.
Always carry two buckets of water in your bar, two cooked pork in your bar, and at least two more cooked pork in your inventory.
Try to place 2x2 water pools a safe distance from where you mine.
Don't stand diagonally adjacent to lava, or you can catch fire.
gaming.stackexchange.com/users/3454/Joe Dovahkiin
Press F4 and mine the portal .
(in Alpha)
gaming.stackexchange.com/users/3229/Nakilon
Mining nether portals.
Build a nether portal without the corners, go through it, and it will have the corners on the other side.
Mine them, go back through, and repeat.
gaming.stackexchange.com/users/88613/evandentremont
In single player Survival mode in Minecraft Alpha, what is the safest way to create an obsidian farm? I've come across naturally occurring in obsidian in Survival MP, but that was easy to mine because there's no damage, so I could safely hack away while I was on fire. I'm kind of paranoid about working with lava in single player though.  What will I need to do this? How can I do it without being reduced to a digital pile of ashes and tears?
What's the safest way to farm obsidian without burning to death?
gaming.stackexchange.com
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gaming.stackexchange.com/questions/10465
gaming.stackexchange.com/users/160/FAE
Find a big pool of lava and turn it into obsidian. There are a number of ways to do this, all of which require care. You can set up an obsidian farm or turn an entire pool of lava into obsidian.
Users suggest care in this operation, however an obsidian farm is the most upvoted reply, and a pool of lava turning into obsidian is also suggested. 