There are plenty of Instructables and other how-to's on making Thermite, the incendiary mixture that can not only raise, but also burn, eyebrows. (The concept for this Instructable came from 'the Anarchists Cookbook', and since it doesn't give many's how I do it.) Now, there's nothing wrong with powdered forms of Thermite, that's how I got started a few years back, but sometimes you just want something rock solid that burns nice and bright/hot.

That's where Cast Thermite comes in. And the best part is, If you have some thermite on hand already, it's pretty easy to make! If you don't, never fear, for I will be starting at the beginning with nothing but the raw materials.
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Step 1: Obtain the Materials

So you made it through the intro? Good. There's something that must be said before we go any further. I'm not liable. For anything. Do your homework and be sure you know what safety precautions to take when handling something like thermite, such as not looking at it during ignition since it gives off harmful ultraviolet light! Be smart, treat this stuff with the respect it deserves. It's not flash powder but it's certainly not sugar either. ;-)

Now that that's out of the way, onto the fun part. The preparations!

The first thing to do is understand what thermite is made up of. Most commonly, homemade thermite is made up of iron oxide (rust) and granule or powered aluminum. When mixed together, these two metals create an incendiary capable of reaching temperatures of several thousand degrees. For more info check thermite's Wiki page. So:

What we need:

  • Fine (0000) Steel Wool (not pictured)
  • Aluminum
  • Some kind of scale
  • Plaster of Paris
  • Handling materials (spoon, cup, paper, coffee can...)
  • Some kind of mold to cast your thermite in
While I'm at it, I'll explain the best way to get a hold of the materials.

  • Steel Wool
Off to the hardware store! Honestly though, I buy my steel wool at Walmart unless I can find bulk fine grade steel wool at our nearby Harbor Freight .

  • Aluminum
Well, you could always go online and purchase some high grade Aluminum powder like I did. Before I thought to do that, I just ground strips of aluminum foil in a cheap coffee grinder. IMHO, the larger grains made from the coffee grinder method make for brighter and more enjoyable light shows.

  • Scale/Plaster of Paris
Ever heard of Michaels? It's a nice little place a lot like Hobby Lobby. Plaster of Paris and the scale can be bought at either of these places, and probably at Walmart as well.

  • The Mold
Use anything you want to, whatever suits your fancy. I use a small ice cube tray. Film canisters would probably work fairly well, as would larger tupperware containers for really big batches. Whatever floats your boat.

Finally, you say. I've got everything you told me to get. Let's get started!

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spork30006 days ago

How did this appear in my email feed? I know I'm a fan of thermite, but this is 6-ish years old... and doesn't appear that active currently. So, why feature it in an email blast?

Unless doing thermite demos is a good halloween treat (umm, really? really?) then this seems a bit inappropriate to me.

johnnycharr10 months ago
I wonder if a mixture of potassium permanganate and glycerine would ignite it, if you could figure out how to mix them from a distance on the thermite that is.

That's how I light my thermite. The reaction is delayed by several seconds, so you have time to move to safety.

Hi guys i have a question about this iron oxide i understand its rust but all the videos i've watched about making iron oxide its a liquid with a battry charger and old nail etc. Im sure youve seen them but if i were to scrape rust off let's say an old bike then used a ball mill,mortar pestal,etc would that still be iron oxide or something else? thanks

jcwelsh20008 months ago

Use old prescription, film canisters filled 2/3 then you could thread fuse thru the cap and into the mix before dry... Just a thought.

Hi Zlwilly & The Instructables Community,

Just a thought on possibly problamatic ignition.

I have heard of people using sparklers to ignite the powdered mixture, but obviously this cannot work here.

So I got thinking, why be constrained by this?

I thought that while the mixture is setting why no put a short cut length of drinking straw into the top of the mixture (possibly plugged to stop water equalisation). Once set you then have a convienent hole to place either a short length or a full sparkler for a timed fuse.

Just a thought as I said, but I would love to hear if someone gave it a go!


The Apple Sauce Man

Victor Lam4 years ago
is it possible to use the pre-ground aluminum oxide used for sand blasting?
No it is not possible. Aluminum oxide is not aluminum. To answer your question more thoroughly remember that thermite releases heat by striping the oxygen off of the iron and 'burning' the aluminum. If your aluminum is pre-oxidized this reaction cannot occur.
Aluminum metal (Even in alloy) forms an oxide layer almost instantly after having the existing oxide layer removed and then being exposed to oxygen. I don't remember the exact time, but its on the order of nanoseconds.
shouldn't the iron oxide be reddish brown?
Fe(III) Oxide is usually a brighter "brick" red
qwerty9241 year ago
i forget the name of it but there's a type of radiator repair stuff that contains powdered aluminum and you can also obtain it from an etch-a-sketch
brainscan1 year ago
Hey not sure if anyone else has mentioned this but you'll have an easier time mixing if you add the powder to the water. It will also give you a few extra minutes of play time before it starts to set. Once it's mixed add a pinch of table salt and it will halve the setting time. This only works with plaster of Paris, with harder plasters like dental ones it slows the reaction. Don't ask me why I don't know. Not sure if the salt would affect the burn though.
rnorman32 years ago
would a rock tumbler work as well?
Johnhall441 year ago
I think I have an experiment to do using arrows =D
a better way to get iron oxide is by the electrolosis of a salt water solution with some iron rods. Not graphite. Then filter the muck and let it dry. Grind it up in a pestle and mortar and there powdered iron oxide.
That is a 'better' way to get iron oxide, if you're looking for efficiency from cost/time/end-product mass Vs. beginning mass. There is one thing that you did not consider, though, and that is the fact that when you make iron oxide via electrolysis you do not have an end product of Fe2O3 which is the best iron oxide to use for thermite mixtures.
Whats wrong with Fe3O4? it has more oxygen, shouldn't that let the thermite burn better?
I dont believe you can make Fe3O4
i  didnt think that you could make h2o2 but i was worng...
Peter5465 hg3412 years ago
Can someone help me out here?

I did through water electrolysis. When you get to the drying part, evaporate it as heating it(in a propane grill) turns most of it back into Fe2O3.

(pic: red is the grilled, black is evaporated)
oh kk nvm
nice icon
reedz6 years ago
It would be awesome if you could freeze an ignitor into it, like a press button that when you throw burns.
Peter5465 reedz2 years ago
Can someone help me out here?

dlmetcalf2 years ago
Thanks for the Instructable. I'm going to second another commenter and recommend 2% Dextrin as the binder instead of plaster (bake cornstarch a.k.a. cornflour in the oven for 2 hours at 200C, mixing every 30 mins). Lighting it with KMnO4 and glycerol is generally much safer than a propane torch or flash powder mix too (at least gives some delay). As a word of caution, making thermite is probably classed an manufacturing pyrotechnics and illegal in most places. Unless you have experience with pyrotechnics, safety practices, solid chemistry knowledge, etc. don't mess with it. Also if you add chlorate (as one poster suggested), make sure you don't use First Fire Mix as it contains sulfur which can degrade to trace amounts of sulfuric acid and cause spontaneous combustion.
Forgot to add that when the block is x'ed out with 1/4" deep grooves just sand it flush and go again. Also check your alloy, just because it's Al doesn't mean it's pure.
I like to place my iron oxide in a small coffee can with some old BB's and ball bearings and give it a good shake for a few minutes. As for the aluminum I have a 6x6 block from a local hardware store that I cut grooves into with a hacksaw. Light pressure will get close to a fine powder.
SirStokes3 years ago
Where in the anarchist's cookbook does it talk about thermite?
ilpug SirStokes2 years ago
The part that also says that that isn't something that should be involved with this site.
Would it be possible to simply just stick a 10 cm or so length of magnesium ribbon in each cube while they're setting?
built in fuse: I like it!
The best way I found to do this is using a metal pipe about 4 or 5 in. wide and how ever long you want I'd keep it around 3 feet long. Stuffing the pipe with steel wool, lighting it (duh), and having a fan blow through the pipe from one end. it works great. ;)
mrmerino2 years ago
You can also light the steel wool with a 9V battery.
i need to grind up aluminum is there another way besides a coffee grinder
Small rock tumbler with BB's works great for pieces of Aluminum Foil.
aluminum seems to be a problem for a lot of people i have found that the best quality of aluminum powder can be found inside of an Etch-a-Sketch. the grey powder in side of it is as fine a powder as it comes you can even use the beads to give a good combination of coolness and functionality!
...again, a rock tumbler with BB and pieces of Aluminum Foil WORKS AWESOME. In my opinion buying or even salvaging an etch-a-sketch for the aluminum powder is:

a) More work than it's worth.
b) Waste of an etch-a-sketch (they're not hard to fix)
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