Fun With Bismuth

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About: I run Neal's CNC in Hayward, CA, an expert CNC cutting and fabrication service. Check out what we do at http://www.nealscnc.com/. I'm a founding member of Noisebridge, a hackerspace in San Francisco, and Ac...

Bismuth is a lesser-known metal. It isn't seen in consumer products much (it has some applications in manufacturing) and isn't particularly rare or valuable. A good overview of bismuth is here.

It has several qualities that make it suitable for amateur experimenters: it's not poisonous, it has a fairly low melting point, it's cheap, and it has a really lovely crystalline structure. It's great fun to play with.

I got the health question a lot from people I mentioned this project to. Unlike lead, mercury, nickel, or other metals, there is no significant health risk from vapors or from touching bismuth or ingesting small amounts (it's actually the active ingredient in a popular brand of stomach medicine). There is of course a burn risk when you melt it, but adequate precautions and basic care reduce this to levels that are quite acceptable for me - it's really no riskier than boiling a large pot of water.

Step 1: Equipment and Safety

Bismuth's melting point is 520 F, 271 C. This can easily be achieved on a stovetop or, as I did, with a camping stove. It will coat the interior of your crucible so don't use something you cook with often.

As with nearly anything these days, bismuth can be purchased on the Internet. I got a pound for about $15 US. This turned out to be a cube (more or less) of an inch and a half to two inches on each side.

Obtain the following additional items:

  • goggles in case of splashing
  • leather gloves
  • crucible - stainless steel pot or bowl
  • heat source - stovetop works fine, i used a camping stove
  • big tweezers to pick out crystals
  • pliers to handle crucible if it has no handle

The crucible I used (OK it's a mixing bowl from IKEA) is a little big for the pound of bismuth I got. Because melted bismuth oxidizes so fast, you want as small an area as possible exposed to the air. Also it would have been slightly easier to handle on my camp stove.

I got my bismuth from Rotometals for $15 plus about $7.50 shipping, which was lowest for my location. Other online sources sell it as well.

Step 2: Melting

This is very straightforward. Turn on the heat and wait. Full melt took about 12 or 15 minutes at whatever temperature I was getting from the camp stove.

Step 3: Crystals

Once the bismuth is all melted, turn off the heat and let it cool down. As the metal cools, it will create crystals under the surface. Poke it gently with the tweezers and you'll see where solid pieces have started to form. Gently pick these up and turn them over to see the crystalline structure underneath. Not all pieces will form the beautiful step-wise cubic crystals, but you can remelt any that you don't want to keep.

The iridescent colors are caused by oxidation, which happens very quickly when the melted bismuth is exposed to air. It may be possible to reduce this by plunging the crystal immediately into water, but I did not think to try this - next time!

Step 4: Pouring Into Water

What would melted bismuth do when water cooled? There is only one way to find out! We set up a little screen for me just in case there was a lot of splashback, but this turned out to be unnecessary. Here's a video:


The picture shows the results. Notice there is no oxidation!

Step 5: Pouring Into Molds

Here at Instructables HQ we have lots of weird stuff lying around. We found an old silicone mold from last Valentine's Day and poured the melted bismuth into it. The results were not astoundingly great visually, but the process was excellent and the cast bismuth hearts are satisfyingly heavy in the hand. With some experimentation a better cast could surely be produced.



We also poured some and attempted to insert pins to make pushpins. This did not work so well - the plastic one melted and the nail is loose. It was moved slightly before the bismuth was quite solidified -- and the bismuth doesn't stick to steel.

Step 6: What Else?

I remelted the pieces five or six times. After a while there was a crust on the top of the melted metal that didn't seem to want to flow back under. It's not crystalline and it wouldn't melt. I suspect this was just some that got particularly heavily oxidized after all the melting and solidifying.

I sanded the back of one of the crystals that was particularly beautiful. I will epoxy a loop onto it so it can be worn as a pendant. What with the non-stickiness of the bismuth I'm not sure epoxy will bond to it but I'll update this when I find out.

One thing I noticed was that the bismuth did not bond to things very strongly. It got all over the ends of the tweezers but I was able to crack most of it off once it had cooled down. It splattered a bit over our metal table but didn't stick to that either. It didn't stick to the silicone mold at all (of course this is also a property of silicone). It didn't stick to the nail. I was able to crack some of it out of the mixing bowl, although not all. The bismuth particles on the sandpaper fell right off too, unlike most things which tend to stick to the grit, and can only sometimes be brushed or tapped off.

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    168 Discussions

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    Jimmy-leeS

    2 years ago

    What will happen when mixed with gallium?

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    wenw

    2 years ago

    do u think that soap stone can be used as the mould?

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    JoshA11

    3 years ago on Introduction

    This project was pretty cool. I made my bismuth crystals from bismuth bought here:

    http://www.ebay.com/itm/100-grams-Bismuth-Metal-99-99-Pure-Element-Crystals-Ingot-Chunk-USA-/251976590733?pt=LH_DefaultDomain_0&hash=item3aaaf9a58d

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    Just because bismuth subsalicylate is in Pepto-Bismol does not mean Pepto-Bismol is toxic. Think of oxygen.. It's two oxygen atoms joined together by a double bond. It's safe as we all know. Add another oxygen to the mix and you O3 which is a poisonous gas called ozone which is a deadly oxidizer and will eat away at the mucous membranes of your lungs.

    Did you think something as minuscule as an extra oxygen atom to O2 could be so deadly? The same applies to medications. If you only knew what chemicals are used in the manufacture of many of the drugs we all consume on a daily basis..

    The point I making is that while this is a heavy metal, the anti-acid Pepto Bismol is safe to consume.

    I have to wonder, if someone went about bismuth crystal production from a chemist's perspective could you possibly use a stir bar on top of a hot plate in a aluminum pot at the moment where the temperature is ripe for crystal formation to yield a winding staircase effect?

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    WesChandler

    4 years ago on Step 3

    I would advise against putting molten bismuth in water. I've done it. It exploded and I ended up with bits of molten bismuth all over me (thankfully not on my face). Needless to say, it was extremely painful. I later realized this happened because, like water, bismuth expands when it solidifies. When I put molten bismuth in water, the outside solidified before the inside and a moment later it went everywhere.
    But, this is a really good idea for making crystalline. I'm definitely going to try it. Thanks!

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    techchimp

    4 years ago on Introduction

    First off, love the topic and good instructable!

    Second, a word or two about safety...

    Bismuth metal is "safe" to use if you can guarantee its source. If you are unsure of the composition, you should take vapour and handling precautions (gloves and masks).

    Some alloys of bismuth contain cadmium, lead or other toxic compounds.


    You can always spray a clear-coat on your finished crystal if you are concerned about handling the metal.

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    craftyv

    4 years ago

    The melted Bismuth needs pouring into another warmed pot holding back the grey "slag" so it doesn't go with the Bismuth. Then let the Bismuth cool as slowly as possible because this is how the crystals are formed. This will give much better results. Good luck.

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    draghi

    8 years ago on Step 1

    The link you posted is good... except to get shipped to Australia it costs $92.23 for one pound of the stuff.

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    cathyjblakedraghi

    Reply 6 years ago on Introduction

    You need to have someone ship it to you in a USPS International Flat Rate box, it's only $17 for a small box to Australia.

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    coolo52

    6 years ago on Introduction

    i love how you said that the melting bismuth reminded you of the wicked witch of the west.

    Looking at the first photo, it's kind of amazing that nature would create something like that. Beautiful and mesmerizing are the terms that come to mind...

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    8v92

    6 years ago on Introduction

    What makes an element toxic or not is more than just its atomic number for example chlorine is very toxic but has a much lower number than gold that is for all porposes non toxic. What make somthing toxic is its chemical activity as determined by its valance or number of electrons on the outer shell of the atom.

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    drewgrey

    7 years ago on Introduction

    Great instructable. Bismuth would be a great material...except for the name...How about Shinyium

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    arizonadixon

    7 years ago on Step 4

    this is very cool but rapidly cooling the bismuth is counterproductive for crystal formation you wold get larger and more defined crystals if you cooled the bismuth slowly, the longer the cooling the bigger the crystals

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    zack247

    7 years ago on Introduction

    bismuth--
    how soft is this metal? as i was reading the ible i was thinking about making home made die cast cars or maybe even heatsinks for computers..

    how does paint stick to it?

    and i would consider possibly a 2 part mold or something, it may help with the oxidization if all that makes contact with the air is a part that will be cut off and remelted.

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    Void Schismzack247

    Reply 7 years ago on Introduction

    For casting I think it would be cheaper to use a casting alloy such as "white metal"... unless you want the unusual properties of bismuth such as it's diamagnetic effect.
    For two part casting I recommend http://www.hirstarts.com/moldmake/moldmaking.html
    Silicone RTV is lovely stuff to work with :)

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    aliencam

    9 years ago on Step 3

    An even better way to prevent oxidation would be to do this in a non-air atmosphere. You can accomplish this by using blocks of dry ice, around the bowl, this would remove a lot of the oxygen from the atmosphere around your experiment. You would have to figure out a way to keep the dry ice above or at the level of the rim of the bowl though, as CO2 is heavier than air. This would also allow you to get crystals of bismuth that wasn't oxidized, instead of the flecks and blobs that you would get by pouring it into water. the oxidized colours are part of what makes bismuth crystals awesome though, so why would you want to prevent them?