Introduction: Build a Furnace, Create Custom Molds, Cast a Piece of Jewelry, Then Mount a Custom Cut Stone

Picture of Build a Furnace, Create Custom Molds, Cast a Piece of Jewelry, Then Mount a Custom Cut Stone

In this instructable I show how I built a furnace - very similar to another design, just scaled down a bit. To view this project and some other pretty cool ones I haven't had time to transcribe over to instructables visit my site

I designed a piece of jewelry, made a mold using the lost wax technique, cast the piece of jewelry then set a stone in it. All the materials are easily obtainable. It works with precious metals but if your on a budget and even cheap jewelry from Wal-mart can be melted down and used. It makes an attractive piece that carries a certain homemade charm (no pun intended) without the tacky homemade look. I made a necklace, but the technique can be applied to rings, bracelets, earrings, glasses, small machine parts... really the only limit is your imagination. (although for highly complex designs with many small or detailed surface features you may need to build a centrifuge which I describe near the end)

Step 1: Gather Materials

A list of required materials

-1 Quart paint can
-10 LB bag Quickrete
-Butane torch
-1" x 7" pipe
-1/2" diameter steel pipe
-3/4" diameter copper pipe caps
-10 Ga. Steel wire
-Brick (without holes)
-Something to mix the concrete in
-Something to mix the concrete with
-Small piece of cardboard
-Masking tape
-Hand tools
-Dremel (optional)

-Faster Plaster
-Source of wax (unscented candles work well)
-Carving tools (exacto knives work well)
-Small wooden blocks
-Heat source (microwave works well)

Casting supplies
Any metal with a melting point under ~2000 Degrees F
Small fire to heat mold, camp stoves work great

Finishing Tools & Supplies
-Polishing compound
-Dremel with: Polishing Wheel, Engraving Bits (optional), Diamond Cutting Wheel (to cut stone)
-Fine sandpaper (if casting is rough)
-Claps, rings, fasteners, chains etc... (available at most craft stores such as Michaels or Hobby Lobby)
-Marine grade epoxy (to set stone)
-A box to put finished jewelry in (optional)

Step 2: Build Furnace

Picture of Build Furnace

Building the furnace is pretty straight forward. Mine is very closely related to this furnace, the only difference being that mine is smaller.

The theory behind the furnace is basically just to trap the heat from the blowtorch so that you can heat up a crucible really hot. We do this by filling a paint can with concrete but leaving a cylindrical hollowed out portion in the center. By placing your metal in a crucible sealing it in the furnace we can obtain temperatures much higher than by just heating the crucible with a blowtorch. The furnace also gives a nice even heat.

Im not going to go into great detail on the construction of the furnace because the other guide does
a fantastic job of it, however i will give a brief overview of construction and a few things that are critical to success.

1. Cut 1/2" pipe down to length. This is the channel the blowtorch goes into. Its ok it its a little bit too long, just make sure that the air holes on the blowtorch aren't blocked, otherwise you will just get a very cold, useless yellow flame. one end should be cut with about a 30 degree angle so that it lies flush with the wall of the cylinder

2. Cut a hole in the can so that your 1/2" pipe will press fit into it. Its important that the pipe enters into the very edge of your hollowed out cylinder, thereby creating a heat spiral in the chamber, which helps prevent hot spots. (The other guide describes this much better than myself)

3. Somehow suspend your 1" pipe ~3/4" centered above the base of the paint can. I used a tent stake taped to the edge of the can. You can see that I wrapped my 1" diameter pipe in cardboard and covered the ends with masking tape, this was so that concrete wouldnt get into it, and to make it easier to remove once the concrete had cured.

*important* make sure that concrete cannot get into your small channel for the blowtorch and that after pouring the concrete that the pipe goes into the hollowed out champer (not blocked by concrete) the way i did this was to cut a circle in the cardboard surrounding my pipe which the smaller pipe fit into.

4. Let it cure for at least 2 hours then put it in the oven for an hour. I removed the cylinder after an hour then put it back in for 3 more.

*important* make sure that you dont use rubber tapes to secure the inner cylinder because they will melt all over your oven and smoke and possibly catch fire. I used masking tape which browned slightly but never caught fire. I think this was because of the prodigious amounts of moisture coming off the concrete so pay VERY close attention when you are baking it. If i were to do it again i would use wire to secure everything instead of tape. The masking tape and cardboard are pretty much safe because they are sorrounded by concrete and unable to burn.

5. Immediately test fire it for 30 minutes after taking it out of the oven. Since the concrete is already hot this will help prevent stress fractures from the rapid heating of the blowtorch. This fully cures it and i used mine immediately after this step. Be warned that it could fracture any time shooting out tiny thousand degree particles of concrete so eye protection is REQUIRED.

6. Build the crucible. My crucible was pretty simple, i just drilled two 1/16" holes on opposite sides of the 3/4" copper pipe caps and bent the wire into a sort of hook shape which went into those holes, this allows the crucible to rotate when you do your 'pour'. I put a 90 degree bend in the wire crucible holder so that the brick could sit atop it.

7. Melt down stuff in your furnace just for fun.

Step 3: Make Molds

Picture of Make Molds

The molds are created using a process called lost wax casting. Basically you carve whatever it is you want to be made out of wax. You set it in plaster then melt the wax out leaving a cavity in the shape of whatever you carved. You pour molten metal into this cavity and let it cool, creating a beautiful piece of jewelry. Its a little bit easier said than done but with a little practice becomes relatively easy.

1. I bought a big candle at walmart and melted it down with my blowtorch into a plastic cup. The candle had a bit of a grainy quality to it that was gone after melting it. Which allowed me to get much more detail when carving and it prevented the wax from 'crumbling'. You can melt the wax into anything that wont melt and you dont mind getting waxy.

2. Carve. There is no real set way to do this. I traced an outline of the piece onto the wax and just free handed it with an exacto knife. The picture of the finished mold is from an earlier design for my piece, after many tries the design evolved into what you see in the first picture.

3. Set the wax in plaster. I used a special microwavable version of plaster called faster plaster that after an hour of curing can be microwaved for a few minutes fully curing it. This isn't necessary but it prevents having towait 24 hours for the plaster to cure and if you invert the mold on a couple wooden blocks (i used jenga blocks) all the wax will cleanly melt out (preferably onto a paper towel) while its in the microwave. I suspended the wax piece by a hanger in the center of the plaster and used a cut off styrofoam cup to hold the plaster. After an hour the plaster is hard enough to remove the hanger and peel off the cup.

Also make do your best to remove any air bubbles from the plaster. Tapping it gently on a table helps remove some, i mixed my plaster using a gillete vibrating razor modified so that it didn't have any blades (basically just a vibrating handle) it worked very well.

*important* you cannot leave the styrofoam cup on the plaster while microwaving because it prevents the water vapor from escaping from the plaster.

4. Admire your awesome mold

Step 4: Casting

Picture of Casting

1. Setup - you want your mold hot and ready to accept the metal, it needs to be hot so it doesn't fracture when receiving the ultra hot metal. It also keeps the metal hot longer thereby flowing better which in turn gives your piece more detail. I used a camp stove which produced a ring of fire almost perfectly the diameter of the mold. You could build a fire if you were outside or possibly heat it up with another blowtorch if you had one (you cant use the one for your furnace)

2. Let the furnace heat up for a few minutes, make sure you have the brick on top to keep the heat from escaping. You want the crucible in the furnace.

3. Put your metal in the crucible and lower it into the furnace. Replace the brick.

4. After waiting a few minutes take the brick off and check the metal, if its red hot and molten then its ok to pour.

5. Quickly but carefully pull it out using pliers on the edge of the wire crucible holder. Bring it over to the mold and pour.

6. Slowly remove heat from the mold and let it cool for at least an hour before touching.

7. You could possibly pop the metal casting out of the mold but i found it easier just to break the mold.

8. Inspect your piece, if it didnt work the way you wanted try to figure out why not (was there air bubbles etc...) and try again. I had to do at least 10 castings before i got the results I wanted. (although i didnt have a sweet guide like this to follow)

9. Next step finishing!

Step 5: Finishing

Picture of Finishing

The piece came out with a bit of a rough texture which i had to polish off. The back was also entirely too thick so I ground it off using a sanding wheel on my dremel.

These steps vary greatly depending on what it is you cast but what i did was

1. Grind down the back of the piece so it was flat
2. Polish the front to a nice shine. I used automotive polishing compound and a polishing wheel on my dremel
3. I used an engraving bit to engrave the initials of the recipient into the top.
4. I used a diamond tipped cutting bit to make the recess for the stone
5. I cut the large turquoise stone (which i had obtained from another piece of jewelry) down to size then polished that using automotive polishing compound as well. Lots of tiny adjustments to the stone later it was a perfect fit.

Step 6: Mount Stone and Add Chain

Picture of Mount Stone and Add Chain

I mounted the stone using a clear drying marine grade epoxy. Its relatively straight forward. Its a two part epoxy so i mixed it. Applied it to the recess in my piece then put the stone in. I let it cure overnight then gave the piece a final polish so the edge of the stone was perfectly flush with the metal.

To mount the chain i bought a pack of sterling silver rings from Michaels for just a couple bucks. Just put the ring through the hole in the piece then solder using silver solder from radio shack (i know its really low silver content but it doesn't contain lead which is important.

Step 7: Closing Remarks

This a great way to make a very special gift. But it really can be used to make anything small and metal, the only limit is your imagination.

Depending on the metal that is being used the amount of detail obtainable varies. For example I was unable to obtain very sharp, clean edges, they always came out with a slight fillet. At a certain point you may need a centrifuge to force the metal where you need it to go. I'm currently working on a design for a home made centrifuge and will post the design on here when it is complete. In the meantime has an article on lost wax casting which explains the use of a centrifuge

Make sure you dont make jewelry out of lead. It is toxic. And tacky. And really heavy. But mainly toxic.


curvy77 (author)2012-09-28

is it possible to place the stone in the mold (loosly) than pore the metal on top, so that the metal forms around the stone? this will eliminate the need for the epoxy.

ZachariahH1 (author)curvy772015-07-21

There are cast-in-place stones that allow this. Look up a PMC (precious metal clay) website and take a look at the stones they typically sell along with their other products.

EricaH4 (author)2015-02-24

I stopped reading at "tacky homemade look".

SpanielS1 (author)2014-12-18

although i am sure this works pretty well, using a portland-type concrete (quikcrete) is pretty dangerous for applications with high heat. the concrete contains air pockets and water after it hardens, which can cause it to burst/explode. this can cause SIGNIFICANT INJURY. This should be constructed using REFRACTORY CEMENT (quikcrete does make a fireplace mortar, although I would be looking at cements carried alongside kiln supplies which are good above 2000 degrees F).

jeddar (author)2014-12-10

As a question, I notice you list a butane torch in your list, but the picture shows a propane.. Does this re4ally matter? I ask since I'm not sure if the two fuels generate different temperatures.

dima.averin (author)2014-08-05


How are you?

I need to make a metal mold. It's supposed to be in the form of a diamond 1-2 inch and empty inside.

I need to be able to put liquid plastic into the mold, cool it down and then somehow easily get the finished product out of mold.

So I'm wondering if you can make it for me and how much is it gonna be?


sdfgeoff (author)2012-10-07
Just a note, you may want to change your site title from 'Untitled Document' to something a little better.
In the head tag of the page add:

<title>What you want the title to be</title>.

robrt maccian (author)2012-07-27

will it cast aluminum alloy such as t-6 for casting lower recievers for ar 15 assault rifle castings?

curvy77 (author)robrt maccian2012-09-28

......dont understand much of what u said, but i beleive ur asking if it can melt
aluminum t-6 alloys? for some rifle castings? it depends on what was used to
generate this alloy. Hmmmm, this particular one is just aluminum that has

been heat treated and artificialy aged sooooooo, it shouldent be much of a
problem. however depending on size and quantity of what u want to cast u

may need a bigger forge fire. i myself use a fire pit with a metal bottom, started
with wood with coals later added and with a constant current of air generated

by a (small) carpenters blower. the carpenters blower has about 3-5 times
mor force than a hair drier and a wider front. this means more air and more heat.

AustinMiniMan (author)2012-03-10

Hi, Was wondering...what silver were you melting? I was hoping to use coin silver, which is 90% Silver, 10% copper. Would you be able to melt that in this forge? Also, if you could melt it, why wouldn't the crucible, being copper, melt?

curvy77 (author)AustinMiniMan2012-09-28

melting point for silver is about 1790. which is plenty lower than 2000. so you should have no problem melting the silver part. however i recomend that u put this coin silver in an iron or steel caseing (held by pliers) with holes in it to drip into a crucible. this way u can get pure silver and be rid of the copper. (copper melting point is 1971 F)

curvy77 (author)2011-12-20

can soft clay be substituded for plaster or does it have to be baked clay?

0087adam (author)2011-08-24

Hmm i have some modifications to the original design that i will implement in my furnace. Isn't the lime in the concrete explosive at certain high temperatures? I'm also wondering what kind of metal your melting down and if this will go hot enough to melt steel or iron.

Avasar10000 (author)2011-02-21

Is this method sufficient for casting silver?
Would the crucible need to be a different material?

spylock (author)Avasar100002011-07-03

Melting pt. of silver is about 2000 F.if he were to use map gas which will hook to the tourch he has he may be able to melt it,I do know map gas gets a couple of hundred + degrees more than propane.Mapp gas comes in a yellow disposible tank and is available at any home

spylock (author)spylock2011-07-03

M.P. for silver is 1760 F and using map gas in his setup he shouldnt have any problem melting it.Using a Turbo tourch head will give him an even higher temp though they cost about 3 times as much as the generic tourch head.

bono80kuriks (author)2010-06-05

so just to get this correct....... the wire that you taped to your desk in the 5th picture is touching the wax carving so that when the plaster dries there will be a hole that the wax can drain out of. right?

Toastytoes (author)bono80kuriks2011-01-04

And that you can pour metal into.

annaliesa! (author)2010-11-26

THe paint can /quickcrete furnace idea is pretty cool in theory- I'm concerned about the chemicals in the quickcrete- I checked out their msds - lots of hazards which could be exacerbated by heating the concrete up to metal melting temperatures. Furnaces are never made with commercial concrete, they are made with special bricks that are designed for high temperatures. The only reason I am concerned is that I've thought about making my own furnace but decided not to because of the hazards. Otherwise a great idea! I LOVE your mold/casting demo!

solarmew (author)2010-11-03

i just looked at the Quikrete website and there's like a million different quikretes X.X ... which one is the best to make furnace with?
In the FAQ it says that to repair a fireplace they have quikrete that can withstand up to 300 F, but isn't that kinda low for a furnace?

Don,t try this at home (author)2010-07-23

how would i make a 2 part mold like if i wanted to use my grenade and make a mold of it and fill it with aluminum how would i put those 2 molds together

This is just a basic brief on how to do it 1) get some playdough/ poly clay/ mouldable clay 2) mould clay onto one half of item and let dry/set 3) mould clay onto other half (making sure both sides don't join (talc powder works well) 4) when both sides are dry, remove item 5) hold together and make a hole to pour in liquid wax (hole can be made on previous steps 6) pour in wax 7) remove wax blank and tidy join 8) Add a wax sprue 9) suspend in plaster with sprue poking out of top 10) when plaster is set, put upside down in an oven so wax melts out 11) while mould is still hot, pour in metal

avatardub (author)2010-05-23

hey can i make ceramics instead of concrete part ? thanks !

EMC45 (author)2010-03-19

Have to agree with robotmastern. The buffing compound is probably a bit course for the jewelry. Red jeweler's rouge is where it's at. Than hit it with some white rouge and you're in business. AWESOME instructible all the same. I have had in interest in lost wax since the early 90s in high school. You have revitalized it!

robotmastern (author)2010-03-04

 you could find a jewelers polish at your local hardware store and get the metal to be a nice mirror finish, don't use it on stones though it doesn't come off and just gets trapped in any grooves.

seabeepirate (author)2009-06-07

I think I'll be building one of these this weekend. The first practical item I wanted to make is an adapter from my CO2 tank to my welder. Without the centrifuge could I cast, say aluminum, and get the detail of the threads on the tank or will I have to make the hole smaller and thread it after casting? I'm trying to avoid spending $100 on the adapter if I can.

Thoth (author)seabeepirate2010-02-18

Better off casting slightly larger and then using a tap and die set (if you don't own one rent or borrow or just buy one) to cut the the threads.

swighton (author)seabeepirate2009-07-25

I think it is unlikely that you would be able to attain the detail of the threads without a centrifuge. If it was an extremely coarse thread you might possibly (I repeat POSSIBLY) be able to cast it with the "thread" part of the thread slightly wider than it needs to be, then file it to shape. The other worrisome thing would be surface finish of the seals. It might require a bit of finish machining on the o-ring seats to attain a good seal.

Asbestos (author)2010-02-08

Another question: (thanks for your previous answer!)

In your materials you list a 1"x7" pipe. I assume that this is the pipe that goes inside the quart can to make it hollow.

But my quart cans are only 5" deep. Are you using can with another dimension?

And a 1" diameter hole seems way too small. From your last picture on Step 2, if that small copper cap is 3/4" in diameter, I'd estimate that your inner hollow is at least 2" in diameter. Would you say that sounds right?


(I'm setting this all up in my workshop right now, and keep getting confused by the various dimensions listed)

Asbestos (author)2010-01-28

Question: Is curing the concrete in this way (drying for 2 hours, then the oven, then the blowtorch) better than 24-48 hours drying on its own? Is it just a matter of doing it faster, or is it actually better?

Also, I'm a little confused by the direction the bottom pipe is supposed to go in. In your pictures on step two, it looks like the pipe (and the blowtorch's flame) go straight towards the center of the furnace.

swighton (author)Asbestos2010-02-02

I don't know if allowing it to cure for 24-48 hours on its own gives better results. I would image it reduces your chances of the concrete cracking because of internal stresses from uneven cooling. If i was doing it again I would probably let it cure for two days. In this instance I was in a hurry.

The pipe is supposed to be approximately tangent to the wall of the inner part of the furnace. The idea is to cause the heat to convect around the crucible rather than heat up a spot on the side of the crucible thats touching the blowtorch. My implementation of it sort of failed (e.g. I didn't get the pipe orented properly) and as a result I burned a hole through several crucibles because of the intense heating in one spot. Basically follow what I wrote and tried to explain, not what my picture showed ;)

heavyhadron (author)2010-01-13

There are other alternatives to purchasing or making a centrifuge that I have used with varying success to get fairly fine detail in my castings.  The usual disclaimer applies here - there are many ways to hurt yourself doing this.  Use caution, follow shop safety rules, and stay aware of what's going on and you can minimize the dangers present.  I am in no way responsible if you hurt yourself doing this.

     One alternative is to steam cast.  Instead of putting your wax into a foam cup, put it into some sort of metal can (soup can with top and bottom removed works) - this is called the casting flask.  Also, make tubes of wax and weld them onto the back of your wax piece (they are called sprues) at multiple points to allow the metal to flow evenly.  The farther the metal has to go, the less detail you can put into the piece.  Also, at the other end of your sprues, you want to make a small bowl shaped area to hold the metal as it melts (this will act as your crucible now).  But more importantly, this depression (called a "button") holds in extra heat so the metal will stay liquid longer as it flows through the mold.  Pour your plaster around your piece and cure it.  Burn out the wax (heat it in your furnace until about 500 degrees, or until all smoke has stopped coming out.  Place the metal to be cast into the button now and put it back into the furnace.  Let it all get nice and hot, melting the metal in the button, or getting it close.  Then pull the whole thing out and place it on either a firebrick or on some concrete.  Heat the metal up more using a torch - you want it nice and liquid, and you will see patterns swirling around - that means it's hot enough now.
     Now comes the fun part.  Wear some type of gloves while doing this - I use gardening gloves that are soaking wet, stuffed with wet paper towel in the palm - this give me good control and still gives some protection.  While you were waiting for the metal to melt, you have prepared a lid from a pickle jar, or spaghetti sauce jar (metal, threaded lid) by placing a couple of folded paper towels into it and getting it wet.  Take this wet jar lid/paper towel combo and place it on top of your casting flask and melted metal (which is still liquid).  Press down HARD - use your body weight!  You will hear the steam hiss, and hold it down for 30 seconds to 1 minute.  Congrats!  Your piece has now been steam casted!  I like to throw the whole thing into a bucket of water and the plaster just crumbles out, but remove from the plaster and finish as you see fit. 
     A note - it helps to have more metal in your button for steam casting than other methods - the button is a heat battery, basically and the steam will consume part of that.  So to compensate, melt more metal when you cast this way. 

I hope that helps you in you casting fun!  It is certainly the most fun way to cast for me. (author)2009-01-03

i take it you could use plaster of paris instead of faster plaster?

swighton (author)mr.space2010-01-06

Yes - faster plaster is just a microwavable version of plaster of paris, it allows you to cure the molds quickly in the microwave instead of waiting a day

spylock (author)2010-01-06

Lead is deadly,and shouldnt be used for anything,craft or household wise,we dont even use it in plumbing anymore because of the toxic effect and it dosnt take much.

thoraxe (author)2009-06-13

hmmm....this could have been better. what you should have did was carve a "sprue" into your wax model, which is basically a small cone whose point touches the model. then you would make the mold around the entire model, leaving the widest part of the cone uncovered. this forms a nice opening for metal to flow into. basically this allows much more intricate shapes to be made without having to have that open casting.

swighton (author)thoraxe2009-07-25

I agree! Though the only way to attain more detail via a sprue is to use it in conjunction with a centrifuge - I made a centrifuge from a bicycle very checaply, I detailed the process for a ring I made using centrifuge casting on my website. You can check out the link here.

tjk94 (author)thoraxe2009-07-14

Actually if using a clothes hanger to hold the wax well the plaster is drying it wouldn't be that hard to do. Just mold it as usual but completely cover the wax with plaster, melt the wax out then widen the hole from the clothes hanger.

nodrog19 (author)2009-04-16

What did you use for a crucible?

nodrog19 (author)nodrog192009-04-17

BTW, using plaster instead of cement to insulate the furnace does not work.

sosimonita (author)2009-03-22

This post saved me money on classes...thank you

dciocoiu (author)2009-01-09

what is Quart paint and can i find it at home depot?

TheDeviant13 (author)dciocoiu2009-03-20

dciocoiu all it is is an empty paint can that held 1 quart of paint in it

chemisti3 (author)2009-01-19

where did you get the epoxy.. i cannot find specifically the clear drying marine grade epoxy... the marine grade epoxy ive seen are white drying... can you give some specs of the glue you used?

dciocoiu (author)2009-01-09

What is Quart paint and can i faind it at home depot?

ggiihh1 (author)dciocoiu2009-01-18

Quart paint is just an empty quart sized can of paint. The metal kind not the new plastic type.

stephenniall (author)2009-01-02

i did this with silver but instead of earings i bought 1.5m SIlver wire (99.9 % silver) off ebay and cut it into small pieces together then melted it down it turned quite nice (ps wire only cost something like £5 ($10) with postage)

Mig Welder (author)2008-12-20

thanks! very clear, easy to follow, easily obtainable materials :)

lkllb2 (author)2008-11-21

I am in the process of trying this! Great instructable! I'm glad I found this or I would have spent a lot of money on a comercial one lol....

Carlos Marmo (author)2008-10-29

Wonderful Work! Congratulations!

About This Instructable




Bio: I am a mechanical engineering/computer science student. I currently am very interested in engine design and just about anything else. A look at my ... More »
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