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Lost Wax Castings

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I haven't been on the forums for years, but I recently got an idea to lost-wax cast a ring. I have tried searching various sites to find out more on this subject (I have found a good deal at instructables.com), but I have no idea what to use as investment. It doesn't tell you on any of the sites. Can someone help me out? I had thought about using Plaster of Paris, but I have no idea if it can withstand the heat (I'm going to be casting copper) I also decided to take a page out of the ancient's book, and use clay. No go. I am somewhat impatient, so I did not wait long enough for it to dry. So exploding mold. Funny, but unpleasant.

So, to recap, what is the investment used to lost-wax cast copper? Can I use Plaster of Paris?

Also, I'm not sure if this is where I should be posting, but it seemed to be the best fit.

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Talk to a jeweler, specifically a custom jeweler. Often they do their own work. These are owner/operators not chains.

Another thought is to use a high zircon ceramic coating, but you will need to fire the coating...which is fine really. This is a kaolin slip with zircon gorg (zircopax) then a "dip" (more like sifted over) in dry kaolin and zircon, then wet etc until a structural coating is achieved. Then the mold on the wax dries for several days, then the mold gets heated to recover wax, then fired to remove residue and vitrify the kaolin. The hot mold is then filled with molten metal.

I know a process of this nature can be used to cast steels, but have no (real) clue of the coating thickness (guessing 1/2 inch or more based on seeing it done once) or the exact mixture. The mixture was applied using robots as the wet coatings needed to dry several seconds before going into dry. Build up would be done all at once.

Hope this helps

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Plaster of paris will work and it will take the heat just fine but craft-plaster (the kind you find in the craft section of a variety store) may not give you the retention of detail you're looking for. Make sure to melt the wax out completely at around 400 degrees then slowly bring it up to about 1000 - 1100 to completely bake the mold.

I do larger castings and use pottery plaster and get good results for my intended purposes but it's been a long time since I've done tiny castings that need a high level of detail and am not up on what the current best product for jewelry is - there's a few folk on this site who may chime in with an exact product to use.

Do a Google search on jewelry casting suppliers - you'll probably find something that will suit your needs and can be purchased in small amounts.

Copper can be fussy to cast - If you're using scrap of unknown type it can pour with very inconsistent results - especially if you're just gravity casting instead of centrifical or vacuum casting.

Good luck - post some pics of the results when you get done!

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Thanks for the fast reply! I just ran into a post on instrutables saying that one should mix the Paster of Paris with pure fine-grained sand, so I might have to try this. I've gotten pretty good at carving wax models by now, so I think that I can afford to experiment a little with methods of casting.

I am interested in why you mean that copper can be fussy to cast, though. I am using scrap electrical wire and a small piece of copper pipe, and you might be able to tell that I am more or less jury-rigging this, so it will be a gravity cast.

Another question just occurred to me. Do I need to flux the metal? If so, can I use 20 mule team borax?

Also, I will be sure to post pictures of the results. And, as I am doing this for a woman that I am trying to steal from her current boyfriend (and have almost succeeded in), so I might post pics of that too. She is still wearing the ring he gave her to show that she is taken, so I hope that she might get rid of that ring (it is cheap, anyways), and wear mine instead.

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When I worked at a foundry we used various grades of silica to build up a mold on the wax trees. Kind of a long process. For small tests we used dental casting equipment. Talk with your dentist/dental lab about doing the casting in their centrifugal caster. Their molds take very little time to make, and they have the vacuum chamber to keep the mold bubble free.

Copper can get oxygen/gases in it that will make a very porous casting. It takes care to make it come out right. Scrap wire, etc is not reccomended in the book I have due to the surface area exposed to the atmosphere. If that is all you have, they say to compress it into as tight of a cube as you can before melting. It isn't as easy as melt, and pour. If I remember right, Lithium is used as a degassing agent.

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It is easier and a better finish to cast bronze (brass) than copper, some additives may help in the pouring if using copper (zinc and its implications)

Good luck and Take care (wear suitable PPE), and lets see some pictures on how you get on and the steps you took to get there.

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Join and ask these folks, they'll tell you more than you ever wanted to know about casting, and other FINE metal working. http://www.ganoksin.com/orchid/orchid.htm

In general plaster will work with acceptible loss risks for relatively low melt metals, copper or bronze being at it's high range. aluminum or silver being low and mid range.

Kaolin clay is proof for casting virtually ANY metal it's likely anyone will cast in a home shop. You can get astounding detail retention with kaolin slip as in a fingerprint on an iron casting detail. Mix the slip to a thin milk shake consistency, dip your wax and let it drain, dip again and while it's draining dust with silica sand. Dip and dust till you have a good chell thickness which is largely dependent on the weight of the casting you're making. A finger ring will not need the shell strength/thickness a transmission casing will. To use an exagerated example for illustration.

The sand is reinforcement, proof against shrink checking and enhances drying time so the shell will dry in a day or two where it might take a week for plain kaolin. Once it's dry, use a little air circulation and a light bulb to speed the process without destroying the shell. Once it's dry place the shell in the burn out kiln sprue and risers DOWN so the wax will flow out into the pan you've placed out of the kiln's full heat or you're going to get a little wax fire. Oh, did I say LITTLE? Maybe for a ring ot two it'll be little but . . .

Here's a trick Bruce Fink swears by and Bruce is a couple steps above a master at casting. Introduce steam in the early dewaxing step, it'll melt the wax a few times faster than dry heat of much higher temp. I think Bruce literally dips his shells in water just before putting them in the kiln but that's from memory and I may, am probably wrong so just put a pan of water in the hot part of the kiln or spritz a bit of mist in the bottom to steam out the wax.

Don't remove the shells after the wax is cleared out, just turn up the temp and fire it where it sits. Once fired and still HOT the shells are ready to accept molten metal.

That's about it but for the hand's on guys opinion check out Orchid on Ganoskin. They KNOW what they're talking about.

Frosty the Lucky.

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Frosty hit on some really good points - the steaming process he mentioned is what I was referring to when I said bring it up slowly to about 400 and let the wax melt out. You don't need to dip the mold in water - pouring a small amount on the top of a dry mold and letting it soak in will accomplish the same thing. You can avoid the wax fire at the higher temps by removing the wax tray before ramping up the temp or if your kiln can accommodate it, a small hole in the bottom will allow the wax to run out of the kiln into a catch tray placed below the kiln (this works with larger wax's but may not work with small pieces due to the tiny wax volume). As I said before, I do larger castings (200 - 400 lb pours) so some of the techniques I use don't translate down in a "1 to 1" fashion.

Be careful if you pour into a hot mold if you're using just plaster without any kind of binder - while you'll get better metal flow, the mold is much more fragile at heat and at high risk of damage if you are using tongs to manipulate it. I'd use a piece of iron pipe as a mold-form - that will give you a much more robust mold to handle.

BigGunDoctor's comments about copper being fussy are what I was referring to but I hadn't heard of the surface area concerns with wire before - it makes sense and I'd follow his advice regarding reducing it.

All of the suggestions you've received are good but predicated on the idea that you have some experience in casting molten metal - study up and because it's an inherently dangerous activity, solid safety practices are essential - it's a trial and error process for a beginner so if you're successful the first time out, count yourself lucky - it may take a number of attempts before you get your equipment and techniques tuned up to where you get good repeatable results.

Looking forward to seeing the results!

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When I was doing jewelry with silver, I used 20 Mule team. I have used it with Brass also. I would expect it to be fine with copper. I used iron muffler pipe for the pattern flask. I never tried straight plaster of paris for the investment. I did steam casting for the silver work I did. Good luck with your project.

Brian Pierson

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  • 10 years later...

i did my first lost wax burnout and pour,... first in 18 years.i was so excited and thought i had done my research well enough. turns out i was very very wrong. i had three flasks 4x6 and one 3x4 flask.  1400 slow ramp burn walked up to 1300F and crashed to 900F before pour. long story short... all of my plaster shrank a lot in the flask and my plaster cracked to pieces ruining my molds and my afternoon. it anybody would like to guess at what i did wrong and make some suggestions i would be glad to take advice or listen to explanationsof what all i might have done wrong. side note i was using green wax sprues and castable resin molds.  plaster used was ultracal 30.. when i examined the broken pieces all of the detail looked amazing and seemed to be a clean burnout with no residueleft over. i assume that the work would have come out nicely if i had the heating program dialed in but the shrinkage was quite excessive. any thoughts or advice would be greatly appreciated

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I was pouring sterling, some earrings, rings,and pendants.  The plaster folks recommendedat least 24 hrs to set and cure out the water content I gave it 72 hrs and they were the light grey specified pre burn.  The castable resin people recommended the 13 hr staged burnout.  A very gradual heat and also cool down.  I was so sure I followed the procedures to the letter.  I checked the kiln and temp control appears To be accurate. 


Now a wax burnout is a lower temp and shorter duration that required for the resin casts to burn out.  I suspect that things would have gone better if I was not using the resin but really dont know.  I'm looking for plasters that are specifically designed for the long hot burnout.  I guess I was looking for someone who might have some experience With these types of issues and could recommend anything that would get me better results.  Was a lot of work to end up in disaster on the last step...


Gonna try again this weekend probably with a less aggressive heat cycle, not confident I'm not wasting more time and materials but to hard headed to quit

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