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enitharmon 08-12-2007 01:25 PM

Re: Bronze Clay?
Jonn the activated charcoal sounds good [for small pieces?]. How large was the container you put it into...and how long did you fire?..good to hear of your success too.
Daniel, I mentioned on a previous post the patent for freezing and pressure, it also had analine???in the mix. Don't know why though.

jphariot 08-13-2007 12:35 AM

Re: Bronze Clay?
Daniel and Enitharmon,
It doesnt smell, it is not dirty, its great. It looks like coffee grinds. And it seems to last. I understand it just burns away and leaves little ash.
I like the consistency better than my tests with gas. And i already filled the bottle 2x. This seems way cheaper.
As far as large pieces??? Well yes, I am doing small jewelry sizes. But I dont see why I couldnt do cabinet pulls, or even bigger. Just need more charcoal.
Right now, I am using that. I want to work with stainless steel. I have some sample powder coming next week. I dont know if this will work. One source told me that stainless needs nitrogen-hydrogen or vacuum. I would opt for vacuum at that point, but I am going to try the charcoal first.
I am also ordering some Wax powder tomorrow. What about a small amount like 5% of wax powder and metal mix. Then bake in oven to sinter the wax.
Then demold and sinter in kiln. I know that I will produce propane, but it will be small amounts. Not like the other method though. So then what about another thermomelt natural binder?? Can you guys think of anything?
I will send more pictures soon. Next time larger. Those were hard to see.
Thank again,
John H.

ara 08-15-2007 02:02 PM

Re: Bronze Clay?
hi all, been trying to post on this thread for a while but not being allowed in for some reason.

anyhoo, very very interesting everything you have said and some great pics..

my thoughts: doesnt oxidised bronze just have a thin layer of darker 'stuff' (sorry dont know the techincal term) on the surface which can be removed easily with a piece of wire wool thereby meaning that it is not a huge problem if the bronze is already oxidised to a certain extent? plus couldnt u cover it with any patina you wanted (including natural bronze colours) ?

same goes for aluminium as far as i know..

what is the jacket for the moulds made of? its silicon rubber for the inside but that has to be supported by something? as this (in the case of the clay..i think) doesnt go in the kiln, then it could be fibreglass or plaster right?

when it does go in the kiln (i.e bronze wax method) what can it safely be made of?

i have little to no experience with ceramic firing but i have been told NEVER to combine plaster and clay in a kiln or things go boom...?

so if your plaster jackets were in the kiln with the clay, would that not then explode? ..burkhardt what have you been using?

has anyone had success with the direct modelling method as yet?

how do you create a vacuum kiln? or is it easier to just buy one?

can you use a hoover in some way ( ive heard whispers of this but nothing concrete)

i am interested in ressurecting this method, i cant offer much in the way of technical expertise (i have been casting bronze and iron in traditional furnaces for just a short time) but can be an extra hand for collecting supplies or something.. im sorry ive lost the name of the person who originally wrote the 'ressurection' post, were you in england? im london based so i hope so!

i am due back at my college in september and will try and get the tutors excited about these processes, perhaps we can come up with something which will help.. at present i have next to no facilities to try anything out.

can someone please explain what would be the result if you fired the bronze clay with bentonite in an air kiln? would you get a pile of dust?

cheers for the help


DanielUCM 08-15-2007 02:18 PM

Re: Bronze Clay?

Originally Posted by ara
my thoughts: doesnt oxidised bronze just have a thin layer of darker 'stuff' (sorry dont know the techincal term) on the surface which can be removed easily with a piece of wire wool thereby meaning that it is not a huge problem if the bronze is already oxidised to a certain extent? plus couldnt u cover it with any patina you wanted (including natural bronze colours) ?

Hi Ara!

Normal cast bronze would have just a thin layer but the problem when dealing with metal in powder form is that every particle would be oxidised when heated in an atmosphere that contains oxygen. And basically they can't stick to eachother (sinter) if they are oxidised. Therefore the need to create an atmosphere free of oxygen using gasses such as nitrogen or co2, or the latest thing we have discussed, activated charcoal.

No mould is put in the kiln. The idea is to either use a binder that binds the metal particles until they are sintered (as John is experimenting with and which is how its often done industrially). Or to bind the particles during the time when the sculpture is demoulded. When it is demoulded it is in that case placed in a powder which makes it keep its form when the binder is removed or weakened. Different binders are removed at different temperatures. My method of using bronze ice means that it only need to reach room temperature for the water to be wicked from the bronze powder and then higher temps for it to turn into steam. The bronze wax method means that another temperature must be reached for the wax to melt and than turn into a gas that can be extracted from the kiln. With the bronze clay method the water that has not already dried leaves the sculpture.

By the way, I'm right now making a test run of product samples of bronze powder I have gotten - soon I'll have a batch here so I can go at this seriously!

/Daniel S.

ara 08-15-2007 05:49 PM

Re: Bronze Clay?

Originally Posted by jphariot

I did my first test last night. Into the plaster molds. Failure. Got a black piece of charcoal. Oxidized to hell. Not sure why. I will try again this week sometime.
Thanks all,
Johnn Hariot

how about if you dry out the plaster mould thoroughly in the kiln first so there is less/no oxygen in it?

would that work?



ara 08-15-2007 07:08 PM

Re: Bronze Clay?
does anyone have the name/isbn of the book Rand German wrote?

i tried googling it but didnt come up with much..

i think that would be well worth a read

Harryman 08-16-2007 09:39 AM

Re: Bronze Clay?

how about if you dry out the plaster mould thoroughly in the kiln first so there is less/no oxygen in it?

Unfortunately for our purposes, oxygen is everywhere, even inside of plaster which is porus. So to have a shot at successfully sintering bronze, that oxygen has to either be sucked out with a vacuum pump, absorbed by another substance (charcoal) or driven away by flooding the interior of the chamber with another gas.

enitharmon 08-16-2007 11:24 AM

Re: Bronze Clay?
Ara, Professor German has written 17 books has 22 patents and some 230 published articles also the books are quite expensive 200+ so if you are at college/uni you might get access through the material sciences faculty.

Daniel, good luck with the powder, was it spherical or irregular and what mesh or micron size did you opt for. I've just got some powder too, so will see how it binds when I get all the hardware 'in situ'.

DanielUCM 08-16-2007 06:11 PM

Re: Bronze Clay?
Enitharmon - Good to hear you've getting it all together! The samples with finer grain size was <60 micron, if I remember correctly. One of the samples was spherical (the one that contained some P). The one without P I believe was more irregular but I will check back with the supplier when I order so I have all the info. Anyway the powder without P, which is very similar to the one I have used earlier, worked out better than the one with P. I was surprised since the one with P mixed really well with the water-mix and I thought the phosfor would aid with the sintering. But I will order some of that anyway and do some more tests with it.

I used more gas this time so I got better results than previously, its beginning to look better! Tomorrow or the day after I will run a crude test using activated charcoal. I've only gotten ahold of pellets rather than powder but I'll see what happens.

Unfortunately I haven't done any more tests using steel powder with a proper atmosphere yet since I have to fix some better container and tube for the higher temperature before I can do that. I have at least three kilos of various sorts just waiting to be sintered. We'll see who makes it first!

Best wishes
Daniel S.

ara 08-17-2007 05:35 PM

Re: Bronze Clay?
ok, will try a more thorough search for one of the 17 (!) books later

yep oxygens a pain in the butt, i guess vacuum is the way to go then..more reasearch to do!

daniel have u got a pic of the latest one?



DanielUCM 08-21-2007 05:51 AM

Re: Bronze Clay?
Hi - A few days ago I made an attempt using activated charcoal. I bought at the nearest aquarium store and they only had granules (pellets), about 250 gram. I put some in the bottom of a can and then put some of the aluminium oxide as a base for the bronze. Put more powder on top of the bronze and then covered it with the rest of the activated charcoal. Put a lid on top of it. Sintered as usual.

The result was an absolute failure! Both pieces were really soft and spungy - really strange! Ok I haven't done my homework on this particular method so its no surprise it didn't work. Maybe it was too much oxygen in the can? The coal only filled like a sixth of the can. Maybe the aluminum oxide powder ruined the effect of the charcoal by intriducing more oxygen? I don't know. I'll probably do another better organised test in the future.

Anyway, right now I'm glad that the bronze ice co2 method is working out better and better. I have no picures since I have only had so little powder that I have just made small test pieces. My supplier is just waiting for a shipment to arrive before I get 25 kilo of bronze powder! Maybe I'll have to get some nitrogen before making the first tests of steel in an oxygen free environment?

Daniel S.

jphariot 08-22-2007 02:58 PM

Re: Bronze Clay?
Just a small stainless container with lid. Wasnt too much bigger than the part.
Maybe that is the trick. Whats difficult is you may do something once or twice and it works. There are parameters and I am not sure what they are. I just have to keep trying it different ways. But the couple I did seemed to work.
The last few had huge cracks and blisters Drying too quick I bet.
I was talking to a supplier that said vacuum is the best. It shouldnt be hard to do. Just place an electric kiln inside of a steel drum with a lid and seal essentially.
Glad your Ice is getting better. As soon as I solve my cracking problem, IE proper drying. I will post more photos. I am going to be joining you at some point with more ice tests. I also have another thermo binder idea which I will be trying soon. I will fill you in on what happens.
Back to work for me!!!!

Pzak 11-06-2007 12:04 PM

Re: Bronze Clay?
Does anyone have a good/cheap solution to sealing the Stainless Steel pot inside the kiln so the "natural gasslike" gasses don't leak? If I recall, someone tried putting plaster around the lip, but it cracked.

Burkhard 11-12-2007 10:23 PM

Re: Bronze Clay?
Mmmh, this thread seems to have died out in the last couple of months. No interest, too difficult or were the results not up to scratch????

Did anything ever work well enough with the freeze casting of bronze powder?
Any further news on using charcoal instead of inert gas atmosphere?
Did Rio Grande ever put out the bronze clay kit?

Pzak - I tried sealing the lid with plaster of paris, and later on I tried using a "bat wash". Both cracked on drying and then firing to 900C. Neither sealed the pot properly. I guess, ideally you want a properly machine lid with a number of nuts/bolts to seal the lid onto the base. Last few times I just used three steel weights (about 2 kg each), placed on top of the lid, to get a reasonable seal around the lid of the pot.

This works well enough to maintain an inert atmosphere, but still leaks a little. This is not a problem if using the bronze clay or frozen bronze/water mixes, but is a potential problem if doing the bronze wax method - main worry is generation of carbon monoxide, which could leak out of the kiln rather than being burned up in the outlet exhaust. Someone earlier on in this thread suggested getting a carbon monoxide sensor or alarm - a very good idea. Let us know how you get on.


DanielUCM 11-28-2007 07:37 AM

Re: Bronze Clay?

Burkhard - The methods are surely not dead for me! My 'problem' is that I have started ph.d training while at the same time being stuck in work from before becoming ph.d. candidate (Just returned to Sweden today after a trip to the UN in relation to a report that I co-authored earlier - have to write a five page memo for a methods course now until tomorrow.. while suffering from jet-lag..). So I have had very little time to experiment lately.

As far as pieces that are more solid the bronze ice method works really well so far! I just have to get a new tube right now that fits the container better, just always forget about it.. Eventually need a bigger container too. I have gotten some 25 kilo of bronze powder a couple of months ago so me and my brother can actually start to make stuff beyond experiments now.

My last cutting edge :) experiment involved making a piece with very thin walls, it was however a failure. There are a number of reasons why, amongst others the fact that my freezing capabilities were not really up to the slightly bigger job, compared to my earlier tests. Now, however its -8 degrees C outside so I can use natures own freezer so hopefully I will be able to replicate my latest experiment soon! I just wanted a succes before telling you guys about it!! At the latest I will have a few vacation days around Christmas and get back to you after that.

So let's here how you other guys are doing! How is it going for you Burkhard?


Daniel S.

sebastinbailard 12-16-2007 07:13 AM

Re: Bronze Clay?
This is a fascinating thread; I'd stumbled across it earlier this year when it was only speculation. I'm sincerely impressed with what you guys have gotten up to.

A few thoughts:
jphariot mentioned using powdered polyvinyl acetate (wood glue); for that I'd call one or two local industrial adhesive suppliers.

Sealing the lid: if you are desperate, you could try sodium silicate and powdered vermiculite. This would form a refractory cement, which might be too effective.
I'd try a generic low temp earthenware glaze or investment, although that's guesswork, I've never operated a kiln/furnace myself. (yet)

Using plaster in a furnace: At 150C, plaster turns back to gypsum (and turns to powder, I think). It might be better to use investement, which can handle molten metal.

As a vacuum chamber to go in a furnace, you may want to try using an old pressurized paint pot. These stand up to vacuum pretty well, and are often used for debubbilizing casting / molding compounds.

It may be useful to debubble the bronze/binder mixture before pouring it / working it. This would reduce the incidence of bubbles on the final object if this is a problem.

By the way, you guys tend to occasionally forget to mention somewhat useful things like firing temperatures, firing times, what model number/supplier bronze powder you've been using, precisely what type of wax, what particular recipe was successful, and so on. It might be worth jotting this down when in your comments because it will make it much easier for other folk to recreate what you're doing.

Finally, you may want to look at using powdered polycaprolactone rather than powdered wax. For example CAPA 6406, from,00.html
Free sample request page:,00.html
Powder is probably easier to mix than pellets.

Caprolactone, aka 'friendly plastic'
is great stuff; it melts around 60-80C. I like to use the following technique 'pour hot water on pellets of it, fish out a gooey mass with chopsticks, hand work it' technique. Cold, it's about as hard as nylon. It's nontoxic (when not loaded with bronze powder or other contaminants), and is used for splints and sutures. It does tend to stick to tools and pots, but I haven't tried loading it out with large amounts of bulk filler. It may be necessary to use a mold release agent.

My group is actually using it to make constituent working parts of 3D printers / and as 3D printer feedstock, and I'm interested in printing objects out of bronze powder/caprolactone.

Burkhard 12-16-2007 08:30 PM

Re: Bronze Clay?
Daniel - good luck with your PhD! Hope you get some time to try your bronze ice stuff still. I'm hoping to do some (more ambitiuous) bronze wax trials over the christmas break. I won't be playing with the bronze ice stuff though given that I'll be spending Christmas by the swimming pool :). I've finally managed to buy a camera again so will also hopefully get around to taking some pics of my efforts.

Sebastinb - thanks for the input. (BTW - the plaster when fired to high temp still remains very hard, but simply cracks too much to be useful. I'm still playing with this part of the process).

The caprolactone sounds like interesting stuff. Main potential problem that I see with using any polymer is that you have to get rid of the polymer from around the bronze particles as you're firing the bronze powder. In the absence of air the polymer will char and convert to black goo, which will probably coat the bronze particles and prevent sintering. That's where the original bronze wax method is neat - the wax is first removed by flowing into the surrounding aluminium oxide powder where it doesn't matter whether it chars/burns or whatever. The ice method is neat because the the ice/water simply evaporates.

With regared to the details - there's a lot of info in the thread but I totally agree, it's scattered all over the place, some of it's missing and difficult to find. I have vague ambitions to write up the info in this thread at some stage (don't hold your breath though) - does anyone know a place similar to photobucket where one could dump (large) pdf files?

racine 12-17-2007 06:42 AM

Re: Bronze Clay?
i am not against experimentation by far but i do feel that there are some dangers with microwave tech, eg brain tumors, sterilisation etc. dont forget that there is an established electrical method, ie induction, if someone could bring a devise down in cost it would be a genuine innovation.
in 1999 i missed a course by David Reid at the royal academy london but my friend attended. he mentioned microwave but was very wary of passing on info, perhaps we now know why. i suspect that its very good at tiny pieces, lower melting temp/oxiisation, but im not sure, theres always a chance. what about cores? too much to read through all this stuff however interesting.
in short can i suggest the people running this thread make a thread2 with an initial summary
so that others can contribute or ignore or...u never know. perhaps some traditional foundry knowledge could tip the scales

DanielUCM 12-17-2007 07:20 AM

Re: Bronze Clay?
Sebastian - Thanks for those pieces of information. Getting some form of vacuum equipment is one o the next items on my list before being able to get fully satisfying results. Even with the method I have experimented with the most, there will be some bubbles if the mixture isn't debubbled at some stage.

Burkhard - I am also thinking on doing some experiments with the wax method. Like I have thought earlier, it will probably be necessary to use that method for some projects. Looking forward to seeing more pictures!

Agree that this post is getting a bit too cumbersome.. There are a few clarifying posts along the way, though. Look for when Burkhard starts to get in on the thread, he has some good summations of Pilato Bronze Wax procedure, and than some more on the Bronze Clay idea. When I get some more time to experiment and begin establishing some consistency in the results I will write down a summary about the Bronze Ice method. That can take some time before I do though..

RedArt 01-15-2008 11:24 PM

Re: Bronze Clay?
Hello ,
My name is Ron DeRutte and I teach metal fabrication and casting at
Syracuse University in Syracuse ,NY. This is some very interesting work
your involved in and I've been interested in bringing some new methods
of casting to my students. I have a small Duncan ceramic kiln that I will
convert for sintering and have the means to build an airtight stainless
vessel to receive the flask with the wax object. I'm busy building a burnout
kiln for ceramic shell casting right now, but when I get the time I will
get a casting unit built. The bronze ice is extremely interesting as well
and I will be trying to use Aluminum oxide and coilldial silica as a binder
and then freeze. The material should gel and then can be removed from
a rubber mold and placed in an oven at 220 to 230 degrees F. this should
drive off the water and you should have a solid aluminum object. Does this
sound right? Keep up the good work and I will be staying in touch.

Burkhard 01-16-2008 11:24 PM

Re: Bronze Clay?
Ron - welcome to the "club".

I'm not sure I follow what you were suggesting with the alumina and silica.

If you're thinking of mixing the colloidal silica with the bronze powder, allowing it to gel and "set", then that might give a solid object that's firm enough to be cast and demoulded and that might be able to be fired/sintered to give a bronze.

However, if you're wondering whether aluminium oxide + colloidal silica will give an aluminium object after heating, then the answer is no, won't happen. If you heat it high enough you'll get a "ceramic" object.

Last couple of weeks I started playing with this again. Couple of observations on #$%^&* problems I've encountered:

1) sometimes I get blistering/bubbling of the surface - irrespective of whether I use the bronze clay or wax or other stuff. I suspect that this is due to firing the bronze too quickly and the water or wax doesn't have a chance to slowly leak out of the bronze powder into the alumina powder.

2) at one stage, when I was firing samples that did not contain any wax, all I was able to produce was copper oxide powder - no sintering. I looked at my notes (notes - sometimes I pleasantly surprise myself) and with most of my successful previous firings I had always had a piece of the bronze wax in there as well. I added some lumps of wax to the next firing, it worked again. Mmmmh, not sure whether this just means that my lid leaks like a sieve and I need to increase the inert gas flow rate, but I'm starting to wonder whether the decomposition of the wax produces a reducing atmosphere (i.e. carbon monoxide) which will reduce any surface copper oxide to copper during the firing process. Don't know, but I did come across a paper where they used carbon monoxide to reduce copper oxide to copper so the chemistry is possible. I now throw in some wax routinely into the firing pot.

3) Started doing some slightly larger (solid) pieces - carefully drying them,or (in the case of the bronze wax) doing a slow initial heat to 100C to allow all the wax to melt, - didn't get any blistering but I kept getting large cracks developing - very frustrating. I suspect that I'm again firing the kiln too fast (I get to 890C in about 3.5 hours). Also, the 890C is probably too high, resulting in too much shrinkage of the bronze powder. I'll try slower firing to about 860-870C next (the original bronze wax literature suggested only 840C).

Started summarising the thread but haven' gotten very far - too much like real work!

RedArt 01-17-2008 12:10 AM

Re: Bronze Clay?
Thanks for getting back to me Burkhard,
I'm waiting on a technical paper that I have acquired from the SAE
(Society of American Engineers ) on some of the stuff this group is
working on. As soon as I get it and pour over it I will contact the group if
there is anything of merit. I think the biggest problem with bronze powders
is oxidation. That is why I will construct an airtight vessel in stainless
steel. I know there is some cost involved , but if we can get this sintering
business to work consistently, it will be worth it.

DanielUCM 01-26-2008 05:02 AM

Re: Bronze Clay?
Ron - great hearing that you are looking into these methods! I will get back with some more information about the bronze ice method when I have gotten a couple of more trials finished.

Burkhard - I think we have encountered similar problems. I haven't had any real problems when I have made small things, but like I said earlier, when I attempted making a bigger piece (1,5 kilo of bronze powder) it didn't sinter properly. One reason could be that I used ordinary tap water for the ice part, another could be what you are suggesting: That the atmosphere wasn't right. Bigger pieces would perhaps require even more gas than I thought. I have heated my pieces over quite a long time so that shouldn't be a problem. Perhaps I should lower the final heat though. In a couple of weeks I will get my new tubing and then my set up will be a lot more tight, so then I will try to get the time to make a couple of new attempts. I wish I had more time on my hand!!

/Daniel S

mark pilato 02-14-2008 07:43 PM

Re: Bronze Clay?
hi all , you dont have to seal lid, just turn up your gas flow, to about 25, I just placed the lid on the top no gasket no seal, and it worked every time

WillBass 02-26-2008 08:24 PM

Re: Bronze Clay?
Hi all, I'm a new member with no bronze experience, but I signed up specifically to reply to this post, as it is a very interesting topic. Thanks to all who have shared their work, and to Mark for his generosity!

I have a few questions that I'll insert into a brief summings-up of the Process: A mold is created which will be filled with the wax and bronze powder, the powder being the less expensive variety which contains random sizes from fine to a bit less fine. In the process of filling the mold, while the wax/bronze is still a liquid, it is placed in a vacuum chamber and vibrated to remove bubbles.

1. Is this how and why the vacuum chamber and vibratory device are used?

When the wax is hard, it is demolded, and then chased. Then it is inserted into an aluminum oxide powder which is in a small can, and the can is inserted into the stainless steel tank which is sitting in the middle of the kiln, but not too close to the elements, and with refractory bumpers to prevent accidental shorting or electrocution. To avoid oxidation of the bronze powder, a noble gas is piped into the stainless steel tank, using simple tubing methods, at a flow rate of 25. Nitrogen is the gas of choice, as it does not add any oxygen to the mix as CO2 does, thereby preventing oxidation. As long as the pipe in is supplying enough gas, and the pipe out is exposed to flame to burn the gases formed by heating up the wax, the lid can be less than perfectly sealed. Blackening of the sintered bronze results when there is oxygen present, so any blackening should be a sign to increase gas flow or insure a better fit/weight on the lid, without going to the extreme of sealant. The kiln is ramped up slowly, to melt the wax into the aluminum oxide, then a little more to burn the wax, then slowly again to the bronze sintering temp. The temperature is best guaged not by the environment around the tank, but by measuring the temperature in an aluminum oxide powder filled can in the steel tank via a thermocouple exiting the structures and connected to the kiln computer.

2. What prevents the rough texture that has been reported? Mark doesn't comment on it, which suggests that it isn't a problem for him. Those chess pieces look great when completed, and if he's doing it in four days or less, then he's not having to do much finishing work past the expected rubbing/polishing and patina application.
3. Has anyone continued with the activated charcoal powder blanket technique? This would be much better than the tank of gas.

In addition to the bronze techniques, I'm interested in working with copper fused in glass, but the disappointment is that the copper oxidizes when fused. It would be freeing to use carbon as a solution, instead of the gas and tank approach, but one might adapt the gas method to copper glass work and get new results.

4. Has anyone created enough reduction to prevent copper oxidation when fusing glass?

5. Is any of this wrong?

6. Is there something more to know to be able to create sintered bronze in the kiln that has the same look as Mark's chess pieces? Safety/ventilation are to be assumed.

7. Since this wax casting is cold work, and the details are a little troublesome to retain when demolding, would using alginate as a mold material be of advantage? To get a great tooth impression, that's what the dentists use, and it's environmentally friendly.

Thanks again,


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