Bronze Making/Melting Furnaces

[DanM]

I might try to reconstruct a classical age Greek bronze foundry. What did the greeks use for casting sand, crucibles, fuel, refractory, and tongs? Thanks, Dan.

[DanM]

So far, my only references include the gymnasium foundry, and the berlin foundry cup.

[DanM]

Now It's making some sence. For casting sand, can I mix fine sand with olive or vegetable oil, and would a clay crucible be accurate? For fuel, instead of BBQ charcoal, I will make my own, all I need is a steel bucket with a lid. WOuld modern refractory work, and instead of tongs, I could have an iron stick, with 2 people pouring the cast, but I still don't know exactly what the furnace looked like. Also, instead of refractory, is this when the crucible is surrounded by fuel, or the fuel is underneath. If I'm making no sence, got to [url:v2x68z1m]http://www.backyardmetalcasting.com/index.html[/url]

[M. Demetrius]

You can probably buy already made hardwood charcoal (lump charcoal) at regular stores. At least you can in Texas. Making charcoal is not as easy as one might think.

Whatever you use for holding the crucible filled with molten metal had better be a secure grip, or there can be horrendous results. Serious injury or death can result, not to mention burning down the whole house.

[DanM]

I think I saw hardwood charcoal at the grocery store. As for a secure grip, I've been using fireplace tongs, but I may need to change that. My dad does casting for me, because he thinks its too unsafe for me to do. I've already been casting aluminium, but I'm moving up to bronze, in a steel bucket that I stole from a dumpster. But should I use a graphite or clay crucible?

[hoplite14gr]

I will show you some drawings of furnaces coming from Neolithic age if you have patience to wait a week.

Kind regards

[brennivs - tony drake]

I dont think a bucket with a lid on will be any good you are talking about some serious heat needed here, so fire bricks will be a better option to contain the heat, also you could dig a hole in the ground and line it with clay wink: So stay safe I will see if I can dig out info on the subject
Regards Brennivs

[Endre Fodstad]

The melting point of bronze varies with the alloy (look it up) but to properly melt it, you need a furnace that reaches temperatures around the crucible at upward toward 1200 degrees or so, or it is going to take forever and the metal won't flow properly. It is very different from casting aluminium - aluminium, like tin and lead, is forgiving to cast. Bronze is not - bronze is a temperamental metal that needs just the right temperature and steady pouring to succeed.

I do not think sand casting has been confirmed as used in greek antiquity (the first reference I know of for it comes from al-Jazari's "book of ingenious mechanical devices" treatice in the 12th century - of course, sand casting leaves almost no tracks for archeologists to discover, so it is difficult to say exactly when it appeared) and I strongly recommend using commercial casting sand (with oil) instead of making the sand yourself..just in case.

On the other hand, sand casting is less time-consuming than lost wax and easier to start up (and far more adaptable) than soapstone casting (both of which have been in use since the bronze age).

I recommend starting with modern tools to begin with before you start reconstructing historical furnaces and equipment. I still use graphite crucibles when demo'ing as it saves time and saves me worrying about the crucibles breaking on repeated use. The furnace is going to be HOT - the furnaces you see in the last two pictures are made from baked clay/horseshit/sand - the same material we make our lost wax molds out of. It has to be rather thick-walled to resist the heat. For my home castings I use a Molochite furnace and heat the crucibles with gas.

I have to admit not being an expert on greek bronze age casting - my focus lie between the 9th and 14th centuries, as in many other things.

Be careful. Preferably, get some hands-on instruction from a pro.

Here is a link to a picture (damn silly 800x800pic size limit) of Ralph Napolitano (Iowa University's) theorethical reconstruction of a neolithic/early bronze age two-way draft furnace based on furnace ground remnants from a set of excavations in Israel. The draft has to be delivered by two "sack bellows" blowing simultaneously. It takes forever, since the draft isn't constant, even with the small self-draft from the chimneyesque furnace.

http://i206.photobucket.com/albums/bb10 ... tping4.jpg
http://i206.photobucket.com/albums/bb10 ... onique.jpg

Yours truly (right, in the lightly colored apron) casting in a ground-level viking/medieval bellows-driven oven with awlstone (so you don't need that pesky two-way draft and can get a constant stream of air).



From this gallery: http://www.kongshirden1308.no/galleri/2 ... thumbs.htm

And finally friends of y.t. (and y.t, check the gallery) casting bronze cauldrons in a self-draft 12th century furnace as described by Theophilus Presbyter:

and associated gallery: http://www.kongshirden1308.no/galleri/2 ... thumbs.htm [/img]

[brennivs - tony drake]

Endre this is great stuff brillant pics ( cry: So could only correct them on the fuel they used to smelt with. Again great advice
Regards Brennivs

[DanM]

I read the temperature on melting bronze is 1750 F, which I believe corrseponds w/ your temps. But I need to get it to about 2000 F, about 1100 C. My modern furnace, I can roughly base designs off of it. It will use a steel crucible, a steel bucket to contain the fuel ( lined with refractory ) , a bathroom fan for the blower , and an expendable carboard tube to connect the blower to the furnace. I could use my foundry buddy to portray the slave, and we could switch. But did the greeks use billows, because I read that they just used the wind by putting foundries on hills.

[Endre Fodstad]

The Berlin Foundry Cup shows a greek 5th century furnace:
http://www.perseus.tufts.edu/cgi-bin/im ... 86&image=1

Mattusch examined this in a 1980 article: "The Berlin Foundry Cup: The Casting of Greek Bronze Statuary in the Early Fifth Century B. C" (American Journal of Archaeology, Vol. 84, No. 4.). He follows traditional assumptions and makes the guy behind the furance out to be operating the bellows.

Hoffman and Konstam wrote an article in 2002 "Casting the Riace Bronzes: Modern Assumptions and Ancient Facts" (Oxford Journal of Archaeology 2002, vol 21 issue 2) that assumes that the greeks must have used natural draft ovens for their larger pieces, because it would have been impossible to melt such large pieces as the torso with tall bellow-ovens. They call for further study to find these furnaces and casting pits (who must have left easily discernible tracks - archeology has uncovered hundreds, possibly thousands, of such casting pits from medieval times, primarily for church bells) but so far, no cigar, and they don't refer to any actual attempts to produce statuary torsos with bellows so the burden of evidence doesn't favor them. It wouldn't be the first time modern craftsmen or practical archaeologists declared a historical method "undoable" only to have it stuffed back in their faces by experimentation later on

That being said, a combination of natural draft and bellows is also quite possible - when our field-built furnaces don't produce the requires heat we often help at bit at the end with bellows. Of course we rarely go above 20 kilos for field castings.

But anyways, yes, the greeks used bellows for casting smaller pieces, at least. Go to town.

[brennivs - tony drake]

I once saw a program Man on the Rim, the program was in china and showed a Iron furnace with a bloom in side as the furnace had failed they left it and it was excavated nearly 2000 years later and it weighed in at if I rememmber right, 38 ton it also had a casting floor. So if you were to cast in bronze in any great size then I can not see any problem. On draft shaft furnaces some are knowen in Britain one was even on Time Team that had a tavern built over it. and it would still need bellows to drive it as you cannot always gaurantee the wind will be there. Even the smelter we built has left very little evidence of what was on the site not even a heat stain on the ground.
Regards Brennivs

[Matthew Amt]

Ave, Dan!

Been to the Bronze Age Center, I presume?

http://s8.invisionfree.com/Bronze_Age_Center/index.php ?

Browse through the threads to find all kinds of great information, particularly the Reconstruction FAQs, and Palace Discussions. Also Jeroen Zuiderwijk's excellent site,

http://1501bc.com/index_en.html

http://1501bc.com/nf_casting_eng.html

Good luck and BE CAREFUL!!

Matthew

[DanM]

Endre, what is the crucible made out of?

[Endre Fodstad]

Endre, what is the crucible made out of?

Graphite (as stated earlier) because it is easier. The originals were clay, of course.