So it turns out that when refining copper, air gets blown through the molten copper to oxidize iron which is skimmed off, and to get rid of sulphur as a dioxide gas. The next step involves stirring the copper melt with green logs (the person who told me this said he saw "power pole" sized logs used) which give off carbon monoxide, CO2 and methane from the sap which reduces the copper oxides back to copper metal before being cast as blisters. https://en.wikipedia.org/wiki/Poling_(metallurgy)
So it would seem Ammen's talk of charcoal covering of copper/bronze/brass melts has some basis in fact!
I was discussing that topic yesterday (when I heard about poling copper) with someone with foundry experience, he was visiting a foundry where they tossing a black mystery substance on top of the molten bronze that turned out to be granulated coke. He tried it, but had it go with the bronze into the sand mould and cause problems so he used flux prior to pouring instead.
I found this year's ago when I was planning a reverb project. Took me awhile to dig it up. It mentions poling. http://web.archive.org/web/20130801...09/11/smelter-tech-the-reverberatory-furnace/ Pete
According to the description it takes several hours to accomplish in a process that takes 24 hours from start to finish, not to mention being a risky proposition in the first place for the home user.
Indeed, it relates more to your comments in post 1 than it does in your post 3. ie: poles/tons vs cupful/kgs. By the same token the examples of poling we've both mentioned are in the context of refining ore as opposed to melting and pouring an alloy, so utilizing the method might not just be a question of scale (imagine inserting a half-dozen toothpicks in a #6 full of bronze. lol) but also a question of inoculant content and purpose. I know there's a similar conversation currently going on elsewhere. Pete
Needed some good reading with my coffee this morning to get the brain going. I had previously read that when you were discussing your reverb furnace. It's an interesting read, especially since it said when the smelter received the ore it was already 70-90 percent copper. It didn't say whether there was any processing at that point but seemed to suggest it was characteristic of the ore from the lake Superior region.....which would be extraordinary. The read also says poling is the last step in the process before the copper is a pure as it is going to get in the reverb furnace but never says what state of refinement that is, and if I read correctly this was the process being used in 1906. The references in the Wiki blurb seem to suggest it may have still been in use until the 1960s. Is it still practiced anywhere? Seems doubtful because the Wiki article says it's actually the sap in the wood that is the source of the desired Co2 and H2, and although a log might be a practical a practical source in NE USA in the early 1900s, in modern times I wouldn't think so. As an aside, we had a copper mining customer in Chile, and they leached the copper out of the ore in huge open air pits, showered by sulfuric acid, and then collected by gravity, piped away to a near by building where they essentially plated the copper out of the acid solution. I used to have a picture of workers with handkerchiefs around their face walking on planks over the pits as vapor rolled up around them........and this was in the late 1980s. -Not something you would ever see in the US! Things tend to meander a bit in these discussions. That was a discussion of using wood and sawdust to treat melts of several metals where this is discussing the use wood in processing of copper ore.....but there is there is some connection between brass melting with copper smelting. I questioned the efficacy and chemistry cited in using wood to treat a melt of refined metal and particularly whether it was wise or useful for a hobbyist or commercial operation to incorporate such as standard practice of treating a melt. I would still maintain that there is little to be gained and a lot to be lost from introducing a piece of freshly cut wood or sawdust into a melt. At least in yellow brass there is a discussion to be had about the potential reduction of copper oxides but when the discussion moved onto sawdust in aluminum melts I lost interest.....I can see no benefit there whatsoever. Best, Kelly
I live near a large aluminum smelter operation. I toured the plant 30 to 40 years ago. I remember distinctly being intrigued when the company tour guide told about their practice of purchasing large quantities cottonwood saplings of about 1-2 inches in diameter for addition to their pot line melting process. That was long before I ever considered my own small foundry. Detailed reasoning for the addition were not given. Years later I encountered someone whose side hustle it was cutting selling the saplings to Intalco. There must be some benefit at least in the original aluminum smelting process. Denis
I can understand that in processing ore where a large portion of material in process may be something other than the metal, but when you have something refined to the level of even recycled castings let alone specific aluminum alloys, I'd say it's much more likely a step backward, and potentially dangerous, especially for a hobbyist. Just thought a different opinion might be in order lest we start a new trend with folks sticking wet logs in crucibles full of molten metal......heard it on THF .... Best, Kelly
A blacksmith friend mentioned he sort of wants to try making (wrought?) iron by "puddling" some day. From what I was able to discover here and elsewhere online, that involves a reverb furnace and stirring molten metal with long wooden poles too. Sounds exciting and little bit scary! Jeff
Apologies for trimming your post Kelly, according to this paragraph in Wikipedia, you end up with 99% pure copper blister. Poling was used into the 1980's in Australia but now hydrocarbon gas poling which is the modern equivalent is widespread in copper refineries. In some cases it's profitable to electrolytically refine copper as the sludge leftover in the tanks contains gold, platinum and silver in it but mainly so the copper can be used for electrical purposes (oxygen free copper). "Fire refining The blister copper is put into an anode furnace, a furnace that refines the blister copper to anode-grade copper in two stages by removing most of the remaining sulfur and iron, and then removing oxygen introduced during the first stage. This second stage, often referred to as poling is done by blowing natural gas, or some other reducing agent, through the molten copper oxide. When this flame burns green, indicating the copper oxidation spectrum, the oxygen has mostly been burned off. This creates copper at about 99% pure."
That might be a way to line the pot with carbon to improve the electricity flow for the big carbon arc electrode in the middle of the melt until things get hot enough.
It's interesting that the Coppercountry webpage indicates the use of poplar, not particularly sappy as far as I know, and they only mention carbon as the desired product of it. I may slip down that rabbit hole.
Here in Australia, it was fresh cut gumtrees which can have a fair bit of resin, like pines. Edit: I was thinking today of what combustion products come off wood and thought of destructive distillation: heating wood in a sealed container to high temps gives off products like wood alcohol and wood turpentine so you get a significant quantity of hydrocarbons coming off as the wood burns that would reduce the copper oxides back to copper metal just as they do with gases like methane etc. with the modern poling processes.
