Hi guys,
I got in a discussion on another site about carbon 14 dating a sword blade. I know you can only carbon date organic matter, but since steel is made with carbon that comes for organic matter we are not sure. Some think that you could at least tell when the wood was cut that was used for the smelting and forging. I would think you would need to know the kind of tree and how it was forged to know the amount of carbon 14 in it when it was made. What’s the straight dope?
No you can’t date the steel, but you might be able to date anything on the handle if it was made of wood or of silk/string. I believe that dating steel/metal is done by the amound of impurities in it, usually the older stuff has more crap in it because of smelting techneiques.
These days, iron refining is done with carbon that comes originally from coal. The carbon-14 clock in that coal started a long, long time ago. By now too much of the carbon-14 has decayed to be able to date the material. If people in the past used some carbon source other than coal, though, it might be possible to carbon-date the steel.
Wrong. Carbon dating can only be done on organic things. The dating process measures when the item stopped being exposed to atmospheric carbon.
If there were wood handles, or something like that, you could date them, as Edward already said. If it was a cooking pot, you could date food remains. Of course, neither of these would tell you when the actual steel was forged, but these types of dates can provide context and help estimate a range of dates that the steel may have been forged between.
Sorry grenadier, I misread the question. After some more thought I can see where you are gong with your question, but I think that the answer is still “No you can’t date it”.
Yes, charcoal is used to turn iron into steel. Charcoal, if you had some, could be dated to when the wood was burnt. The problem is still with the carbon. This site is good for understanding the basics of smelting in the middle ages.
The bolding is mine. The problem that you face is that any carbon is now part of the metal, and IIRC, it is molecular and not big ol’ chunks. Assuming that you could remove the carbon from the steel, the sword would probably be destroyed in the attempt to collect a large enough sample to analyze.
Most of this is by memory, so I emailed some archaeologist friends to ask them about the best way to date steel. I’ll let you know.
Thanks Guys, I’ll put a link on the other forum to this thread.
Carbon-14 dating works because a certain small percentage of carbon atoms are carbon-14 instead of the normal, non-radioactive forms. When living things die, they stop taking up carbon (in any form), but the carbon-14 in their systems gradually decays like any other radioactive atom. The rate of this decay is known, so scientists can compute when something died from what percentage of its carbon-14 has decayed. Inorganic carbon never died, and didn’t take up a constant rate of carbon-14 in life as all living organisms do, and thus can’t be dated this way.
Two hundreth post! Even if it is (ugh) about chemistry.
In theory, you’re friends are right, you could do it. You may have to melt the sword to a puddle and blow oxygen through it to extract all the carbon as carbon dioxide, but you should be able to get enough carbon to perform the measurement (sword steel will be around 0.1-0.8% carbon by weight. So a 5kg sword should give up at least 5g of carbon if you’re careful, and they dated the Turin Shroud with a much smaller sample than that.) In practice this is quite difficult - you’d have to collect a lot of hot gas from your liquid steel and carefully separate out the carbon dioxide.
Steel is made by smelting iron ore (haematite and/or magnetite, Fe[sub]2[/sub]O[sub]3[/sub], and/or Fe[sub]3[/sub]O[sub]4[/sub]) with coke (today) or charcoal (iron-age). If the steel was smelted using coke, this will tell you nothing - coal is too old to date using carbon 14. If the steel was smelted using charcoal (e.g. anglo-saxon, Roman, Japanese samaurai sword) then you’d get the age of the tree which was used to make the charcoal, which is a good estimate for the age of the sword. I’d be interested to know if this is actually done however - totally destructive testing is probably rather frowned upon by archaeologists!
Adam Yax “The problem that you face is that any carbon is now part of the metal, and IIRC, it is molecular and not big ol’ chunks”
That is the problem alright. The carbon exists in the steel as an interstitial solid solution (carbon atoms in the gaps between iron atoms) and as iron carbide, Fe[sub]3[/sub]C. When you heat it, the carbide dissolves and the carbon all goes into solution. Blowing oxygen into molten iron is the current most popular method of reducing the carbon content of blast-furnace iron, but is done on a massive scale. Doing it in a lab and collecting all the exhaust gas would be tricky, although not impossible.
Wrong. A carbon atom is a carbon atom, no matter what its history is. Carbon dating can be done on inorganic substances if the carbon has a recent organic origin. You’re not measuring when the steel was exposed to atmospheric oxygen. The point of carbon dating is to find the ratio of carbon 12 to carbon 14 and determine how much carbon 14 has decayed since the organism that fixed the carbon out of the atmosphere was alive. Steel commonly contains carbon because people who refine steel use reduced carbon to reduce iron oxide to iron. If the carbon they were using was of recent origin, like charcoal, (I don’t know if anyone has ever done that) and if that was the only source of carbon in the steel, then there’s no reason that the isotopic ratio of the carbon in the steel couldn’t be measured and used to determine an age for the tree that the charcoal came from. It wouldn’t matter that the carbon was inorganic if it had a recent organic origin.
Not more than 10 min ago, I was reading in my brand new edition of the American Chemical Society’s "Chemical and Engineering News…Oct 15 p.28.
A research group at Texas A&M are using low pressure, low temperature (1 torr, 150 degrees C)oxygen plasmas to NONDESTRUCTIVELY extract miniscule amounts of carbon (0.1 milligrams)from samples to carbon date them.
Now back to regular programing.