Last night I was in the Chaldon quarries and noticed lamp/candle soot on the roof, of which there is loads and we have never really given it much thought as being useful for dating.

But the soot marks were very likely from candles made of tallow, and as such might be useful for carbon14 dating. Is anyone aware of using such small quantities of carbon as you get from a soot mark this way?

It would be a very useful thing to do as these workings are so old that there is very little in the way of dateable artefacts such as clay pipes. The great thing about soot marks is that they have not been moved about as loose artefacts might be, and can therefore be directly associated with the place they are found. Also, unlike timber which might be some years old before it is used underground, the tallow candle would have been derived from an animal that had been alive only shortly before being made into candles.

So, two questions - has anyone heard of soot marks being used for dating, and how small a sample can be used reliably these days?

Do do small samples, you need Mass Spec, which quite a few uni departments have.

It would make a bloody good project for some Analytical Chemistry students to investigate. Find which uni's do AC and then email the chief and they would be pretty stoked to do such a thing. You would be armed with a nice report with a detailed write up of the limitations/discussion.

Our nearest unis are at Brighton, Guildford and in London. So a good chance! Thanks for the suggestion. Even better if there are also departments that have an interest in medieval archaeology.

It's certainly been done. See Carbon Dating Prehistoric Soot from Salts Cave, Kentucky. http://www.jstor.org/pss/278384 .
Unfortunately the full article isn't available online.

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Considering that article was written in '62, the accuracy isn't that bad (bearing in mind that the older you get, the smaller the 14C peak is and thus more difficult to resolve).

Modern mass spec is a whole lot more user friendly and the output pretty darn good.

Just out of interest.....what is the composition of the wall rock?

Inorganic carbonate has pretty much no C14 in it, so if there was any limestone/etc contamination, you could perhaps have found the worlds oldest candles :lol:

You can get away with milligrams of material for AMS C-14 and it's not massively expensive, I think it's about a hundred quid for a one-off at one of the labs that does this sort of thing commercially - have a look online for UK testing labs and see what they can do for you. You need to clean the collecting and storing equipment carefully to remove any possible contaminants, but the professionals will be able to advise you on that.

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That is a problem, Stuey. The roof is a calcareous sandstone / siliceous limestone depending on how you look at it! It's a sort of immature chert with carbonate content. The soot would have to be separated from the rock without contaminating the sample with organic matter. The antiquity of the soot in some places is in little doubt because it has a thin flowstone layer over it, but that just compounds the problem of carbonates being present. It was finding soot-coloured flakes of flowstone on the floor where it has peeled off the roof that started this train of thought.

If I recall correctly...

There is an issue with Carbon 14 dating in that it's pretty useful for dating stuff a long time ago, but that it's not much use for more recent events.

The half-life of Carbon-14 is somewhere around 5,700 years, so 150 years ago is around 2.6% of a half-life, thus it's difficult to gauge the decay with any accuracy over such a short period.

Similarly, I doubt it's going to give you the sort of accuracy you'd need - 10 years either way works out at about 0.17% of a half life, so even if there's a leeway of 1% that would relate to 57 years either way, which may not be much use!

A little bit of research suggests that carbon dating is generally only considered useful for samples over 300 years old. I can't quite see why, though!

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300 years? Perfect! Most of the undated stuff is at least 1600 or earlier, and possibly back to the 12th century.

I think otherwise. The analytical equipment available has come on seriously in the last few decades. The relative abundances would be very accurate indeed. I imagine you'd get well within the 100 year mark accuracy wise. Coupled with the fact that you could accurately calibrate the machine and you'd be laughing.

Of course, the mass spec machine I used to use was pretty lo-fi. When you're dealing with a seriously expensive machine, the output will be unbelievably accurate.

As far as the carbonate is concerned, if you could be sure it was free from organic matter (ie growing stuff) you'd just munch the whole lot up, clean it with acid and then wash with water. That would get rid of the inorganic stuff.

The more I think about it, the more I think it's totally achievable.

As I said, this would be a bloody good project as it's got a number of snags/limitations which would necessitate careful thought and a methodology for success.

I reckon you could get a university on board for some muggins to do a 3rd year project on. :thumbup:

I think the main problem would be the method uses cross referencing of hard data from the same area / time / etc.

I doubt that the area, in terms of climate, vegetation, rainfall, etc, would change much over a period of say.. a hundred years. So, as it's already been said, you arn't going to get a very accurate answer.
Unless, something major happened, like a flood or drought, at the same time the candle was made.

If the candle was made from living stuff, both wick and wax, it would have a C14 content which would decay over time. You measure with the best mass spec money can buy and you get your answer.

No problem whatsoever.

There is nothing else required in the methodology to gain an answer.

Unless you are assuming that there are fluctuations in the C14 production/absorption.....???

My cousin Grenville Holland was head of geology at Durham (think he's retired now) but was a leader in the ICP MS field for years - might be worth contacting Durham - I know they have a very heavy duty MS setup, and were virtually a product development arm of Perkin Elmer.

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If the candle was made from living stuff, both wick and wax, it would have a C14 content which would decay over time. You measure with the best mass spec money can buy and you get your answer.

No problem whatsoever.

There is nothing else required in the methodology to gain an answer.

Unless you are assuming that there are fluctuations in the C14 production/absorption.....???

The method uses cross referrencing of existing data from the same time / area to calculate the date of said object.

If one has 3 candles - one from 1800 and one from 1912, and also the candle in question. One would use the carbon14 dating method on the candles which one knows the year of and uses that data (and other data such as vegetation state, rainfall, average temperatures, etc) to work out the date when the 3rd candle is from.
There isn't an instrument that you put something in and it comes up on a computer screen saying "this is from 1642".

All organic carbon surely originated from carbon dioxide converted to sugars etc by plants? Then eaten by animals? The amount of C14 in atmospheric carbon dioxide remained pretty constant until we started burning loads of fossil fuels.

So, the ratio of C14 to C12 in pre-industrial organic matter is quite predictable, and the amount lessens with age according to the fundamental rules governing radioactive decay (half life calculations). The ratio of C14/C12 in any living matter will reflect pretty much the ratio in the atmosphere surely. Once something dies, and the carbon content of the body is not replenished, the half life decay of the C14 will slowly reduce the ratio of C14 in the organic matter. So it matters not whether it is a piece of wood, a piece of leather, or some tallow, or even the soot created by burning that material. The soot created by burning the tallow ought to reflect in its composition the C14 content of the stuff that was burnt, and be decreased according to the same half life rule.

Its a long time since I did this at school, so I might have got something wrong.

There isn't an instrument that you put something in and it comes up on a computer screen saying "this is from 1642".

You whack the shizzle in the thingy, press go and then it provides you with a load of graphy stuff a few minutes later.

You ignore everything apart from the tabley thing on the printout and then divide the 2 numbers and compare the result with the decay curve of C14, looking at the difference in your starting point (somewhere along the curve) and your end point (somewhere else). Rather than cocking about with graphs, it's probably better to solve a simple equation.

Put it this way, if they haven't got a mass spec program which hasn't got a carbon dating function, I would quite happily stick a biro up my *******. 😮

oi fink ee be right, Stuey...

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All organic carbon surely originated from carbon dioxide converted to sugars etc by plants? Then eaten by animals? The amount of C14 in atmospheric carbon dioxide remained pretty constant until we started burning loads of fossil fuels.

So, the ratio of C14 to C12 in pre-industrial organic matter is quite predictable, and the amount lessens with age according to the fundamental rules governing radioactive decay (half life calculations). The ratio of C14/C12 in any living matter will reflect pretty much the ratio in the atmosphere surely. Once something dies, and the carbon content of the body is not replenished, the half life decay of the C14 will slowly reduce the ratio of C14 in the organic matter. So it matters not whether it is a piece of wood, a piece of leather, or some tallow, or even the soot created by burning that material. The soot created by burning the tallow ought to reflect in its composition the C14 content of the stuff that was burnt, and be decreased according to the same half life rule.

Its a long time since I did this at school, so I might have got something wrong.

I agree with what you are saying, sounds fairly concrete. My point was, as you say, that the carbon levels in living matter is in direct relation to the atmosphere at the time. The way to get a more precise date of the candle would be to cross referrence the carbon14 data with other carbon14 data from the area in which one knows the date of, most usually Dendrochronology.

Dendrochronology would be great except that almost all the timber props in the workings are now what on the Thursday trip I termed "air props". There is a stain on the roof, a pile of dust on the floor, and air in between. :lol:

Can you not assume the level of C14 in the air to be pretty static? Surely, there will be a variation due most significantly to the sunspot cycles. As "stuff" is often alive for a while.... you'd imagine it to average out. I don't imagine milankovitch cycles would be that significant, but as they are cyclic, they could be applied over the data?

I'm genuinely interested in whether the C14 level in the atmosphere varies significantly. I can't see that it does that much. Otherwise we would see significant alterations in the overall climate. Apart from the little ice age, etc. The total solar irradience has been pretty similar for a while....including the levels of CO2 in the atmosphere.

I can see the point of checking against known samples, but surely you can "assume" the To ratio pretty darn accurately and apply your curve to this.

I'm really interested in this as I just assumed that C14 was "may as well say" static. 🙂