te: Mon, 2 Sep 1996 16:57:35 +0200 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Peter Becker-Heidmann Subject: Re: Univ. Michigan & Wisconsin 14C? Comments: cc: theaton@sunbird.usd.edu In-Reply-To: from "Timothy H. Heaton" at Aug 28, 96 11:00:54 am Content-Type: text The 14C lab of University of does not exist (any more). Probably, David Sewell can find a contact in th old files. WIS Dr. David M. McJunkin Center for Climatic Research University of Wisconsin-Madison 1225 W. Dayton Street Madison, Wisconsin 53706 USA Tel: 608-262-7328; Fax: 608-262-5964 > > I'm trying to track down some information on some old 14C dates mentioned > in the Wisconsin Archaeologist 47(4):219. They are from the *University > of Michigan* (M-1581 to M-1596) and the *University of Wisconsin* (Wis-180 > to Wis-186). I don't know if these labs are still operating or who to > contact. Can anyone give me a lead? Thanks > > Timothy H. Heaton /|Mountains /| theaton@sunbird.usd.edu > Professor of Earth Sciences /::|Deserts /::| Phone: (605) 677-6122 > University of South Dakota /::::|Caves /::::| FAX: (605) 677-6121 > Vermillion, SD 57069 /::::::| /::::::| //www.usd.edu/~theaton > -- Peter Becker-Heidmann Institut fuer Bodenkunde Phone: +49 40 4123 2003 Allende-Platz 2 Fax: +49 40 4123 2024 D-20146 Hamburg E-Mail: PBeckerH@Uni-Hamburg.de GERMANY WWW: http://www.geowiss.uni-hamburg.de/geo/i-boden/tt14c.htm ========================================================================= Date: Sat, 14 Sep 1996 18:29:08 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Jelmer Eerkens Subject: running dates Dear listmembers, I'm a graduate student in archaeology at UCSB working on my PhD dissertation. My research includes working with a previously excavated site from the Owens Valley of California from which I'd like to run radiocarbon dates on some hearths and house floors (large chunks of charcoal were saved in the field). However, I notice that the samples were not put in aluminum foil, and were deposited straight into sandwhich baggies in the field, where they have remained for the last 5+ years. I am not all that knowledgeable about the C14 process, but in my experience I have always put carbon samples into some kind of metal foil, in the field. I assume this is done because plastic, being a petroleum product, can introduce modern carbon into the archaeological sample. The question I have, is how much can/will this affect any radiocarbon dates I run on the archaeological samples, and/or can anyone direct me to some possible references on this subject?? I.e., does storing carbon in plastic baggies have a noticeable effect on any C14 dates? Thanks very much for any help Jelmer Eerkens, University of California, Santa Barbara ========================================================================= Date: Mon, 16 Sep 1996 08:58:04 -0500 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: james burton Subject: C-14 & baggies In-Reply-To: <199609150129.SAA18396@sscf.ucsb.edu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" I have no experience with samples for C-14 from plastic baggies, but I have been looking at organic residues on potsherds. EVERY potsherd that was bagged in plastic has been heavily contaminated with organic pthallates, which are added as 'plasticizers' to organic polymers. I presume the pthallates are derived from coal or oil and are thus dead carbon. How old do you want your sample to be? :> I was warned more than once, however, about using Al foil 'shiny side out' under the argument that Al foil, itself, is sometimes coated with a thin wax layer....this might be an 'urban legend', I don't know (but would like to). == I agree that samples placed in a plastic bag directly might absorb plasticizers from the bag. However, in my opinion the concentrations of these materials is probably not all that high and I do not have any direct information on samples giving an erroneous age as a result of this packing. We have certainly run samples of charcoal directly placed in plastic bags to no apparent ill effect. I would recommend wrapping in AL foil first if only for your own peace of mind. Tim Jull -------------------------------------------------------------- A. J. Timothy Jull tel. (520) 621-6816 NSF Arizona AMS Facility, fax. (520) 621-9619 Physics Building, University of Arizona, Tucson, AZ 85721 University of Arizona AMS Lab Web-Page: http://www.physics.arizona.edu/ams/www1.html ========================================================================= Date: Mon, 16 Sep 1996 10:40:04 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Austin Long Organization: Geosciences / University of Arizona Subject: C-14 and Baggies MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Another argument against baggies is that if a sample is sealed moist, it can become a fungal growth medium. We have noticed an apparent decrease in C-14 age in moist organic samples with visible mycelia. Austin Long ========================================================================= Date: Mon, 16 Sep 1996 11:17:39 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: "William T. Hartwell" Subject: Re: C-14 & baggies Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Here is a response I received from Dr. Herbert Haas, who runs the radiocarbon lab at DRI, in answer to my query regarding plastic baggies: Ted Hartwell Quaternary Sciences Center Desert Research Institute Las Vegas ---------- Forwarded message ---------- Date: Mon, 16 Sep 1996 11:04:52 -0700 (PDT) From: Dr. Herbert Haas To: tedh@spring Subject: Re: C-14 & baggies (fwd) Ted: FRESH ziplock bags, preferably the "freezer" quality, should be OK. They should however not be left lying around in the plain sun, because the heat and the UV can degrade almost any plastic and cause release plasticizer volatiles. Old and recycled bags, often used by archaeologists in countries abroad, are causing this problem too. Aluminum foil should be washed with a solvent, like acetone, petroleum ether or 100 % isopropyl alcohol. Fresh foil is coated with with an vegetable based oil to prevent sticking to the rollers in the manufacturing of the thin foils. Well washed food containers with snap-on lids and film canisters are good containers. DO NOT put paper labels inside, directly in contact with the sample material. This should be evident, but the practice is still widespread! Good luck in collecting more samples! Herbert. ========================================================================= Date: Mon, 16 Sep 1996 16:31:35 -0230 Reply-To: Jun Abrajano Sender: Radiocarbon Mailing List From: Jun Abrajano Subject: Re: C-14 & baggies In-Reply-To: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII If I could just qualify the comments below. Although I am not a 14C-expert, I do a lot of trace organic work. I agree with the two main points below: (1) phthalate plasticizers are contributed by plastic bags, and (2) aluminum foils need solvent washing to rid it of trace organic contaminants. I'd just add that we know from experience that even ziplock bags stored cool (e.g., freezers) will introduce phthalates anyway. The question in my mind really is the 14C nature of this contaminant, and whether this matters (mass balance-wise). I don't know about "Tupper-Ware" type containers or film canisters. Solvent washed Al-foil is the option preferred for trace organic work. > FRESH ziplock bags, preferably the "freezer" quality, should be OK. > They should however not be left lying around in the plain sun, because > the heat and the UV can degrade almost any plastic and cause release > plasticizer volatiles. Old and recycled bags, often used by archaeologists > in countries abroad, are causing this problem too. > > Aluminum foil should be washed with a solvent, like acetone, petroleum > ether or 100 % isopropyl alcohol. Fresh foil is coated with with an > vegetable based oil to prevent sticking to the rollers in the manufacturing > of the thin foils. > > Well washed food containers with snap-on lids and film canisters are > good containers. DO NOT put paper labels inside, directly in contact > with the sample material. This should be evident, but the practice is > still widespread! > > Good luck in collecting more samples! > Herbert. > ========================================================================= Date: Tue, 17 Sep 1996 08:40:34 +1200 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: "SPARKS, RODGER" Subject: C14 & baggies This seems to be one of those situations that crop up from time to time where "everybody knows" that this or that will happen if some procedure is followed or ignored, but in fact there is little or no direct evidence one way or the other. It is not difficult to do some order of magnitude calculations to see what kind of effects can occur. For example, a sample with "true" radiocarbon age 1800 BP will have its apparent age shifted by about 80 years if contaminated by 1% dead carbon. So, if you place your 100 mg (carbon) sample in a plastic bag, how likely is it that the sample will incorporate 1 mg carbon from the bag when you take it out? Plastic bags are a convenient way of packing and sending samples. Perhaps someone should do a systematic study of contamination effects from different types of plastic under different conditions to settle this question once and for all, so we can stop being frightened by anecdotal evidence relayed second hand. ========================================================================= Date: Mon, 16 Sep 1996 17:54:51 -0400 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Greg Laden Organization: Harvard Faculty of Arts and Sciences Subject: Re: C-14 & baggies MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit I am confused by some of this commentary.. First, wouldnt' a plastic bag make a date too young instead of too old (i.e., if you accidently processed the entire bag along with the sample, because it is mate out of petro.lium product? Also, on Al foil...I think that one side (the dull side) of foil is coated with oil. I'd avoid putting that side against the sample. It must be true that for most samples, there are carbon-containing bits of yech and stuff from the sediments, including living microbes and old bits, attached to the sample that would outweight any contamination from plastic bags. The samples have to be very well cleaned (chemically) or they are not worth running. A plastic bag has got to be the smallest problem to worry about, yes?? Timothy Jull wrote: > > I can add some comments about the baggie question. We usually recommend > that samples are wrapped in Al foil first. This is because Al foil is the > cleanest packing material one can easily obtain. -- Greg Laden Department of Anthropology Harvard University gladen@fas.harvard.edu http://www.fas.harvard.edu/~gladen/ ========================================================================= Date: Mon, 16 Sep 1996 20:30:02 -0500 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: "Kevin E. Smith" Subject: Re: C14 & baggies In-Reply-To: <9609170841.423dbb51.GNS@wpo.gns.cri.nz> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII I think Rodger Sparks makes an excellent point concerning a need to develop and distribute some quantified (and supported) information to the archaeological community about the effects of "baggies" or other packaging materials on C14 samples. Archaeologists have a remarkably detailed set of mythologies concerning sample acquisition, storage, and so on. Over the past 5-6 years, I have obtained C14 dates on a number of samples that have been curated for 15-20+ years in various types of materials (plastics, paper, aluminum foil). Relative to the current discussion, several specific samples come to mind. One was a charred post fragment from a residential structure that must date at the widest possible interval between A.D. 1050 and 1450 (based on over 100 determinations from sites in the vicinity with similar artifact assemblages). The log was stored for about 20 years wrapped in a big sheet of cheap industrial grade plastic wrap which had essentially turned into crumbly plastic garbage by the time I obtained the sample. I submitted a sample from the outer rings of the log (in direct contact with the deteriorating plastic) and one removing the outer three or four rings. Both came back as essentially the same date, and both matched closely the expected dates in comparison to samples obtained from the same site a decade later that were stored in aluminum foil (admittedly, I don't recall whether the shiny side of the foil was in or out). I do recall that the reason I submitted the second sample was a concern over possible contamination by the plastic wrap, but this still falls into the anecdotal range. In my personal experience with at least a couple of hundred C14 dates (and attempts to deal with hundreds of others outside my personal experience!), the greater problems are not with packaging materials, but more with the certainty of context and the nature of the sample (for example, consolidated fragments vs. large singular pieces). There may be contaminant problems with "baggies," aluminum foil oil or wax, and others, but I have yet to see any quantification of these factors (either in my returned dates or in other literature). Best wishes, Kevin E. Smith kesmith@frank.mtsu.edu ========================================================================= Date: Mon, 16 Sep 1996 20:58:39 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Dick Meehan Subject: Re: C14 & baggies In-Reply-To: <9609170841.423dbb51.GNS@wpo.gns.cri.nz> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Surely the plastic bag contamination problem has some legitimate scientific answer, but it is much more interesting as a religious problem. The religion I have in mind is so-called secular science, which of course is often religion in disguise, one commandment of which is "Thou shalt not suffer the nasty modern world to interfere with our pleasing belief in the pristine ancient world." In other words, no plastic in the Garden of Eden, please. Hard-nosed physicists will honestly scoff at this, but those who are attempting to reach an accomodation with the so-called social sciences will recognize that certain delicate accomodations are necessary. Many years ago I was trained as a Catholic acolyte and I know all about what it takes to decontaminate sacred objects. It will be interesting to see whether scientists, after doing the obvious weights and measures sort of evaluation of this problem -- a straightforward bit of fundamentals, one would think -- will eventually develop appropriate rituals to assure the sanctity of their results. Dick Meehan ========================================================================= Date: Tue, 17 Sep 1996 07:58:25 PDT Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: "Dr. Robert M. Kalin" Subject: Re: C-14 and Baggies MIME-Version: 1.0 Content-Type: TEXT/PLAIN; CHARSET=US-ASCII Dear Forum, A mass balance calculation for you.... Sample age: 75% modern = 2311 yBP 1 gram of carbon counted by conventional means Contaminate this sample with 'baggie' 10 milligrams of plastic (0 PMC) = 2392 yBP (81 yrs error) 1% of total sample 50 milligrams of plastic (0 PCM) = 2723 yBP (412 yrs error) 5% of total sample Please note that 10 milligrams of plastic baggie is a significant contamination from degradation of the original plastic and I suspect this much degradation of a baggie would be quite noticable. I would tend to side with Austin Long here, a more probable source of modern contamination is the growth of algea, fungi or other microorganisms on a wet sample while in the baggie (or before collection). When collecting the sample, the sample provinence is very important to the laboratory when choosing the pretreatment method. If a sample has potential contamination from fungal or algeal growth, the laboratory can use ultrasonic techniques to help dislodge the modern contaminants from the original 'sample' material. Bob Kalin ========================================================================= Date: Tue, 17 Sep 1996 09:16:07 -0700 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: Timothy Jull Subject: Re: C-14 & baggies In-Reply-To: <323DCCAB.357F@fas.harvard.edu> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Greg Laden is quite correct that there are many other more serious sources of contamination. Plasticizers can be detected in minute quantities which do not affect a 14C age. More serious forms of contamination are removed by looking at the sample under a microscope and chemical pretreatment. Here are some things we have seen in our lab and removed: 1. bits of more recent material falling into your sample during collection. 2. bits of archaeologist (e.g. hair) 3. insects (living and dead) 4. humic and fulvic acids from the soil which are removed chemically 5. glues of various kinds 6. Yak butter (on silks), food, etc. 7. fungal growth on samples of wet sediment and charcoal which were not dried by the sender. Clearly, what one dates is the important question. The sample must be clean and represent what you are attempting to date. Tim Jull -------------------------------------------------------------- A. J. Timothy Jull tel. (520) 621-6816 NSF Arizona AMS Facility, fax. (520) 621-9619 Physics Building, University of Arizona, Tucson, AZ 85721 University of Arizona AMS Lab Web-Page: http://www.physics.arizona.edu/ams/www1.html ========================================================================= Date: Fri, 27 Sep 1996 12:31:07 +1200 Reply-To: Radiocarbon Mailing List Sender: Radiocarbon Mailing List From: "SPARKS, RODGER" Subject: Athol Rafter It is with sadness that I have to announce that Dr Athol Rafter passed away at 10pm on September 26, after a long illness. Athol was one of the pioneers of radiocarbon dating. The laboratory he established at Lower Hutt, New Zealand, was among the first to use gas counting after Willard Libby demonstrated that carbon dating was practical. Athol's foresight resulted in 14C monitoring of southern hemisphere atmosphere and ocean water beginning before the major perturbation due to nuclear weapons testing swamped the natural background signal. Athol took a lively interest in the development of accelerator mass spectrometry as it revolutionised the field of radiocarbon, to which he had contributed so much. The Lower Hutt laboratory that grew out of his efforts is proud to bear his name as the Rafter Radiocarbon Laboratory.