Jerrel C. Anderson
The elegantly shaped, but damaged, plummet shown in Figures 1 and 2 was found by me many years ago just east of Chillicothe’s Bridge Street on the Scioto River flood plain. This site is now occupied by a restaurant.
Two very similar hematite plummets were excavated from the Davis Mound in Franklin County (Gehlbach, 2015) and are shown in Figure 3. These plummets were found in association with late archaic burials found in pits below the Adena period Davis Mound. A radiocarbon date of 3,350 years BP was obtained for this late archaic component. The plummet detailed in this article was very likely of the same age.
It is made from hematite, and if it were not damaged, one would think it a homogeneous stone. But it has a yellowish inner core of essentially soft clay or limonite with a harder outer rind showing iron-rich “growth” rings. The perplexing thing is that the inner core exactly matches the contours of the plummet, and it is impossible that the maker of it found a stone already shaped so beautifully as a plummet. The plummet had to have been formed and then somehow the soft inner core formed when iron was leached from it to form the rind of the artifact. Such a process, if natural, would have required extended times in a wet environment and at an enabling pH (acid level).
The damaged top of the plummet is shown close-up in Figures 4 and 5. The groove scar around the top is more apparent in Figure 4 and it appears to have a slight patina on it and perhaps some slight wear from the cord that had resided there. Dark iron-rich accretion rings in the rind are displayed in Figure 5 and they exactly follow the contour of the artifact; this indicates a chemical process of leaching of iron from the core into the outer rind after the artifact was formed. But what is really confounding is that the outer surface of the plummet retains its smooth shape and even much of its polish. The discrete accretion rings indicate several episodes of leaching rather than a slow and steady process.
This artifact was brought to a meeting of the Mound City Chapter, where such legendary luminaries as Alvy McGraw, Tom Porter, Donald McBeth, Bob Biddle, Robert harness, and Norm McKnight, rendered their opinions about what might have happened with this plummet. They had seen similar phenomena with hematite artifacts, such as celts and axeheads. One suggestion was that the ancient native made it from a soft iron-rich stone and then immersed it in hot urine to “harden” it. That would be a wet environment and at a given acid level.
The original stone this artifact was made from was probably a fairly soft iron stone, i.e. a clay or silicate and iron oxide mix, that could be shaped rather easily. Also the high iron content made it heavier than normal silicate stones, and this might have been a factor in the maker’s choice of this type of stone. Many plummets are made from hematite, so heaviness was probably an asset for its use – perhaps as net sinkers or casting net weights?
Obviously there was a chemical change with this artifact, but, strangely, it was a change that did not destroy the surface of any part of the plummet. Was this change deliberately done by the maker by a rapid method? Or was the change accomplished by natural processes that took hundreds or even thousands of years? Or did the change occur during its use, whatever that was?
What is necessary for such a chemical transport of iron oxide is: (1) water and (2) a favorable pH (acidity) level. By acidity, I do not mean extreme acid conditions (pH well below 7), but the acidity level could have been mild; or the conditions could have even been slightly basic (pH slightly higher than 7.0), although this is not probable. Iron oxide, Fe2O3, hematite, is generally in a complex ionic (charged) form with attached water molecules (hydrous condition), and therefore can be vulnerable to chemical transport in conditions favorable for such; for example, wet and mildly basic or especially acidic conditions. The chemistry is complex and does not need to be labored here, but if this artifact was subjected to swampy (wet) conditions and at a pH level conducive to iron movement, then the iron-rich rind and an iron-deficient core would result. And looking at the top of the artifact, where the fractured surface is revealed, we see those iron-rich “growth rings”. This implies separate episodes of iron transport resulting from dry and wet conditions over time.
Robert L. Turner (2006) wrote an article in the Texas Archeological Society Journal in 2006 titled “Hematite Axes of Northeast Texas”, and in that article he treats at length the “exfoliation” of hematite axes: the same phenomenon described herein with the hematite plummet. The hematite axes in Texas were made from a ferruginous sandstone: a homogeneous mixture of sandstone and hematite (iron oxide). These axes exhibited varying degrees of exfoliation where the outer layers of the axes would split off under impact or from natural freeze and thaw cycles, thereby revealing an interior with tree-ring-like layering of iron oxide that mimicked the shape of the axes, much like the situation with the plummet from Chillicothe. Here the axes had undergone this layering process after they were shaped and he considered it an effect of rain water, which is acidic with a pH of 5.5 from carbonic acid (from the carbon dioxide gas dissolved in it). The inner cores of the axes consisted of limonite: a generally yellowish mixture of iron oxides. The rings are called Liesegang rings after a German chemist, R. E. Liesegang (Liesegang, 1896) who observed and reported the repetitive chemical layering phenomenon in sandstones.
Turner relates that a John Gustafson published a paper in 1970 (Gustafson, 1970) about a hematite axehead from northern Alabama that exhibited exfoliation and he enlisted the service of Dr. Frank J. Soday, a chemist, to help in determining what was going on with this axehead. Turner writes that Gustafson’s conclusion, after several theories of what happened were explored, was that the layering-influencing phenomenon remained a mystery!
What about the theory of the Native Americans selecting an iron stone, shaping it into an artifact, and then immersing it in a solution, such as urine, in order to induce the iron transport? Urine is slightly acidic with a pH of about 6.0 and this pH would be perfect for ion transport within the artifact. The question that needs to be asked is: what would such a process do to the surface of the artifact; the only part the maker would have been concerned about. It would not have increased the weight of the object but could have changed the surface hardness and/or color. The object could have been fabricated from the soft and easily worked iron stone and then been subjected to the chemical treatment to harden the surface by enriching it with harder iron-rich ferric oxide. Then it could be smoothed and polished and made more attractive and/or even more serviceable. If the object was an axe head, such a hardening process would be necessary to make it a better, and perhaps a stronger and harder, cutting instrument. This scenario seems rather far-fetched, but it seems to make sense as the object could be carved when in softer condition and then hardened to make it more serviceable and more effectively polished and/or sharpened. A factor in favor of this artificial process is that the groove around the top of the plummet looks to have been carved after the hardening process.
A problem with the immersion method is that the iron would not have to stay in the artifact: it could just dissolve out into the liquid medium and be lost. This artifact looks to have been subjected to several iron transport operations. In other words, it was an episodic process. If they were used as weights for nets and/or hook lines, they could have come loose and become lost on the bottom of sloughs where they would rest for many years under wet and dry conditions, as many sloughs are only covered with water in wet seasons and become dry in drought conditions. Here there could be a natural setting that would lead to episodic leaching of iron oxide from the inner core out into the artifact rind.
After looking at all the evidence, I think this artifact reveals a deliberate process used by the maker many years ago: (1) a soft iron-rich stone was selected, (2) it was carved into shape, (3) it was immersed in a slightly acid solution (urine?) and soaked until saturated, (4) it was then removed from the bath and allowed to dry (baked) in the air and the iron would be transported towards the surface with the evaporating liquid medium, (5) this process was followed several times, and finally (6) it was polished and the groove around the top carved into it. And presto, the maker had an attractive, hardened and heavy plummet to be used for whatever.
In the case of the Texas Axeheads, Turner states that the original stones used by the natives to make their axeheads were homogeneous throughout, i.e. there was no layering in them. Some of the axeheads were made from hematite nodules found in stream beds and here there should have been ample opportunity for weather- and water-induced layering before anyone found them; i.e. natural layer formation. This possible scenario was not covered by Turner. In other words, were these stones not weathered under ideal natural conditions while other such stones found in the unaltered state by the natives were shaped into axes and then mysteriously chemically changed to have outer hard rinds that eventually exfoliated?
This artifact surely raises a lot of questions. However, we must never under-estimate our ancestors; they were inventive and did what they needed to do to survive and even to flourish. This artifact could very well be evidence of chemical invention by ancient Americans.
Gary Argabright informed me about Robert Turner’s article in the Bulletin of the Texas Archeological Society.
Gehlbach, D. R.
2015 “The William H. Davis Mound Examination of 1959”, “Ohio Archaeologist”, Journal of the Archaeological Society of Ohio, Volume 65, No. 1, pages 49 – 51.
Gustafson, J. H.
1970 “An Unusual Grooved Laminar Axe”, Alabama Archaeological Society, XVI, No. 2: 129-133.
Liesegang, R. E.
1896 Naturalwiss. Wochenschr II.
Turner, Robert L.
2006 “Hematite Axes of Northeast Texas”, Bulletin of the Texas Archeological Society, Volume 77, pp 1 – 32.