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archaeomagnetic dating

SYNONYM: archaeomagnetic intensity dating, archaeomagnetism, palaeointensity dating, archaeomagnetic age determination
CATEGORY: technique
DEFINITION: A chronometric method used to date objects containing magnetic materials -- especially for buried undisturbed features such as pottery kilns, earthen fireplaces, and brick walls -- which can be compared to known schedules of past magnetic alignments within a region and fluctuations in the earth's magnetic field. Clay and rocks contain magnetic minerals and when heated above a certain temperature, the magnetism is destroyed. Upon cooling, the magnetism returns, taking on the direction and strength of the magnetic field in which the object is lying. Therefore, pottery which is baked in effect fossilizes" the Earth's magnetic field as it was the moment of their last cooling (their archaeomagnetism or remanent magnetism). In areas where variations in the Earth's magnetic field are known it is possible to date a pottery sample on a curve. This method yields an absolute date within about 50 years."

electromagnetic spectrum

CATEGORY: technique
DEFINITION: The spectrum of frequencies of electromagnetic radiation, with light being the visible part of the spectrum and heat another. There are parts of the spectrum which are not detectable by human senses but spectrophotometers can monitor all areas of the spectrum. Data can be analyzed and used to find and understand structures.

electromagnetic surveying

SYNONYM: electromagnetic prospecting
CATEGORY: technique
DEFINITION: A geophysical surveying method used to locate archaeological features and differences in sediment or soil textures. A pulsed induction meter or soil conductivity meter generate electromagnetic waves at the surface of the earth, penetrating it and inducing currents in conducting ore bodies, thereby generating new waves that are detected by instruments at the surface or by a receiving coil lowered into a borehole. This technique only works at a very shallow level, and no electromagnetic instrument is as accurate as the resistivity meter or a proton magnetometer.

geomagnetic reversals

CATEGORY: term
DEFINITION: An alternation of the Earth's magnetic polarity in geologic time. It is an aspect of archaeomagnetism especially relevant to the dating of the Lower Paleolithic, involving complete reversals in the earth's magnetic field.

geomagnetic surveying

CATEGORY: technique
DEFINITION: A method of remote sensing that uses deviations in the earth's gravitational field to locate archaeological deposits.

geomagnetism

SYNONYM: geomagnetic sensing
CATEGORY: related field
DEFINITION: The study of the source, configuration, and changes in the Earth's magnetic field and the study and interpretation of the remanent magnetism in rocks induced by the Earth's magnetic field when the rocks were formed (paleomagnetism). The geological variant of archaeomagnetism.

magnetic

CATEGORY: term
DEFINITION: Of or pertaining to magnetism, the ability to be magnetized or affected by a magnet, or relating to the earth's magnetic field. Magnetism is a class of physical phenomena associated with the motion of charge, the attraction for iron observed in lodestone and a magnet. It is associated with moving electricity, exhibited by electric currents, and characterized by fields of force. It can be an electric current in a conductor or charged particles moving through space, or it can be the motion of an electron in atomic orbit.

magnetic dating

SYNONYM: paleomagnetic dating
CATEGORY: technique
DEFINITION: Any theoretically chronometric dating technique which uses the thermo-remanent magnetism of certain types of archaeological material. These methods use the known changes have taken place in the direction and intensity of the earth's magnetic field. Magnetic minerals present in clay and rocks each have its own magnetic orientation. When heated to the so-called blocking temperature, the original magnetic orientation of the particles is destroyed, and they will take on the orientation of the earth's magnetic field in a fixed alignment -- which does not alter after cooling. These methods are most suitable for kilns and hearths. Once the direction of the archaeological sample has been determined, it may be possible to date it by fitting it to the secular variation curve established for the local area. There is no universal curve, since not only the earth's main field varies, but there are also local disturbances. Since the dating of the curve has to be constructed through independent dating techniques, and these are not available for every area, there are not established curves for every region. As a dating technique, it is strictly limited to those areas where dated curves have been established. A more recent dating technique using thermo-remanent magnetism is palaeointensity dating (archaeomagnetic intensity dating). The principle is that the thermo-remanent magnetism in burnt clay is proportional to the intensity of the magnetic field acting on the clay as it cools down. The measurement of its intensity, and a comparison with the intensity revealed by reheating in today's magnetic field, gives a ratio for the past and present fields which can be used to establish a curve of variation in the earth's magnetic field intensity. The method promises to be useful since direction in situ is not required and it can therefore be used for pottery and other artifacts as well as hearths and kilns.

magnetic reversals

CATEGORY: technique
DEFINITION: A change in the magnetic direction of the Earth. It was discovered that volcanic lava flows, which like kilns and fired clay record the magnetism at the time they were hot, retained measurable magnetization in a reversed direction. Over the last 4 million years, magnetic direction changed at least 10 times. It switched to normal, as we know it, about 700,000 years ago. The direction of the dipole component reverses, on an average, about every 300,000 to 1,000,000 years. This reversal is very sudden on a geologic time scale, apparently taking about 5,000 years. The time between reversals is highly variable, sometimes occurring in less than 40,000 years and at other times remaining steady for as long as 35,000,000 years. No regularities or periodicities have yet been discovered in the pattern of reversals. A long interval of one polarity may be followed by a short interval of opposite polarity. These reversals have proved an important dating aid to archaeology.

magnetic surveying

SYNONYM: electromagnetic surveying
CATEGORY: technique
DEFINITION: A technique for the location of archaeological features adapted from techniques used in geological surveying. It is based on the fact that features with thermo-remanent magnetism, like hearths or kilns, or features with a high humus content, like pits or ditches, and iron objects, distort the earth's magnetic field from the normal. Instruments such as the proton magnetometer or the differential fluxgate gradiometer are used to measure those disturbances, and by plotting the results, a map of the features can be built. The ways in which the different types of feature distort the magnetic field vary, though they can all be picked up on the same instrument. Hematite or magnetic, present in most clays, have a small magnetic effect when unburnt, since the grains point in random directions and cancel each other out. Once heated to about 700? C or more, the grains line up, increasing the magnetic effect and causing an anomaly in the magnetic field. This thermo-remanent magnetism is also the basis for magnetic dating. The presence of modern iron as in wire fences can cause problems with this technique of location; if the area to be surveyed is clearly crossed with power lines or fenced with iron posts, a resistivity survey may be more suitable. The method of surveying used requires a grid to be measured out on the site and readings to be taken at regular intervals. The nature of the site may prevent such a grid being laid out, for instance if it is heavily wooded, and magnetic survey may not be possible on these sites. It is one of the most commonly used geophysical surveying methods.

magnetic susceptibility

CATEGORY: geology
DEFINITION: A property of soil and sediment, measured as a ratio of intensity of magnetization of the material to the strength of an applied magnetic field. Topsoil often has a somewhat enhanced 'magnetic susceptibility' due to magnetic minerals in the material, especially compared with the subsoil. The filling of a ditch or a pit has greater susceptibility than the surrounding area because of higher humus content and perhaps the presence of burnt occupation material. On the basis that contrast between feature and surroundings locates the features, walls, and other stone settings can also be located since they have less susceptibility than the area around them, i.e. they exhibit a reverse anomaly.

magnetite

SYNONYM: lodestone, magnetic iron ore
CATEGORY: geology
DEFINITION: A strongly magnetic form of iron ore, a major constituent of magnetitite and a common accessory mineral in igneous rocks. In the Mesoamerican region, magnetite was commonly mined and polished to make mirrors and compasses. It frequently has distinct north and south poles, and has been known for this property at least since 500 BC.

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basalt

CATEGORY: geology
DEFINITION: A type of very hard, dark, dense rock, igneous in origin, composed of augite or hornblende containing titaniferous magnetic iron and crystals of feldspar. It often lies in columnar strata, as at the Giant's Causeway in Ireland and Fingal's Cave in the Hebrides. It is greenish- or brownish-black and much like lava in appearance. It is also abundant in Egypt and Greece.

bearings

CATEGORY: measure
DEFINITION: A direction or relative position; a horizontal direction expressed in degrees east or west of a true or magnetic north or south direction.

bleeper

CATEGORY: tool
DEFINITION: A surveying instrument that is a type of proton gradiometer, working on the same principle as the magnetometer. When two detector bottles are used, one near ground level and one about 2 m above, small magnetic anomalies underground affect the lower, nearer, bottle more strongly than the upper. The signals from the two get out of step, and their sound signal is broken into a series of 'bleeps'. It is unaffected by large scale disturbance, an advantage over the magnetometer, and is much simpler, cheaper, and more portable than either magnetometer or gradiometer.

caesium magnetometer

CATEGORY: tool
DEFINITION: A highly sensitive portable magnetometer that can detect minute magnetic variations, down to about one millionth of the earth's magnetic field.

cesium magnetometer

CATEGORY: tool
DEFINITION: A measurement tool used to detect large structures underground and their magnetic fluctuations by measuring the effects of transitions between atomic energy levels. It is considered more efficient than a proton magnetometer, which does the same thing.

declination

CATEGORY: term
DEFINITION: The difference between true and magnetic north. In astronomy, the angular distance of a body north or south of the celestial equator.

differential fluxgate gradiometer

SYNONYM: fluxgate gradiometer, differential fluxgate magnetometer, magnetometer
CATEGORY: tool
DEFINITION: A magnetic surveying instrument used in subsurface detection that records changes in the intensity of a magnetic field. Readings can be obtained continually rather than as individual spot measurements of a proton magnetometer. However, it is an expensive alternative to the proton gradiometer. Its electronics involve two detectors with mu-metal strips of a staff which is carried vertically; an initial pure sine-wave voltage is applied, and the difference in intensities observed between the two detectors corresponds to disturbance in the magnetic field cause by baked clay or buried features. These differences are displayed on the instrument's meter.

floating chronology

CATEGORY: chronology
DEFINITION: A chronometrically dated chronology which is not yet tied in to calendar years. A floating chronology is a decipherable record of time that was terminated long ago. The most common floating chronologies occur in dendrochronology where climate affects the growth of rings and sequences are local. Local sequences cannot always be tied to the master sequences established in certain areas from the present day back into prehistory, and therefore the local sequences will 'float' until some link with a known historical date is found. Similarly, in magnetic dating many of the sequences will float until some independently dated sites can be entered on the curve. The term is also used in reference to varve chronologies.

fluxgate gradiometer

CATEGORY: tool
DEFINITION: A magnetometer using two sensors in a light, self-contained instrument which produces a continous output and records differences in magnetic intensities on a meter.

geophysical prospecting

SYNONYM: geophysical survey
CATEGORY: technique
DEFINITION: The location and recording of buried sites by detecting variations in the magnetic properties or resistance to an electrical current of the soil. Many archaeological surveying techniques designed to identify features without excavation use instruments that measure physical properties of surface materials.

gradiometer

SYNONYM: proton gradiometer, fluxgate gradiometer, differential fluxgate gradiometer
CATEGORY: tool
DEFINITION: A geophysical device used to conduct surveys by measuring the gradient in a magnetic or gravitational field. This instrument is used to identify shallowly buried features and structures.

grid amplitude

CATEGORY: technique
DEFINITION: A method of defining the location of features and artifacts on a site by plotting from a reference point oriented to magnetic north or some other known point. Meridian lines run north-south and baselines run east-west on a grid square.

hearth

CATEGORY: feature
DEFINITION: Any place where a pit was dug and a fire built, sometimes identified by charcoal, baked earth, ash, discoloration, or an outline of stones or clay footing. The site of an open domestic fire might have served as kiln or oven. Hearths often appear in one layer of soil after another as an archaeologist digs down through a site, and they are an indication of a succession of camps or habitations. Charcoal from a hearth can be dated by the radiocarbon method. Baked clay in a hearth can be dated by the palaeomagnetic method. Burnt earthen rims may provide oxidized material for archaeomagnetic dating. The hearth is often centrally located and has a variety of shapes and sizes.

instrument anomaly

CATEGORY: technique
DEFINITION: Any change in soil resistivity to an induced electric current or variations in the magnetic characteristics of soil due to human activities, such as pit or trench digging, wall construction, and fire.

iron

CATEGORY: geology
DEFINITION: A ductile, malleable, magnetic metallic element, used to make artifacts of both practical and decorative function. Its oxide form, hematite, is found naturally and the technique of ironworking was mastered around 1500 BC by the Hittites. Iron began to spread and replace bronze for man's basic tools and weapons -- the start of the Iron Age. Early in the 1st millennium BC, iron industries were established in Greece and Italy, and by 500 BC, iron had replaced bronze for the manufacture of tools and weapons throughout Europe. The pre-Columbian New World, however, did not develop iron technology. Iron smelting is more complicated than for copper or tin, since the first smelt gives only slaggy lumps, the bloom. Hammering at red heat is then required to expel stone fragments and combine carbon with the iron to make in effect a steel; the resulting metal is far superior to copper or tin. The two basic methods of working it are by forging -- hammering into shape at red heat -- and casting. The Chinese used the latter method as early as the 5th century BC, but it was not employed in Europe until the Middle Ages. The first evidence of iron smelting in Egypt dates to the 6th century BC. Large-scale steel manufacture depends on the production of cast iron, which in Europe dates only from the 14th century AD. The West did not enter the 'Age of Steel' until the 19th century with the invention of the Bessemer and Siemens processes, which are industrial processes for obtaining liquid metal of any desired carbon content by the decarburization of cast iron. Steel was made in China within a few centuries of the first known use of smelted iron. In principle, modern techniques descended from China's casting techniques.

magnetometer

SYNONYM: proton magnetometer
CATEGORY: tool
DEFINITION: A geophysical instrument that measures the intensity and sometimes direction of the Earth's magnetic field. It is used in electromagnetic surveying to identify changes in the field within soil or sediment that might be caused by subsurface features, hearths, kilns, or metal artifacts. When a current is passed through a coil in a bottle of water or alcohol the protons of the hydrogen atoms align themselves to its magnetic field. When the current is cut off, the protons realign themselves according to the earth's field, its strength being indicated by the frequency of their gyration on realignment. This sets up a weak current which is transmitted back from the bottle to the instrument and there registered on dials. The resulting figures are plotted to reveal anomalies in field strength -- usually due to buried iron, kilns, hearths, or to pits or ditches. These features can thus be rapidly located without disturbance of the ground, and excavation can be directed to the most promising areas. Magnetrometry is the use of a magnetometer for mapping subsurface anomalies. There are a number of designs, but two are particularly widely used. The proton magnetometer makes an absolute measurement of field strength, but is intermittent in operation: each reading is initiated by the push of a button, and takes some seconds to appear on the display of the instrument. Fluxgate magnetometers work on a different principle, and give a continuous reading, which makes surveying less time-consuming. Most fluxgate machines do not however measure field strength directly, but rather are gradiometers, measuring the vertical gradient of the earth's' magnetic field, i.e. how fast the field strength changes with vertical distance from the earth's magnetic field Gradient measurements can also be used in archaeological surveys and have an advantage over absolute measurements. The earth's field strength varies continuously during the day at any one location. Absolute measurements taken at different times have to be calibrated for this effect if they are to be comparable. Gradient measurements are not affected by this diurnal drift in field strength, and so do not need to be calibrated. Proton gradiometers are also available. The fluxgate, differential fluxgate, and proton gradiometer take continuous measurements of relative vertical change in the intensity of field strength.

magnetometry

CATEGORY: technique
DEFINITION: Detecting buried remains through magnetic variations between them and the surrounding soil.

metal detector

CATEGORY: tool
DEFINITION: A geophysical instrument used in electromagnetic surveying to locate metal on the surface, hidden under vegetation, or shallowly buried. Some metal detectors can be programmed to detect only artifacts of a certain alloy.

Omo

CATEGORY: site
DEFINITION: A river basin in Ethiopia north of Lake Turkana, where fragmentary remains of Australopithecus and early Homo have been found. The same deposits have produced flakes of imported quartz, 2.4-2 million years, the oldest securely dated artifacts. The site is of outstanding importance as a basis for dating other sites throughout Africa, because its time-scale is unusually well fixed by palaeomagnetic studies, potassium argon dates, and faunal comparisons.

paleomagnetism

SYNONYM: palaeomagnetism, remanent magnetism; paleo-magnetism, palaeo-magnetism; archaeomagnetism
CATEGORY: technique
DEFINITION: The magnetic polarization acquired by the minerals in a rock at the time the rock was deposited or solidified. The permanent magnetism in rocks, resulting from the orientation of the Earth's magnetic field at the time of rock formation in a past geological age. It is the source of information for the paleomagnetic studies of polar wandering and continental drift. The field of paleomagnetism involves techniques for determining the age of rocks by analyzing the magnetic field polarity of certain minerals in the rock and its importance in archaeology lies in its use as a dating method. The ancient orientation and intensity of the earth's magnetic field is preserved by the magnetization of iron oxides in rocks and sediments and archaeological materials (archaeomagnetism). Ancient direction and intensity of the earth's magnetic field may be preserved in three ways: a) thermoremanet magnetism (T.R.M.) works through the alignment of the magnetic domains within iron minerals when heated to above the Curie point and subsequently cooling, b) detrital remanent magnetism works through the alignment of clay particles sinking down slowly through still lake or deep ocean water. A block of sediment is magnetized in the direction of the earth's field at the time when it was deposited., and c) sun-dried bricks as the bricks become magnetized in the current direction and intensity of the earth's field. Using igneous rocks, independently dated by potassium/argon, and kilns, hearths, pots etc. dated archaeologically, it has been possible to reconstruct something of the history of the earth's magnetic field. Palaeomagnetism proper is done by studying reversals in the magnetic field of the Earth, the youngest reversal dating to 700,000 bp. Measurement of the declination and inclination of the magnetic poles as it affects materials of different ages can be used to build regional chronologies. Palaeomagnetic dating has also been successfully applied to lacustrine deposits, deep sea cores, and volcanic rocks.

Pleistocene Series

CATEGORY: chronology
DEFINITION: A division of the Quaternary System defined by its deposits. It is a worldwide division of rocks deposited during the Pleistocene Epoch (1,600,000-10,000 years ago). It overlies rocks from the Pliocene Epoch (5.3-1.6 million years ago) and is itself overlain by rocks of the Holocene Series; together these two latter divisions make up the Quaternary System. These deposits contain evidence of humans and their development throughout glacial and interglacial conditions. . By international agreement, the global stratotype section/point for the base of the Pleistocene Series is in the Vrica section in Calabria, Italy. The Pleistocene's boundary with the Pliocene occurs just above the position of the magnetic reversal that marks the Olduvai Normal Polarity Subzone, thus allowing the worldwide correlation of Pleistocene rocks with reference to the magneto-stratigraphic timescale.

proton gradiometer

CATEGORY: tool
DEFINITION: An instrument used in magnetic surveying for detecting the presence of magnetic anomalies; it takes continuous measurements of relative vertical change in intensity of field strength. There are two detector bottles filled with water or alcohol placed at either end of a staff two meters long and held vertically during operation. Protons which form the nuclei of hydrogen atoms in the liquid gyrate or precess; the frequency of precession is identical in the two bottles if no anomaly is present. Any disturbance in the magnetic intensity caused, for example, by a buried feature, results in a different frequency in the two bottles.

proton magnetometer

SYNONYM: proton precession magnetometer
CATEGORY: tool
DEFINITION: An instrument used in magnetic surveying for detecting changes in magnetic field intensity; it takes intermittent measurements of absolute field strength. The detector consists of a bottle of alcohol or water around which is wound an electrical coil of 1,000 turns. The protons, which form the nuclei of hydrogen atoms in the liquid, spin and gyrate in their attempt to align themselves in the direction of the earth's magnetic field intensity. A current of one amp is passed through the coil for three seconds, which aligns the majority of the protons in the direction of the magnetic field thus produced. When this current is cut off, the protons attempt to realign in the direction of the earth's magnetic field; the speed of gyration, or frequency of precession, is amplified and measured in the instrument. This measurement reflects any alteration in the magnetic intensity caused by the presence of fired structures, soil disturbances (e.g. pits, ditches, etc.), or iron objects. It is a highly sensitive magnetometer, used in subsurface detection to record variations in the earth's magnetic field caused by buried iron, kilns, hearths, pits, or ditches.

pulsed induction meter

SYNONYM: pulse radar
CATEGORY: tool
DEFINITION: An instrument used in electromagnetic surveying, mainly for the detection of metals, though on a limited scale it can be used to locate archaeological features. The instrument has a transmitter coil, which sends pulses of magnetic field to the ground: the continuous rising and falling of the field produces eddy currents in metal objects, and magnetic fields in susceptible soil. These are detected by a receiver coil. Only shallow features can be satisfactorily located, and it can be used to find metals, graves, and pottery.

radar interferometry

CATEGORY: technique
DEFINITION: A process used to search for archaeological remains by receiving and analyzing electromagnetic radiation.

resistivity surveying

SYNONYM: resistivity survey
CATEGORY: technique
DEFINITION: A geosurvey survey technique that measures the electrical resistance of the ground for the location of buried features and structures. Any electrical exploration method in which current is introduced in the ground by two contact electrodes and potential differences are measured between two or more other electrodes. It relies on the principle that different deposits offer different resistance to the passage of an electric current depending largely on the amount of water present. A damp pit or ditch fill will offer less resistance, stone wall foundations more, than the surrounding soil. It is one of the most commonly used and least expensive geophysical surveying methods. Readings are taken in a grid-pattern of points all over a suspected site. Variation of resistance through a site is caused mainly by differences in the amount of water contained in pore spaces of deposits and structures. The outline of features may be seen if the readings are plotted as a plan. Although the technique is generally known as 'resistivity surveying', most archaeological surveys use only the ground resistance (in ohms). It compares well with magnetic surveying, as the instruments are simple and cheap and also because modern features such as power cables, iron scrap, and standing buildings do not affect the readings.

scanning electron microscopy

SYNONYM: SEM
CATEGORY: technique
DEFINITION: A technique used to gain information on the microscopic and submicroscopic structure of a wide range of materials ceramics, metals, stone, teeth, hair etc. It involves a type of electron microscope (SEM) in which a beam of electrons systematically sweeps over the specimen, the electron beam passing through a series of magnetic lenses which demagnify the beam diameter. The backscattered electrons and secondary electrons emitted are detected by means of a scintillation or semiconductor counter. The angle at which the beam hits the surface of the specimen determines the number of backscattered and secondary electrons detected, and thus the pattern of contrast represents the topography and elements of the specimen. The signal from these emissions is processed and an image of the object is displayed on a screen. Its advantages over transmission electron microscopy include a greater depth of focus at high magnification and its ability to deal with specimens of much greater bulk, making it less destructive. The chemical composition of the material of the surface can also be deduced from the backscattered electrons. No elaborate specimen-preparation techniques are required for examination in the scanning electron microscope, and large and bulky specimens may be accommodated.

sideways-looking airborne radar

SYNONYM: SLAR, side-looking airborne radar
CATEGORY: technique
DEFINITION: A remote sensing technique involving the recording in radar images of the return of pulses of electromagnetic radiation sent out from aircraft.

sideways-looking airborne radar

SYNONYM: SLAR, sideways-looking airborne radar
CATEGORY: technique
DEFINITION: A technique involving recording in radar images the return of pulses of electromagnetic radiation sent out from a flying aircraft.

SLAR

SYNONYM: sideways-looking airborne radar
CATEGORY: technique
DEFINITION: A remote sensing technique involving the recording in radar images of the return of pulses of electromagnetic radiation sent out from aircraft.

soil conductivity meter

CATEGORY: tool
DEFINITION: A geophysical instrument used in electromagnetic surveying for the detection of metal, but also for the location of archaeological features such as shallow pits, which have a different conductivity from the surrounding soil. The instrument has a transmitter coil which is fed with a continuous sinusoidal current, and a receiver coil; they are mounted at right angles to each other at opposite ends of a horizontal bar about a meter long. The instrument is designed to pick up differences in conductivity between features and the surrounding soil, i.e. the reverse of a resistivity meter. Resistivity surveying is considered more sensitive and versatile.

stacked profile

CATEGORY: geography
DEFINITION: A mapping method which presents the data as a series of layered profiles. Each traverse with the equipment is plotted as a curved profile, then each is placed in order, parallel to each other but aligned on an oblique plan so that a type of 3-D image of the sites's magnetic variatins is obtained. This method can be carried out with a proton precession magnetometer.

thermoremnant magnetism

CATEGORY: technique
DEFINITION: A magnetic moment induced into an item by heat.

transmission electron microscopy

CATEGORY: technique
DEFINITION: A technique used to examine the internal and surface structure and microstructure of materials such as metals, ceramics, and stone. A type of electron microscope is used in which the specimen transmits an electron beam focused on it, image contrasts are formed by the scattering of electrons out of the beam, and various magnetic lenses perform functions analogous to those of ordinary lenses in a light microscope. The sample must be very thin for examination of its internal structure; this is achieved either by grinding and depositing the material on to carbon film, or by preparing thin foils of metallic or non-metallic material by electropolishing or ion-thinning techniques. It is possible to study in detail such things as the wear marks on stone tools or the techniques of potterymaking through examination of the surface.