Waterjetting 15a - Carving a Stonehenge

This post is a marriage of two different themes that have recently appeared at Bit Tooth. The first, under the Waterjetting title, has contained a discussion of the different aspects of high-pressure waterjet use. The second, more recent theme discussed both the original Stonehenge and then how the MS&T Stonehenge, which is a working calendar, functions. In this post I am going to talk about how the MS&T megalith was built, and since it involves the use of high-pressure water it seems appropriate to include it in the Waterjetting Series.

As I have noted in one of the earliest waterjetting posts we had learned, from Russian literature, back in 1966 that waterjets could be used to cut into granite. From results of an unplanned test, we had learned that the pressures needed to cut through granite need not be that high. Others had predicted that it would take a jet pressure of up to 30-times the rock compressive strength in order to penetrate rock efficiently. However both the Russians and ourselves had been able to drill through a 30,000 psi granite with a waterjet pressure of only around 10,000 psi, rather than the predicted 900,000 psi.

We had done this by moving the jet over the surface so that, as the jet passed across the cracks between grains, so it would penetrate and pressurize the crack, causing it to grow and remove the grain, without having enough pressure to cut through the grain itself.

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

We had drilled this block of rock back in Leeds and the nozzle was pointing vertically downwards, as we rotated the rock beneath it. After drilling a shallow central hole, we stepped the nozzle out a short distance and repeated the process, breaking the outer ring of rock to the central core. Then after widening the hole, we could come back to the center and advance the nozzle into the rock, and repeat the process. Because of the nozzle size we had to continually step the hole to a smaller diameter as the hole got deeper, and thus there is a rapid taper to the walls.

Moving forward to the early 1980’s when Chancellor Marchello asked Dr. Marian Mazurkiewicz and I to cut the rock for his Stonehenge, and we knew that we could cut the rock at a pressure below 15,000 psi (the size of the pump that we had at the time). But tests where we had made multiple passes over a rock had shown that, with a direct vertical cut to an edge, that repeated passes would taper the cut inward over time – naturally doing what we had done artificially at Leeds.

Figure 2. Early tests on granite cutting. Note that the lower cut was made with two jets diverging at about 5 degrees, and the one above it with the jets diverging at 11 degrees. (The nozzle was spinning and moved across the face of the rock several times).


These tests showed that we needed a higher angle to ensure that the sides did not taper, and while this could be achieved with the nozzles angled at 15 degrees to the perpendicular, because the jets had to cut a path wide enough for the nozzle to enter the slot, an angle of 45 degrees was used after a short series of experiments.

Our team at the Rock Mechanics and Explosives Research Center (RMERC) had been asked to carve the rock, since we had just prior to the commission, been down in Georgia demonstrating to the granite industry there that waterjets were able to economically cut granite.

Figure 3. Starting to cut a 1-inch wide slot in granite, pressure 14,000 psi, 90 rpm, linear cutting speed around 9 ft/min, areal cutting rate around 20 sq. ft./hour.( Raether, R.J., Robison, R.G., Summers, D.A., "Use of High Pressure Water Jets for Cutting Granite," 2nd US Water Jet Conference, Rolla, MO., April, 1983, pp. 203 - 209.)

Concurrently with showing that this could be economic we had also shown that the technique removed the respirable dust from the air that is generated with a flame-torch cut, and that the noise level would drop to industrially acceptable levels from the “jet engine roar” of a cutting torch.

Figure 4 Showing the flame at the bottom of the burner spalling its way through the granite.

Figure 5. Cutting granite with a flame-jet lance, Graniteville MO 1979. (Note the cloud of very fine particles of granite being blown out of the right side of the slot).

The first thing to do in arranging to cut several hundred tons of granite was to find a source of supply. Unfortunately, at that time the granite quarries in the South-East part of Missouri were closed and other sites in the state did not prove practical. But because we had done the work with the Elberton Granite Association in Georgia, we were able to arrange to purchase rock from one of the Quarries around Elberton, Ga. They themselves had recently constructed their own version of the standing stones, the Georgia Guidestones although these had been cut to shape using flame jets, rather than water.

Figure 6. The Georgia Guidestones, Elberton GA.

The granite blocks were roughly split to shape in the quarry, and then shipped to Rolla by train. The first block was sent by truck and this proved the benefits of rail, although the size of the cars limited the scale of the monument to half that of the original in the UK. Which meant that the blocks – over 11 ft tall – were one-eighth the weight of the originals.

Figure 7. Blocks of granite in the cutting frame. The cutting lance is the thin rod in the center of the picture.

The blocks were brought to the RMERC and placed in position using a crane. Dr. Mazurkiewicz and his students had built this frame from wooden blocks, with the guide rails made from radio antenna mast. The lance moved on a cross-beam, also made from radio antenna mast. The low reaction force from the jets meant that the forces on the structure were very small. Thus the head itself could be pulled along the track using a bicycle chain, and small, fractional horse-power motors could be used to move the head and advance it into the slot. Although, by that time, self-rotating heads had been developed, it was decided that a better control of the cut edges could be achieved if the head was hydraulically rotated.

Figure 8. Detail of the cutting platform. The two hoses feed a hydraulic motor that gear-drives the rotation of the cutting lance. The high-pressure water feeds through the hose to a small swivel at the top of the lance. A small electric-motor driven screw behind the platform elevates and lowers it on the guide rails to advance the nozzle into the cut.

In order to keep the slot width as narrow as possible the nozzle holder was made as small as the feed pipe, with the two jets issuing from small carbide inserts within the holder.

Figure 9. Detail showing the nozzle holder and a nozzle orifice on the lance.

Experiments showed that an effective cutting rate of around 20-square feet an hour (depending on the direction of cut relative to the planes of the granite) could be achieved. The lance was rotated at 90 rpm, and moved down the cut at a speed of 9-ft per minute. The two jets, at a pressure of around 14,000 psi (there was some pressure loss in the system) would cut into the rock around 1/3rd of an inch on each pass, and the lance would be lowered this amount after the pass, and then the direction reversed and the jets would cut back along the rock. (This is somewhat faster than the hand-held stone flattening of the original Stonehenge rocks in England, although studies in Peru, where a similar technique was used to shape to blocks that build Machu Picchu showed that it is possible to flatten about 1 square foot an hour once you learn how to chip the rock). Professor Parker Pearson has also noted that the UK original had the rocks finally shaped after they had been erected).

Figure 10. Showing the jet arrangement, raised after a side had been trimmed so that the jets could be seen. Normally with the jet in the cut there is little to show the cutting action.

It took about a morning to cut one side of a block (or in later stages to cut one of the large blocks in half for the smaller stones). Once the second side had been cut, the block was turned and the rail aligned to cut the third and fourth sides. Overall, given that the operations had to be shut down during the winter where the temperatures were below freezing, the blocks were cut and completed over the course of two semesters, largely working with undergraduate student labor.

After the blocks were cut, they were taken to the site, where each was placed in position using a crane. Because of the precision required to align the blocks with the sun, this was a time-consuming operation. The major standing stones were then held in place with an additional pour of 18-inches of cement. (They stood on a cement platform).

Figure 11. Lowering a block into place.

The monument was dedicated at the Mid-summer solstice in 1984, with John Bevan, a Druid of the Gorsedd performed the dedication.

Figure 12. Speakers at the Dedication: Dr. Joe Senne – who designed the megalith; John Bevan – Druid; Dr. John Carlson – from the Center for Archaeoastronomy; Dr. Joseph Marcello – Chancellor.

The construction was sufficiently novel that it was awarded one of the ten Engineering Awards from the Society of Professional Engineers.

(Note there is a video of the construction available on DVD. This shows, in part, that the jets can trim an edge without any material on one side, something other tools find difficult, because the nozzle does not contact the rock). There are also other articles that I have written answering some questions and describing the site on the RMERC web page.)

A Calendar for the Ages - the MS&T Stonehenge part 2

In the last post I discussed the historical background to the British Megalith Stonehenge, and briefly how it was decided to create a similar construction, albeit at half-scale, on the campus of what is now Missouri University of Science and Technology (MS&T). So we skip forward about 4,000 years from time of the last post and the new Chancellor of our campus wanders into the refreshment room at a Conference on Engineering Education in Oklahoma. There he saw one of his new faculty – and over a glass or two of the water of life (uisge beatha) mentioned that he had interest in a Stonehenge, while I mentioned that we had just developed a new method for cutting granite, and I had some idea of where to get the rock. Before I knew where we were, I was on a committee, and we were planning a monument.

The campus was already in process of building a new Mining Building, itself near the Computer Science building, and there was a nearby space beside the campus Observatory. And this became the site for the new megalith. (It consists of 55 stones). As with the early constructions, this was planned to be a working calendar, and Dr. Senne used computer models to predict the positions of the sun, and the North Star to ensure that the monument would be an accurate model for at least four millennia. But, because it was in a different location, and because of the limited space, we had to modify the Neolithic design. So this post will describe how the megalith acts as a calendar and then the next will describe how we made it. (It had to be half-scale because even at that size a single stone filled a rail car).

Figure 1. An ancient monument recreated (with modern power generation in the background)

The solar alignments were built around the center of the structure, and this can be found as a small metal disk, which has been surveyed into place by the National Geodetic Survey, and mounted in a cylinder of concrete.

Figure 2. The marker at the center, with the dot in the triangle being the focus.

The first and major alignments, as with the original, are those that mark the position of the sun at midsummer, and midwinter. The stones are aligned so that the sun can be seen as follows:

At midsummer the sun will rise over the Heel stone. This 35-ton block of granite at the far end of the approach walkway is not exactly aligned at present, since the church behind it conceals the very first seconds of the sunrise, but it is close. A tree that initially marred the alignment to the center of the stone has since died, and the alignment is now better than it was when built. The alignment should not change over the coming millennia. (Granite erodes at around one inch every thousand years, and the Heel Stone is set in a full truckload of cement, to guard against earthquake-induced movement).

Figure 3. View of the Heel Stone from the central marker (lower front right).

As the sun passes through the sky that day it will move relatively around the southern half, past the East and West markers, and at sunset will lie between the two legs of the North-West trilithon.

Figure 4. View of the North-West Trilithon, the midsummer sunset through these legs casts an orange beam that reaches to the central marker column, at its diameter. (lower front left).

For the midwinter sunrise, the current McNutt Hall, housing the Departments of Mining and Metallurgy, hides the first few minutes of the rising sun, yet the sun still first appears through the legs of the South-East trilithon. As time has passed the antenna on the building that, fortuitously, marked the point where the sun was first seen has been removed.

Figure 5. Looking through the South-East Trilithon to the point where the sun rises at midwinter.

During the course of that day the sun moves over its relatively shorter arc, and at sunset appears to go down between the legs of the South-West trilithon. As with other alignments the construction of the University residences has slightly displaced the true alignment to the sunset on the horizon. For the next few years I suspect that the tree that is now growing into that view will further block this alignment.

Figure 6. Looking through the South-West Trilithon, from the central marker, toward the midwinter sunset.

This gives us two days of the year, which really aren’t enough to define the seasons, but one can add two more, based on the two equinoxes in March and September. On those days the sun rises directly in the East, and sets directly in the West. Thus, by putting small notches on the East and West marker stones, the day the sun rises and sets in those places identifies two additional days.

Figure 7. The notches on the a) East and b) West marker Stones, with a notch on each to mark the sunrise and sunset at the two Equinoxes.

This still, however, only gives us four days, and the Chancellor was decidedly against adding the nineteen stones to give the ancient calendar. Dr. Senne suggested, and it was agreed, that the site should be “Americanized” and that the calendar should be based on the use of the sun position, as developed by the Anasazi Indians in Colorado.

However, instead of their complex curves, he suggested a simple analemma carved into two central stones that would mirror the position of the sun at midday as projected through a small hole set within the Southern Trilithon assembly.

Figure 8. Points showing the position of the sun at midday over the course of the year. (Stanford Solar Center)

The inverse of this curve (since it was projected through a small orifice) was therefore inscribed onto the two stones in the center. The faces carrying the inscription were the only two faces not cut with high-pressure water within the construction.

Figure 9. The central stones carrying the analemma markings.

For the winter half of the year, when the sun is lower in the sky, the sun’s image will fall on the vertical face, during the summer half the sun is higher and the image will fall on the horizontal face. At the equinoxes the sun image travels along the joint between the two stones.

Figure 10. A small brass plate is mounted just below the capstone of the Southern Trilithon. There is a small hole in this plate through which the sun’s image is projected onto the faces of the two central stones. (It takes about ten minutes or so, on either side of midday, for the image to cross to the line and then again to move off the stone.)

The analemma was scribed into the stone with a sand-blaster after Dr. Senne had laid a full-scale tracing on the rock, to show the required positions. To make it easier to identify the actual date the line has been marked at five-day intervals within each month, which are also identified.

Figure 11. The sun’s image centered on the line at midday on the ?th of ?. (You need to read the date from the analemma).

Unfortunately this marker is likely to erode away over the next 500 years, at which point, unless it is renewed, the calendar will cease to function. In his book Mike Parker Pearson noted that the lower surfaces at Stonehenge had been shaped, but it is hard to know, after this passage of time, whether there were superficial markings on the stones, such as we have created, that would give a different way of telling the days of the year.

There was one other thing that we added. Although the North direction is shown with its own marker stone, this might get displaced, or lost. Thus a window was created in the Northern Trilithon, so that a person of normal height, standing between the light wells beside the central marker, will see (on a clear night) the Pole Star within the window, for (Dr. Senne assured us) the next 4,000 years.

Figure 12. The Polaris Window on the Northern Trilithon.

I will complete this series with a short post on how we cut and installed it, next time.

A New view of an old Circle - Post one on Stonehenge

Back in 1983 I was asked to work on the construction of a Stonehenge monument to be built on the campus of what is now Missouri University of Science and Technology. The new Chancellor of the campus, Dr. Joseph Marchello, had helped establish the Center for ArcheoAstronomy at the University of Maryland. He had wanted to build a Stonehenge, and we had just developed a new way of cutting rock with high-pressure water, and had contacts with the Georgia Granite Association as a result. The monument, which ultimately consisted of 55 different stones, was designed by Dr. Joseph Senne, who was then Chair of the Civil Engineering Department on campus. But to understand why we built ours, one has to understand why the original was built, on Salisbury Plain in the UK, some 5,000 years ago. And this discussion has been helped by the new book “Stonehenge – A New Understanding” by Mike Parker Pearson, discussing the recent Stonehenge Riverside Project.

Figure 1. Location of the original Stonehenge (Google Earth)

Although there are legends that it was built by the Druids, they actually came after the circles had been built, and it should be remembered that, when the Romans came to the UK 2,000 years ago Stonehenge was already over 2,500 years old.

Figure 2. Romans versus Druids – the Roman version

In looking back on that period remember that the history was written by the Romans and that they had to justify their invasion. Thus the picture that they paint of British society at the time is colored by those needs, and their image of Druids as backward painted savages is unlikely to be close to reality.

But why was there a need for these circles? Well back some 50,000 years ago mankind had migrated out of Africa and slowly spread through Europe and Asia. But as they spread they originally retained their cultural structure as hunter-gatherers.

Figure 3. The migration of humanity from Africa into Europe and Asia (National Geographic DNA project)

They reached Spain and Portugal as Cro-Magnon man, but were still largely hunting and subsistence gathering at that time. Such groups are small, typically, as one sees with the Hatzabe in Africa today, they number around 20 individuals.

Figure 4. The Hatzabe a family group of about 20 individuals.

The group size is similar with the Sami in Scandinavia, families that still follow the herds of reindeer as they have done for millennia.

Figure 5. A Sami family group of reindeer herders from Northern Scandinavia

Such tribes (including the Bakhtiari of Iran that Bronowski documented in “The Ascent of Man”) are migrant, and do not have time for much other than staying alive. But, with time, the culture changed and people began to farm. This change began around 12,000 years ago, likely in the Middle East. It was not until 6,500 years ago (4,000 BC) that trees began to be cleared and farms established in Southern England.

One of the advantages of farming is that the tribe does not have to move continuously to sustain itself. Cronon, in Changes in the Land, notes that in non-agricultural Maine the population was sustained at around 41 persons per hundred square miles. With the beginning of agriculture further south in New England (pre-European arrival) the native peoples could sustain 287 people in a similar area. More intense development of crops and the domestication of animals followed, leading to larger and more closely knit communities.

But there is one problem with the switch to agriculture on an increasing scale, one needs to know when to plant the crops. And while initially this was likely imitative of nature, over time the tribes needed to develop a calendar.

Lying by the fire and staring up at the stars to work on the idea Neolithic Man was living in what we now call the end of the Stone Age. And they noticed that at different times of the year the moon lay at different points in the sky. And so they started to plot these positions, after a while they noticed that there were grooves on some of the local rocks, left from earlier glaciation, that aligned with the positions of the moon at mid-winter and mid-summer.

Figure 6. Grooves in the rock near Stonehenge (Dr. Parker Pearson ibid)

This led on to marking the positions of the moon (and possibly also some of the stars as was the practice in native tribes in America). These markings were made more permanent as they were more confident of their positioning, through the use of wooden poles. (Note that there is a similar though more primitive wooden circle at Cahokia in Illinois dating at around a thousand years ago).

Figure 7. Circle of wooden poles – the UK Woodhenge (Dr. Parker Pearson)

The village grew into the town of Durrington Walls, with wooden houses, which have been recently excavated to show the yellow-painted clay floors, and the location of beds, dressers and other wooden furniture.

Figure 8. Artist’s rendition of the town of Durrington Walls (Dr. Parker Pearson)

With confidence, and as the calendar became more reliably used, so the wooden poles were replaced with a more permanent set of bluestone columns that had been brought to the site up the river Avon.

Figure 9. An early stone circle – Bluestonehenge- on the banks of the Avon. (Dr. Parker Pearson)

There is a little controversy over what happened next, but it has been suggested that around this time a new set of folk, now known as the Beaker people, because they used clay pots with a spout (beaker) moved into the region. They had one critical difference to the earlier site inhabitants, in that they worshipped the sun, rather than the moon. Thus the old calendar would not work. But up where the grooves cut into the stone, they had set four stones (the Station Stones) into the ground in a rectangle to mark the position of mid-summer and midwinter moonrise. If you rotated around the stones ninety degrees, then these poles still marked the two days, but now they did it for the sun’s positions. This could not have been a co-incidence, and so the study of calendars proceeded, but at the new site, further up the hill at the current Stonehenge.

Figure 10. Alignment of the Station Stones (Dr. Parker Pearson)

And on a passing note, as I once mentioned in Nature, and Rodney Castelden noted in “The Making of Stonehenge” the rocks were likely hauled into place with oxen, which might be why the roads are so wide).

Figure 11. Oxen hauling the stones to the site (Rodney Castleden ibid)

The first major construction at the Stonehenge site was the surrounding ditch and mound of rock (which is a relatively soft chalk that can be excavated with antler picks) with a series of small pits (some of which have been found to contain human remains) set within the ring.

There has been discussion as to whether this was a ceremonial burial ground for high-ranking individuals. In much the same way as Bruce Bourque has noted in “The Swordfish Hunters” discussing the Red Paint People of Maine, the small number of burials, relative to the size of the local population and the length of time this existed, means that this could only be a special place and rite. So though it might be where high class folk were buried (as with Westminster Abbey) it had other uses, which was to develop the calendar.

Over the years a number of different circles, with a variety of pole positions, were tried. For a while the 28 and a half stones of the Sarsen Ring had favor, but the last stone circles they put in had nineteen stones (probably taken from the Bluestone ring at the bottom of the hill). Then they stopped. They had a calendar.

Figure 12. Part of the bluestone ring of smaller stones set within the Sarsen Ring at Stonehenge. The Heel Stone can be seen further back from the main circle. (Landscape Perception)

But why nineteen? Well nineteen times nineteen is 361. Add the four days when, in the Hyperborean calendar, “time stood still”, which have come down as the Celtic feast days Samhain, Imbolc, Beltane and Lughnasadh, and you have a remarkable resemblance to the 365 days of the year. The problem was solved for a couple of thousand years.

Until, of course, those pesky Romans showed up, and made us work with months of 28, and 30 and 31 days. Herumph!!

I’ll talk about the Building of the MS&T Stonehenge next time!.

Waterjetting 8c - dealing with graffiti

When I began this series I mentioned that the target material plays an important part in deciding which pressure and flow rate is best for a particular task. Sometimes time also has a role, and not always in the way of "faster is better". I mention this because we made a mistake once. (Well we only made this mistake once, didn’t mean we haven’t made other mistakes). Almost thirty years ago we carved the granite blocks that make up the Missouri S&T Stonehenge, a half-scale Americanized version of the British megalith. The campus Americanized it when Dr. Joe Senne, the Civil Engineering professor who designed it, incorporated an analemma, based on the calendar developed by the Anesazi in New Mexico. This replaced the 19-stone inner bluestone ring of the original.


Figure 1. The MS&T Stonehenge

The MS&T Stonehenge was chosen as one of the ten Outstanding Engineering Achievements of 1984, by the National Society of Professional Engineers, in part because the 160-ton 53-stone structure was carved from Georgia granite by high-pressure waterjets, without the use of abrasive. It has, over the years, generated a lot of interest (even getting me onto the Tonight Show with Jay Leno) but that has also included the odd local “artist” who has adorned it with graffiti.

My initial response, when this first happened, was to go over to the monument immediately with a high-pressure pump and start to wash the paint off. And that was the mistake, for two reasons. Firstly the paint was not totally dry, and secondly we had not protected the stone with an invisible protective coating to seal it. Thus when we tried to wash the paint away, while we removed all the surface paint, and to a casual observer it remains clean, we had driven a small fraction of the still liquid part of the paint into the pores and grain boundaries of the granite. Thus, if you know where to look, there is still a slight discoloration where that first writing was removed.

Shortly after that, on the advice of the Georgia Granite Association, the campus found a coating that was applied to the rock, sealing the pores and grain boundaries, and future cleaning was made a lot easier and more effective. However it did not completely solve the problem, since future cleaning had to be done in such a way as to remove the spray paint, while leaving the protective coating.

And that reminds me of a funny story. Graffiti is a significant urban problem, and it costs cities like Albuquerque in New Mexico about $1.3 million a year in clean-up costs. Much of incentive for almost immediate removal is because it is a way for street gangs to mark their territory, and this motivates police to urge an aggressive treatment policy.

But what happens if it is art? There are street artists who, in various ways, not related to gang activity, have chosen to decorate, for free, generally abandoned buildings. Perhaps the most famous of these is Banksy, recently making the news when a piece he painted on a London wall appeared in a Miami auction house, where it was anticipated to be worth around $600,000 before being withdrawn from the auction.


Figure 2. Bansky "wall art" estimated to be worth up to $600,000. (Banksy)

At one time Albuquerque had a similar idea, of hiring those who were spraying the town walls to instead create works of art on some of the otherwise blank concrete surfaces such as bridge abutments around town.

Unfortunately this led to an awkward situation. One of the local artists had painted some of his art on a fly-over. Shortly thereafter the city sent a crew out to cover up the remaining graffiti with a coat of whitewash. Unfortunately the crew were not artistically trained, and so covered up the new work of art.

For some years I had a photograph of a waterjetting crew working on that site. At first glance they were removing graffiti, but in reality they were taking the white coating from the painting to re-expose it to public view.

And this is one of the advantages that waterjets possess in that they can, with care and training of the personnel, be used to preferentially remove individual layers of material, whether of dirt or paint, without doing any damage to the material underneath, the substrate of the surface.

This is important, for example, in removing paint from buildings where the underlying substrate may be a relatively weak wood surface, where any high jet pressure would be enough to eat away the softer parts of the wood turning a smooth wooden sill into an etched and rough surface far from the desired result. Thus, in these circumstances, there is a need for very fine pressure control if the desired result is to be obtained.

And sometimes the material that is to be removed is not that easy to remove with water power alone, at an acceptable rate, because the pressure has to be lowered to the point that it only removes the paint at a slow, and uneconomic rate. At that point it is possible to add a relatively soft abrasive, something like a baking soda, that will not only be effective in removing the material, but is soft enough that it will do relatively little damage to the surface. At the same time many of these softer abrasives are also soluble, which means that the costs of clean-up can also be reduced.

In some cases the water pressure need be little more than tap pressure.


Figure 3. Figure 3. low pressure waterjet graffiti removal using soluble abrasive.

The Red Paint People, Doggerland and my DNA.

Over the last couple of months I have been putting up the occasional post on my own family tree, as it is becoming defined by DNA analysis, and at the same time have been looking at some of the early arrivals of Indians in Maine and the North East American continent. (My interest in the latter was initiated by the question of when Europeans first arrived on the continent in enough numbers to influence facial features of the locals).

Two weeks ago I was fortunate to be able to attend a lecture by Bruce Bourque, the Curator of Archaeology at Maine State Museum, and the authority on the Red Paint People, of whom I have written earlier with a follow-up post on their travels. His talk, and the book he just recently released (The Swordfish Hunters) provides much more detail on a people that have largely been neglected by “the archaeologists of Harvard,” who have tended to disregard significant developments this far north of Boston.

The Red Paint People are also called “the Moorehead Phase”, after Warren Moorehead, who first identified them as the “Red Paint” people, because of their custom of burying red ocher with the bodies in their cemeteries. They flourished in a small part of Maine, and their cemeteries have been found along the banks of local rivers. There is, however considerable evidence that they harvested fish and sea-food (their cemeteries have been found in large shell middens), with a peculiarity that they also hunted, ate and used the bones and rostra (the “sword”) of local swordfish. The latter, in particular, was used to provide a stiffened mount behind the harpoon and spear tips used in hunting. They appear to be the first to hunt swordfish, which would have been a dangerous prey for early Holocene man, since they have a nasty habit of attacking the boats of those who have just stabbed them with a harpoon.

Figure 1. Red Paint Cemeteries in North-East America (The Swordfish Hunters)

The book is a fascinating story of detective work, and archaeology as it builds a picture of a people that began around 5,000 years ago and suddenly disappeared around 3,800 years ago. Dr. Bourque points to evidence that it does not fit within an overall unified culture which has been described as the Maritime Archaic, but rather stands on its own, and emerges from the “Small Stemmed Point” tradition that preceded it. But is totally separate from the Ceramic period that follows.

One of the intriguing parts of the story lies in the thousand-mile link with the Ramah Peninsula in Labrador, that I discussed in a previous post, and Dr. Bourque also points to close similarities between the findings in Maine, and those at the Port au Choix site. One identifying characteristic lies in the development of stone gouges, for use in hollowing out the inside of dugout canoes.

Figure 2. A Stone Gouge from Maine, and an artist’s rendition of how it would be hafted. (The Swordfish Hunters).

The gouges, as the book argues, show that the Red Paint Peoples were building substantial canoes and boats around 4,000 years ago, that were substantial enough for voyages of a thousand miles, and that this would also make them viable for use in harpooning swordfish (an art in itself as the book illustrates).

The climate change around the time that this culture was flourishing in Maine is not seriously discussed in the book, but I think that it is worth looking at, in context, because it ties in a little with what was happening across the Atlantic, where the culture that built Stonehenge had moved into Britain.

Figure 3. Climate swings in the Northern Hemisphere over the past 10,000 years (the Holocene) (Consulting Geologist)

The significance of these temperature variations is often significantly discounted as climate scientists today would rather emphasize the point of the effects imposed by man, rather than the natural effects we cannot control. Yet the higher temperatures that did exist, even as recently as the last (Medieval) Warming Period are evidenced, for example, by the recent uncovering of an Eskimo village which has been buried under a glacier for the past 500 years. The inhabiting tribe of Yup’ik Eskimo lived, among other things, on caribou and lived at Quinhagak in Alaska. Without the protective ice cap that has covered the site from the time that the Yup’ik left there at the beginning of the Little Ice Age, the site is now rapidly being eroded into the Bering Sea (a fate that is similarly threatening the sites in Maine, where coastal erosion and sea level changes have covered most of the Red Paint People’s locations). But it indicates that we are only now reaching the temperatures at that site that prevailed in the Medieval Warming Period.

The Red Paint People lived at the beginning of what is now referred to as the Minoan Warming Period. And, from data obtained from the Greenland Ice Cores, it is possible to note a couple of facts about the time that the tribe appears to have vanished. First, if the temperatures, as derived from the Ice cores recovered from Greenland are examined in a little more detail:

Figure 4. Temperatures in the region over the last 5,000 years (from the Greenland GISP2 Ice core)

Perhaps more to the point, if the extent of sea ice at the time is considered (from the same source) it fell to an historic low during the Minoan.

Figure 5. Sea Ice extent over the Holocene (The Ice Chronicles ) (Note the plot has been flipped, relative to the original, in order to conform to the consistency of showing the older period to the left of the plot in the rest of the post).

With this considerable warming the ice retreated from the shores of Greenland, and it became an even more hospitable place that it was at the time almost 3,000 years later when Erik the Red came calling. This warming had another consequence, because it led to a steady rise in the levels of the sea. This is shown in the book as it affects Maine, important since it shows how the shoreline dwellings from the period have since been inundated.

Figure 6. Sea levels off the coast of Maine over the Holocene (The Swordfish Hunters)

But in Europe that sea rise from the beginning of the Holocene had another consequence. It flooded the land-bridge (known as Doggerland) between what became the isle of Britain and the continent.

Within the British Isles, by 4,000 BP the country had been colonized for about a thousand years by the arrival of an agricultural movement that displaced the earlier hunter-gatherers and, in turn. rapidly changed from a “slash and burn” land clearance into the development of a “celtic arrangement of fields. Colin Burgess in "The Age of Stonehenge" has noted that the settlements towards the end of that transition were already being constructed defensively.

A more recent unmarked burial pit at Fengate contained three disarticulated burials and one, crouched, the latter with a leaf-shaped arrowhead still sticking between the eighth and ninth ribs.

The warmer clime was conducive to the spread of agriculture and an increasing density of population. The cutting of the land bridge, and the slow flooding of what later became the Dogger Bank, in the North Sea, had a personal consequence.

Figure 7. The location of Doggerland about 7000 BP (Bryony Coles via doggerland)

My Y-chromosome has been designated as R1b1b2a1a1d*, which is a variety of Celt, that, as I have mentioned in an earlier post, had come down from Cro-Magnon man. The analysis that has evolved over the past few years (apparently starting at 23andme suggests that this a “Freisian” variety of Celt and there is a body of thought moving to the conclusion that they were the inhabitants of Doggerland that were driven to Britain when the final inundation occurred around 5500 years ago, just before the first circles at Stonehenge were constructed. (And here I now discover that maybe I wasn’t the first of my lineage to work on a Stonehenge).

The first circles at Stonehenge were developed about 5,000 years ago (at the left side of Figure 4). But around 2150 BC or some 4000 BP the Beaker People arrived. In contrast with those, maybe us, who had first developed the site and were moon worshipers, they worshiped the sun. What made the Stonehenge site become what it did was that the simple markers already there to align critical lunar phases could, by moving around the circle ninety degrees, also align to the major solar alignments at mid-winter, mid-summer etc. The ruling elites of the time became more powerful, and with the warmer climes helping sustain agricultural production, society became more static. And the more powerful had enough manpower available to develop, over the next millennium or so, the full glory that became Stonehenge. They also grew into the Wessex Culture with its elaborate and rich graves.

The Beaker People were Celts and still, at the beginning of this time, used stone axes and flint-shaped arrowheads. But copper daggers are found even in the earliest graves and this was the time where the culture was moving into the Bronze Age in Britain, some time after it had developed elsewhere in Europe.

Given that the Red Paint People were aware of native copper deposits, (and were starting to make small ornaments with them) had they known of the metal forming traditions developing in Europe then metal objects would have shown up in the graves. They did not, and even to the time of Champlain stone tools were in use.

So it is logical to conclude that seafaring though the cultures were on both sides of the Atlantic they did not communicate at this time, at least not well enough to teach metal craft, at a time when it might have been easier to travel, from one side of the Atlantic to the other. On the other hand, it might be possible to conjecture an explanation for the long and narrow bayonet points which Dr. Bourque points out as a significant feature of Red Paint burials. He notes that these are too weak to have any great utilitarian value in society, because they were made of stone. He therefore suggests that they had only a ceremonial aspect that has been lost. But it could be that they were an attempt to copy the spear heads that were beginning to be developed in Britain at the time, but which were made utilitarian only by being made of metal. And that would suggest some form of communication between the two societies.

There remain a couple of additional thoughts, both about the ability of early societies such as these to travel long distances, and the mysterious disappearance of whole societal segments. But they arise in events in Greenland that happened during the Medieval Warming Period; the migration of the Thule from Alaska to Northern Greenland in 1000 AD, and the abandonment of the Western Settlement of the Viking in Greenland. Since this is a different time period I will therefore leave those topics to a subsequent post.

Waterjetting 2b - crack growth and granite sculpture

The last post in this series showed that the main way in which waterjets penetrate into materials is by growing cracks that already exist within the material, and I used glass as an example to show that this was true.

It is this process during which water penetrates into cracks, and then comes under pressure, either by the impact of more falling water (say under a waterfall in nature) or because the water freezes and then thaws, that causes the cracks in the rock to grow under natural attack, and the rock to slowly erode. As this happens the cracks slowly grow and extend to the point that they meet one another, separating small pieces of rock from the solid.

Within the body of a piece of rock the largest cracks that exist are normally at the boundaries of the grains of different minerals that make up the bulk of the rock. (Back in 1961 Bill Brace showed that the strength of a rock reduced as the square root of the increase in the grain size of that rock ).( Brace, W. F. (1961): Dependence of fracture strength of rocks on grain size. Bulletin of the Mineral Industries Experiment Station, Mining Engineering Series. Rock Mech. 76, 99± 103.) More recently, though still back in 1970, my second grad student, John Corwine, showed that it was possible to predict the strength of a block of granite, knowing the size of its crystals.

Which makes a good time to tell a little anecdote. Back when I was doing my own doctorate at the University of Leeds (UK) we were looking at how waterjets drilled through rock, and how that might be used to make a drill. We had already run some tests of different rocks that we placed under a nozzle, and gradually raised the pressure of the jet to see what pressure it took to make a hole in the rock. Tests on granite had shown that the jet (with a maximum pressure of just under 10,000 psi) would not drill a hole into those rock samples, and so the granite had been set aside. But, with the equipment just finished and yet having to go to lunch, I asked Dennis Flaxington, the lab technician helping me, to put a new sample into the rig so that we could run a test in the afternoon. When I came back I found that he had used a piece of granite. I made several disparaging remarks, at which point he noted that, having spent some significant time putting the rock in the apparatus, I should just go ahead and run the test (which normally took about 5 minutes) rather than being an unmentionable. And so we did, and as I posted earlier, this is the resulting hole in the rock, which we were now able to drill right through in a process that took about half-an-hour.

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

How could this now work, when a single jet clearly did not penetrate into the granite in the earlier tests? The answer is that as we moved the rock under the nozzle (we were slowly spinning the rock under the nozzle, and then raising the rock, since at the time there were no high-pressure swivels available for us to use) the jet passed successively over the edges of the different crystals in the granite. As it entered and pressurized these small fractures, the pressure in the crack was enough to grow the crack and remove individual crystals along the jet path. By starting at the center, and taking successive passes around the axis a large depression was cut into the surface, and the rock could then be raised, and a second smaller layer removed. Repeating this slowly removed the rock in front of the nozzle, and at the end of the test we had drilled through 9 inches of granite.

From this experience, over time we went on to cut, for a University, a lot of granite. Obviously, to cut at a competitive rate we had to cut at a higher pressure that just 10,000 psi. But, after showing that we could cut Georgia granite at a competitive rate in tests run at 15,000 psi down in Elberton, Georgia, Dr. Marian Mazurkiewicz and I led a group of our students in cutting 53 blacks of that granite to form the MS&T Stonehenge that now sits on the University campus.

Figure 2. View of the Stonehenge at Missouri University of Science and Technology, the vertical blocks are some 11 ft tall. The entire sculpture was cut by high pressure water jets operating at between 12,500 and 15,000 psi. (MS&T RMERC ).

Cutting commercially is not quite as simple as it might appear, since larger blocks such as those shown in Figure 2 will contain rock that varies quite significantly in properties as the cuts progress. In the Stonehenge case the rock came from close to the top of the quarry, and the cracks in the rock were quite well defined. Some fifteen years later we were fortunate enough to be asked to cut a second sculpture, but this time working with the internationally acclaimed artist, Edwina Sandys. Edwina had designed a sculpture for the campus, the Millennium Arch, which required that we cut two figures from blocks of Missouri granite, and polish them to create one group, while using the original pieces as part of an Arch that would stand some 50 ft away.

Figure 3. The Millennium Arch at Missouri University of Science and Technology. (Each vertical leg of the Arch is some 15 ft long, and the figures removed and in the background, are 11 ft tall). Better images can be found here.

The vertical legs were first cut to shape, and then the figures cut out from them. In order to contain the crack growth to limit the amount of material removed the cutting lance had two jets inclined outwards and the lance was rotated at around 90 rpm, as the lance made repeated passes over the surface, removing between a quarter and half-an-inch of rock on each pass, until it had penetrated through the rock. It took 22 hours of cutting to isolate the female figure from the host block. The slot width was around an inch, and there was some significant difficulty in cutting this slot as the quality of the rock changed within the blocks being cut. (The problem was solved by raising the cutting pressure).

Figure 4. Partial cut for one of the figures of the Millennium Arch, checking the depth.

This second sculpture illustrates both an advantage and a problem for the use of waterjets in cutting rock pieces. Use of the water gives a relatively natural look to the rock, although the vertical surfaces of the arch and the capstone were all actually “textured” to look natural using a hand-held lance at 15,000 psi. (The rock is a little harder than that from Georgia and most of the cutting took place at around 18,000 to 20,000 psi). But when the polished surfaces for the inside of the verticals and the isolated figures were prepared the rough initial surface required much more time to grind and polish flat, than a smoother initial cut would have needed.

Because water alone penetrates along crystal and grain boundaries in the rock the surface left is relatively rough. This gets to be even more of a problem if waterjets are used to cut wood. Here the “grain” boundaries are the fibers in the wood structure. Thus when a relatively low pressure jet (10,000 pai) cuts into the wood, it penetrates between the fibers and the cut quality is very poor. One of the first things I have asked students to do, when given the use of a high pressure lance for the first time, was to write their name on a piece of plywood. Here is an example:

Figure 5. Student name written with a high-pressure jet into plywood. Note that areas of the wood around the jet path are lifted by water getting into the ply beneath the surface layer, and that part of the top ply between cuts is removed in places.

I thought about having you guess the student name, Steve, but this is one of the more legible ones. (Female students generally cut the letters one at a time and were more legible, male students tried to write the whole name at once).

There are many similar examples that I could use to illustrate that, while there are tasks where waterjets alone work well, when it comes to precision cutting, then adding a form of sand to the jet stream to provide a much more limited range to the cutting zone can give a considerable advantage, and so the field of abrasive waterjet cutting was born, and discussion of that topic will lead, in time, to a whole series of posts.