Archae Solenhofen (firstname.lastname@example.org)
Last modified December 10, 2002
Copper coring drills
Large diameter copper tubes (as well as being made of other materials, including brass, tin plate, and soft steel) called coring barrels are used today by amateur lapidists for the coring of rocks and minerals (Sinkankas 1984). These coring barrels are generally thin-walled to reduce as much as possible the volume of rock that needs to be cut away. A coring bit is made by attaching the coring barrel to a wooden dowel, and the coring barrel can often exhibit a groove or gap along the length of the tube to allow new abrasive to more easily reach the cutting surface during use. Today, coring drills can be powered by an electric motor, but they can also be powered by hand, such as with a bow.
In Egypt, a number of carpentry bowdrills have been found that were used by the ancient Egyptians (Fig. 1, Petrie 1974a). The bow was much wider at one end to allow for a handhold, and the drill-stock was made of wood, and sometimes contained a discharge hole to help eject the drill bit (Petrie 1974a, image). The capstone bearing was of wood or hard stone, and had a hole in one end for the insertion of the drill-stock. An example of a modern experiment in fire making using a replica of a small ancient Egyptian bowdrill is presented in the following website.
Fig. 1. Ancient Egyptian bowdrill (after Wilkinson 1878).
Many representations in Egyptian art of bowdrill usage is known (Singer et. al. 1954, Aldred 1978, Scarfe 1975, Stocks 1989). The first known depiction of the bowdrill is in the 5th dynasty tomb of Ty at Saqqara, however, the tool must have existed earlier since a number of bored wooden objects exist from the Early Dynastic Period (Nicholson & Shaw 2000). Examples of other depictions include a carpentry drill used for boring wood (Fig. 2a), and a lapidary drill employed in the manufacturing of stone beads (Fig. 2b, See Bead Making). Hand-powered stone borers were also used by the ancient Egyptians for the hollowing of stone vases (Petrie 1974a, 1977, Stocks 1993), and representations are found in Egyptian art (Fig. 3a-b).
No tubular copper barrels or the wooden drill-shaft used for coring of rock have been found in the archeological record from ancient Egypt, or from Mesopotamia and Crete where rock coring was also employed (Stocks 1993, Warren 1969). For the copper barrel, this may be due to the wearing down of the copper tube to lengths that were no longer usable, at which point the remaining copper tube was recycled (Stocks 1993). The use of bow- and hand-powered coring drills as a method of cutting rock is inferred from marks observed on ancient Egyptian stoneworks, finished and unfinished stone objects, and pieces of waste rock. The cores (Fig. 5, UC44986, UC68247, UC44988, UC43723, UC43893, UC44987, UC44989, UC44991, UC55364) and core holes (Fig. 19, UC44990, UC16039,UC16038, UC33315, UC33317) are generally tapered (Petrie 1883), however, in the manufacturing of vases the walls of the core and core hole appear to be parallel throughout the cut (Fig. 6, Petrie 1974a, Stocks 1993; See Stone Vase Making). Both cores and core holes are often observed to be striated (e.g. an unfinished granodiorite porphyry bowl image). These striations are observed to be of the concentric and also spiraling variety (Fig. 5, Petrie 1883, Stocks 1999; 2001, Chris Dunn's website). The diameter of the cores and core holes vary from about 0.6 cm up to possibly 70 cm, and are dependant on the type of rock cut. Travertine (Egyptian alabaster) and limestone shows the smallest diameter cores, and igneous rocks are generally above about 5 cm in diameter (Petrie 1883). The largest diameter core holes are found in limestone and siliceous sandstone, with the largest being on the order of 45 and 70 cm (Petrie 1883; 1974a). The 45 cm coring bits appears to be used to dress down a platform of limestone, and the 70 cm bit could possibly have been used to cut a slab of rock, since the core could not be detached from the bottom of the core hole otherwise. The maximum length of the cores are restricted by friction forces generated by the rotation of the coring barrel, and clogging due to the build up of compacted tailings between the coring barrel and the walls of the core and core hole (Stocks 1999).
Fig. 2. a) Egyptian carpenters using a bowdrill. b) Beadmakers using a triple bit bowdrill and threading beads for a necklace. Both from a tomb at Thebes c.1450 BC (after Singer et. al. 1954).
Fig. 3. a) Tomb representation of vase making using a boring tool. b) Tool reconstruction of type used in gypsum vessel manufacturing (after Hodges 1964).
Fig. 5. Granite core (UC16036) from Giza of 4th Dynasty date. (height. 11 cm. The Petrie Museum, Photograph by Jon Bodsworth The Egypt Archive) Note: Higher Res. image.
Ancient Egyptian coring barrels would have been made of copper, either cast or cold-worked until the Middle Kingdom, when bronze tools became more readily available. Some ancient core holes still contain weathered copper or bronze residue and rock tailings/abrasive (Lucas and Harris 1962, Stocks 1986). The ancient Egyptians began to make tools of smelted copper by cold-working and casting starting around 3500 BC (Hoffman 1980). The technique of cold-working copper into sheets by hammering existed in early dynastic Egypt, where thin-walled copper vessels have been found (Petrie 1977). The ability of the ancient Egyptians to make copper and bronze tubes, either with sheeting or by casting, is demonstrated in examples of cylindrical vessels (Petrie 1974b) and pipes for plumbing (Wilkinson 2001). The thicknesses of the coring barrels are inferred from tubular slots left on the bottom of stone objects (Fig. 6), and were on the order of 1 to 5 mm (Arnold 1991). Casting of copper tubes with 5 mm thick walls can be accomplished with molds of sand (Stocks 1999).
Fig. 4. Unfinished travertine stone vessel split longitudinally to reveal remaining drill core fragments partially attached, possibly 4th Dynasty (height. 6.9 cm, The Petrie Museum (UC44993), Photograph by Jon Bodsworth The Egypt Archive)
Copper and bronze are insufficient in terms of indentation hardness to cut by abrasion the majority of minerals in hardrocks such as basalt, diorite, granite, metagreywacke (slate/schist), and siliceous sandstone (quartzite). A harder material than the metal itself is required as an abrasive in order to cut these rocks. This abrasive material could have been used as shards of rocks or crystals used as cutting teeth, charged copper or bronze (abrasive impregnated into the metal), or as loose abrasive grains. It is unlikely that cutting teeth were used, since they would quickly loose their sharp edges, essential for efficient lapidary cutting of rock. It is unlikely that the ancient Egyptians had a ready source of mineral abrasives with hardnesses greater than that of quartz (Lucas and Harris 1962). The most likely abrasive is loose quartz sand, with its ease in replacing worn abrasive grains, as the main material used for cutting rocks for most of the ancient Egyptian's history. An example of a 4th Dynasty basalt fragment can be found at The Petrie Museum, in which the saw cut still contains rock tailings and sand (UC16033).
Fig. 6. Metasiltstone ornamental bowl with coring slot from the Step Pyramid, 3rd Dynasty. (d. 38 cm., Cairo Museum, Photograph by Jon Bodsworth The Egypt Archive)
For examples of rock coring in ancient Egypt (see: Petrie, 1883; 1974b, Lucas & Harris 1962, Arnold 1991, Stocks 1999; 2001): a) Spy-holes in the a limestone wall of the serdab of Djoser at the north base of the Step Pyramid at Saqquara (3rd Dynasty, Fig. 7).
b) Core marks and peg holes on the sarcophagus in the King's chamber of the Great Pyramid (4th Dynasty, Stock 1999, Fig. 8, image 1, image 2).
Fig. 7. Spy-hole from the serdab of Djoser near the Step Pyramid at Saqquara (Photograph by Jon Bodsworth The Egypt Archive)
c) Core hole between the feet of the anorthositic gneiss statue of Khafre (4th Dynasty, Lucas & Harris 1962, Fig. 9).
Fig. 8. Coring mark on the granite porphyry sarcophagus of the Great Pyramid, 4th Dynasty. (Photograph by Jon Bodsworth The Egypt Archive)
d) Sockets in granite from the Valley and Sphinx Temple of Khafre used for the ends of door-posts (4th Dynasty, image 1, image 2, image 3, Fig. 10).
Fig. 9. Core hole on the diorite gneiss statue of Khafre, 4th Dynasty. (Cairo Museum, Photograph by Jon Bodsworth The Egypt Archive)
e) The travertine alter at the Sun Temple of Niuserre, near the pyramids of Abusir (5th Dynasty, image 1, image 2). f) Marks of a coring drill are found on a block from the complex of Neuserre (5th Dynasty, Borchardt 1907), with traces of verdigris from the copper coring barrel (Reisner 1931)). g) Bolt sockets for a locking mechanism in a granite door lintel near the pyramid of Pepi II (6th Dynasty, Fig. 11)
Fig. 10. Granite door post socket in the Sphinx Temple, 4th Dynasty. (Photograph by Jon Bodsworth The Egypt Archive)
h) Marks on a granite sarcophagus with partial coring holes in a lid-peg socket (21st dynasty, image). i) Petrie gives many additional examples of core holes and cores (Petrie 1883). Drawing #7 Granite drill core found at Giza (Fig. 5.). Drawing #8 Part of a cast of a pivot hole lintel from a granite temple at Giza. In this example the core is not entirely removed, and remains to a length of 20 mm. Drawing #9 Travertine mortar (UC16038) found at Kom Ahmar, broken in course of manufacture, showing the core in place. Drawing #10 A small travertine core found with others at Memphis. Drawing #11 A marble eye for inlaying, with two core holes made with thin coring bits, one within the other. Drawing #12 Part of the side of a core hole in diorite (UC16039) exhibiting regular spaced grooves from Giza. Drawing #13 A limestone fragment (UC16041) from Giza, showing how closely holes were placed together to remove material by coring. j) Petrie (1974a) presents a number of examples. An unfinished travertine vase, exhibiting a core and core hole with parallel sided walls, in which part of the core is still attached (Fig. 12, UC33311).
Fig. 11. Bolt sockets in a granite door lintel near the pyramid of Pepi II, 6th Dynasty. (core hole d. 10 cm, Photograph by Jon Bodsworth The Egypt Archive)
A tube cut from basalt (Fig. 13), which could be done by centering and cutting two core holes of different diameter and then detaching the tube. This is a method still used today by amateur lapidists for the making of cylindrical vessels and bracelets (Long 1976, Fig. 14). Another example of tube making by the ancient Egyptians is an Early Dynastic period metasiltstone ornamental bowl, the tube is left attached and the surrounding rock is removed (Fig. 15, image 1).
Fig. 12. Cross-section of an ancient Egyptian unfinished travertine vessel with parallel core and core hole walls (after Petrie 1974a).
Fig. 13. Drill core waste fragment made of basalt (UC44985), double cored to producing a tube, unknown date possibily 4th Dynasty. (height: 8.3cm, The Petrie Museum, Photograph by Jon Bodsworth The Egypt Archive) Note: Higher Res. image.
Petrie (1977) also states that many stone vessels contain a tubular slot on the inside base, the remnants of the coring hole used in the initial stages of hollowing, similar to modern stone vessel manufacturing (Can narrow-necked stone vessels be made today?) i) An example of a partially completed porphyry vessel on display in the Cairo Museum (JE18758), demonstrating how the coring drill was used to remove waste rocks in the manufacturing of stone vessels (Stocks 1999, image 1, image 2, image 3, image 4, image 5). Eight core holes can be observed with 7 closely spaced around the perimeter of the inner surface, and one in the center, for which the tubular coring slot is still visible. This method of removing waste rock reduces the effort necessary for the manufacturing of stone vessels, and is a common time-saving technique still used today.
Fig. 14. Modern coring of cylindrical shaped stone vessels (after Long 1976). Fig. 15. Rock tube in center of the metasiltstone ornamental bowl from the 1st Dynasty tomb of Prince Sabu (Tomb 3111 (Emery 1949-58)). (tube d. 10 cm, Cairo Museum, Photograph by Jon Bodsworth The Egypt Archive)
Stone borers and drills were also used by the ancient Egyptians. Lucas and Harris (1962) gives examples of drilling with copper or stone points, where the drill holes are still clearly visible. For example: a) Marks on two pieces of inscribed stone vases of diorite and dolomitic limestone, from the Step Pyramid at Saqqara (3rd Dynasty) b) Marks on a diorite bowl of Khaba (3rd Dynasty) c) The nostrils, ears and corners of the mouth of an alabaster statue of Menkaure (4th Dynasty). Many stone beads have been found with holes drilled for threading. Figure 16 presents a number of unfinished beads that contain holes from the Temple of Memeptah. Small flint drill-bits and borers, used in the manufacturing of beads, can be found at The Petrie Museum (UC14877).
A limestone block with 10 boring sockets with circular striations and ridges (somewhat similar in appearance to those in a center cup of a 3rd Dynasty travertine ornamental dish from Saqqara: image) from the mastaba of Perneb at Saqqara (Arnold 1991). The holes are randomly distributed over the top of the block's surface with some slightly overlapping at the edges. Objects such as these may represent an underlying block used to bore completely through a number of rock object that rested on top of it (Arnold 1991), or possibly a waste piece of rock used to practice bowl or other stone vessel boring skills. The making of circular ridges during boring can be associated with changing of the borer's size during hollowing. An example of these ridges can be observed in a sectioned alabaster vessel (Fig. 17). Another example of multiple bore holes is a fragment of limestone with four bore holes found in waste rock near the pyramid at Meydum (Petrie 1974b). It is described by Petrie as a possible pivot for wooden levers used to move large blocks of stone. Petrie (1974b, Fig. 18) also describes a small fragment of limestone that has a number of randomly spaced partially completed core holes (Fig. 19).
Fig. 16. Unfinished calcite beads from the Temple of Memeptah, Third Intermediate Period. (The Ashmolean Museum, Photograph by Jon Bodsworth The Egypt Archive)
Stocks (2001) constructed a partial rotary-motion coring drill powered by a wooden bow (Fig. 20). The coring barrel was made of copper and was 8 cm in diameter, 1 mm in thickness, and was partially forced fitted to the wooden drill-shaft. A capstone bearing was carved out of a hard sandstone with flint chisels and punches, so that the rounded cone end of the drill-shaft could rotate with reduced friction when aided by grease, as well it acted as a weight. The wooden bow was made from a curved tree branch that applied enough tension to the bow rope to prevent slippage of the wooden drill-shaft during the coring experiment.
Fig. 17. A cross-sectioned Middle Kingdom travertine vessel from the Southern Pyramid at Mazghuneh. (The Manchester Museum, Photograph by Jon Bodsworth The Egypt Archive) Fig. 18. Fragment of possible limestone pivot block (UC30857) used with levers of unknown date. (height: 5.2 cm, The Petrie Museum, Photograph by Jon Bodsworth The Egypt Archive) Fig. 19. Limestone fragment (UC44990) on which coring drills have been used of unknown date. (height: 4.5 cm, The Petrie Museum, Photograph by Jon Bodsworth The Egypt Archive)
A granite block from Aswan was used to test the coring drill. Initially, the surface of the granite was flattened by pounding with a diabase (dolerite) hammer. An outline equal to the diameter of the cutting edge of the coring bit was marked on the surface of the rock with red paint, and this outline was used to guide the carving of a shallow groove into the surface of the granite with a flint chisel and stone hammer. This was done to prevent the coring bit from slipping from the area being cut, during the initial stage of coring. This slippage was no longer a problem when the depth of the cut exceeded 5 mm. Stocks (1993, p.601) describes a travertine vessel with a similar type groove on the top surface located in the collections of The Petrie Museum (Fig. 21).
Fig. 20. Representation of the coring drill used in the rock cutting experiments of Stocks (1993, 2001).
The drilling was conducted by a team of three workman using dry sand as an abrasive. Two workmen operated the bow at either end, and the third held the capstone. As the bow was drawn back and forth, the motion produced 120 revolutions of the coring bit per minute (60 clockwise and 60 anticlockwise). A force of about 1 kg/cm2 on the end of the coring bit was needed to initiate cutting of the granite by abrasion by quartz sand. This was easily obtained by the workman holding the capstone, however, some difficulty was noted in keeping the drill stable and perpendicular to the granite surface during the reciprocating motion of the bow. This caused the granite rock core and the core hole to became tapered, as well as the core hole being overcut in the direction of the bow's motion. However, this effect was reduced as the core depth increased, and the overcutting of the core hole was kept symmetrical by changing the orientation of the bow during drilling.
Fig. 21. Unfinished travertine stone vessel marked with red paint for coring with drill, possibly 6th Dynasty (height. 7 cm. The Petrie Museum, Photograph by Jon Bodsworth The Egypt Archive)
The dry sand abrasive (quartz) was added at the top of the core hole and some of it worked its way down to the cutting surface as the coring proceeded. Wet sand appeared to make the drilling more difficult than that of dry sand. When dry sand was used the tailings of the drilling process were removed by hand after extraction of the drill, and were found to be compacted on the sides of the copper tube. The rock core was removed from the core hole by hammering two chisels into the tapered groove, and the core was extracted in a single piece after breaking off near the bottom of the core hole. Stocks (2001) notes the presence of concentric horizontal striations. As in the case of the slabbing saw experiment, this may be the result of angular quartz fragments embedded in the copper coring barrel, or possibly the compacted tailings on the walls of the coring barrel. The striations were up to 2.5 mm in width and deeply cut, and are similar in appearance to those observed on some ancient Egyptian artifacts (Stocks 1999; 2001).
The experiment took 20 hours to complete and generated a rock core 6 cm in length. A rate for cutting granite with dry quartz sand abrasive of 5.2 cubic cm/hour was obtained. The ratios of volume, weight, and depth of removal between the copper barrel and the granite block are presented in Figure 22. Because of the inexperience of the work teams in these modern experiments, it was suggested by Stocks (2001) that the rate of cutting could be increased by a factor of 2 with gained experience.
Fig. 22. Ratios of granite/copper lost during the coring drill experiment (after Stocks 2001).
Stocks also conducted experiments on cutting limestone with bow-powered coring drills. The rate of cutting limestone with a copper barrel was 15 times greater than that observed in granite (Stocks 1999). The rate of copper loss would be expected to be very low, due to the similarity in hardness between the mineral calcite and copper. This was demonstrated by coring drill experiments conducted by Stocks (1993), in which a ratio of length of copper barrel lost from the drill bit to stone depth penetrated was less than 1:100. Copper tube coring drills would be very effective in the working of most limestones, since quartz abrasive is about 5 times the indentation hardness of calcite. Travertine, a limestone with a high rock hardness, would be more difficult to cut than a porous limestone due to its dense nature.
Gorelick and Gwinnett (1983) conducted coring experiments using a bow-powered drill with a copper barrel. In these experiments they used dry and wet quartz sand abrasive, as well as fixed points, and both dry abrasive and slurries of emery, corundum, and diamond. Test of the different method of abrasion were successfully demonstrated in the coring of granite. Their tests, however, did not exhibit concentric striations in both the wet and dry experiments using quartz sand as was observed in Stocks (2001). This may be the result of differences in the quality of the quartz abrasives used in the experiments. Both, diamond and corundum produced concentric striations, but emery was only found to produced them when used as a water or olive oil slurry. It is unlikely that the ancient Egyptians had ready sources of emery, corundum, or diamond in the quantities necessary for an effective abrasive for most of their history, if at all (Lucas and Harris 1962, Arnold 1991)
These experiments demonstrate that the ancient Egyptians could have, using simple technology and the material available to them during their history, worked rocks with copper or bronze coring drills powered by hand or bow. It would be expected that for soft stones like limestone it was routinely used. In the case of hardrocks like granite, the expense incurred by the loss of copper during the cutting process would restricted it to royal monuments and stone objects, for usage where other tools would not suffice (Arnold 1991). The only large-scale usage of the coring drill was the manufacturing of sarcophagi (Arnold 1991) and stone vessels. Stocks (1989; 1997) proposes that the tailings of the cutting process could be used in the manufacturing of faience, from a water-based paste of calcite derived tailings (from limestone and travertine coring) and sodium bicarbonate (natron). As well, blue glazes can be produced from diorite and granite tailings. Both the blue glazes and the faience produced by Stocks resemble both in appearance and chemically those common to the ancient Egyptian's. Stocks (1993) suggests that granite tailings could also be used as a polishing abrasive because of its 0.5-5 micron grain size, and also as a abrasive for the drilling of beads. A grain size of 5 microns (0.0002") is ideal for lapping gloss finishes on rock surfaces, since the transition from frosted to semigloss lapidary finishes occurs with abrasives about 15 micron in diameter, and high quality lapidary polishes are generally done today with abrasive grain size of 6 (0.00025") to 0.5 microns (0.00002") (Craig & Vaughan 1981).
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