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Artefact replication by stereolithography
The hlternational Journal of Nautical Archaeology (1998) 27.2:160-165 Article No. na980166
Technical Communication Artefact replication by stereolithography
J. Barto Arnold III Institute of Nautical Archaeology, Texas A & M UniversiO~, P.O. Drawer HG, College Station, Texas 77841-5137, USA
Marc L. M. McAllister hmova International, 850 S. Greenville Ave., Suite 114, Richardson, Texas 75081,
USA
Introduction Artefacts and other physical remains from archaeological sites sometimes must be replicated or copied. The necessity for replicating may arise from the rare and often unique character of the object. The purposes for replicas might include museum exhibit, study collections, extreme fragility, or repatriation of the original. Archaeologists occasionally produce working replicas for purposes of experimentation and study of construction details and techniques. Often in shipwreck collections the original object survived in partial form or was completely missing, existing only as a mould in the encrusting corrosion products. The purpose of this paper is to discuss a new technology useful for creating highly accurate replicas. The technique involved the combination of stereolithography and computed tomography (CT), or threedimensional (3-D) X-ray images. The authors produced replicas of two artefacts from the Padre Islandflota wrecks of 1554. Due to the near complete destruction of the objects which survived as moulds in their entrusting shell and the complicated shapes, replicating these artefacts by traditional casting techniques was not possible. Stereolithography represents a 1057-2414/98102016"0+ 06 $30.00/0
breakthrough for archaeology. This new process made it possible to work with interesting artefacts which could not previously be copied. Both objects were unique in the 1554 collections. Stereolithography also offered a degree of accuracy and detail not obtainable by other methods.
Traditional casting Lysek (1998) presented an excellent description of artefact replication by traditional moulding and casting techniques as practised by Pete Bostrom, a master at copying prehistoric lithic tools. From shipwrecks, the Padre Island flota wrecks of 1554 provided interesting examples of replicating artefacts. Arnold et al. (1995) constructed replicas of the crossbows from one of the 1554 wrecks, the Espiritu Santo (41WY3), to study construction details, for performance experiments, and for museum exhibits. The goat's foot cocking mechanism of one of these weapons was recreated from the natural mould left in the encrustation after the iron had completely corroded away (Olds, 1976: 96-98; Hamilton, 1976: 72-85; 1998). Objects of extreme rarity such as hominid fossil remains were often replicated for study by the many students and © 1998 The Nautical Archaeology Society
J. BARTO ARNOLD I I I & M. L. M. McALLISTER: REPLICATION BY STEREOLITHOGRAPHY
scholars who could not visit the institution housing the original. McAllister recently used stereolithography to copy the many tiny bones of a fist-size dinosaur without removing the rock matrix from the fossils. The replicas were created for the Dallas Museum of Natural History's Dino-World Exhibit (Fiorillo and McAllister, in prep.). The new technique of stereolithography Since 1991, stereolithography, literally three-dimensional printing, has revolutionized the commercial manufacturing and aerospace industries. The process was used for product development and optimization of form, fit and function (Jacobs, 1992; 1996). Manufactured objects from clocks to aircraft consist of many individual parts that must fit together precisely. "The industrial techniques of stereolithography for producing component parts have almost become a sine qua non of product design (McAloon, 1997; Bylinski, 1998). The same techniques recently found their way into medical, dental, archaeological, palaeontological, and physical anthropological applications. Important uses in the arenas of archaeology and physical anthropology were replication of artefacts and anatomical remains. Prior to the advent of stereolithography, researchers used models created from silicon and plaster or epoxy moulding techniques. This process was limited. At best the process was time consuming, and generated a mould that was relatively coarse due to the geometry of the object and the material used to produce the replica. Stereolithography, especially in conjunction with the new high-speed CT scanners to provide a 3-D X-ray image of the original object, constituted a tool that offered a consistently superior product to that of the older process. Companies such as Innova International in Richardson (DalJas) Texas, now routinely construct anatomical and artefact replicas with a slice resolution down to 0-05 mm (0.002 in.). Typically,
however, resolutions of 0-1 mm (0.004 in.) are more than adequate for generating accurate replicas. The process Stereolithography is a process for transferring 3-D designs from a conventional CAD/CAM or medical CT or magnetic resonance imaging (MRI) system to produce accurate prototype models for product development and casting. The fundamental replication production process was based on the fact that a liquid polymer could be changed instantaneously into a solid state when exposed to ultraviolet (UV) radiation, much as silver changes state in normal photographic film when exposed to visible light. The main components of a stereolithography apparatus (SLA) consist of a vat containing a liquid photopolymer, galvanometer controlled mirrors, a directed solid state, or HeCd, UV laser to the surface of the liquid, and just below the surface, a horizontal tray with vertical elevator movements. After the laser had described the shape of a cross-section of the part, the elevator lowered to submerge the newly solid top surface. More liquid resin was deposited onto the surface, covering it, ready for the next layer. The next layer or 'slice' was then described from the computer software, and again the mirrors direct the laser onto the surface of the resin. This process repeated itself, until the object was built. After the object was 'grown' the elevator raised automatically to drain the excess resin. The object was then removed for curing and clean-up. Materials and methods To generate accurate models, the following were required (1) A C T scan, MRI scan, or laser scan of the object to be replicated. The authors obtained CT and MRI scans courtesy of a local hospital. The CT scan provided superior images in the present 161
NAUTICAL ARCHAEOLOGY, 27.2
case. (2) A stereolithography system or other rapid prototyping mechanism capable of generating high resolution models (replicas). (3) Photopolymeric resin, an expensive item. (4) Pre-processing software for converting CT data to the .STL data used by the stereolithography system. (5) Trained personnel conversant with CT and also with pre-processing software. It was wise also to involve the archaeologist in the process to resolve ambiguities and provide guidance to the system operator who was not intimately fafniliar with the artefacts to be replicated.
The build cycle The CT data were translated to an optical disk or DAT tape, then forwarded to the prototyping facility. The information was transferred to a high-power computer and pre-processed into imagery similar to that viewed at the CT station. This imagery was a three-dimensional mathematical description of the scanned object, and could be rotated in any viewing plane. Once the pertinent data of the structure had been determined it was extracted from the full data set and processed into an .STL file. The .STL file was used to drive the laser in the stereolithography apparatus. The SLA machine was primed with resin and the data was downloaded to the machine. Once the SLA machine had copied the model, the replica produced was removed from the chamber for post-processing. This step consisted of removal of a structure generated by the pre-processing software to support the replica during its build up. A final bath in UV light fully cured the photopolymeric epoxy resin. Because of the high-resolution and accuracy of the model, it was usually unnecessary to do any cleaning of the actual replication surfaces. Once the model had been verified as a faithful replication of the CT data, it was available to the archaeologist for study, display, or any other purpose. 162
Rationale The foremost advantage of stereolithography-generated replicas was in the accuracy of the SLA process. Being an additive process, it was not confined to the same limits as traditional moulding techniques. Stereolithographic replica generation produced details of internal structures as well as external. SLA also directly produced the actual object; in other words there was no mould (negative) that was used to create a positive replica. Another advantage of SLA copying was the turnaround time from CT to physical replica. An SLA replica can be generated in a few days from the receipt of the CT scan. Actual SLA machine time was about two hours for the spoon and the same for the sword hilt, both discussed below, if produced separately. By combining them in a single-build cycle, however, both artefacts could be replicated in less than three hours. The two objects used in this study were produced courtesy of Innova International. In a normal commercial setting, the cost might run $250.00 to $550.00. This modest cost is well worthwhile considering the important character of the artefacts.
Summary Industry has widely accepted stereolithography as one of the most accurate, efficient, and cost-effective means of model creation and rapid prototyping. The accuracy obtainable through stereolithography has shown the technology to be a reliable means for high-quality replica generation. The technique, especially in conjunction with modern laser and computer technology, offers a new and consistently more accurate tool for replicating objects Suitable for display and study.
Stereolithography examples from shipwrecks This article is principally concerned with artefact replicas, but the human remains from La Salle's ship, La Belle (41MG86),
J. BARTO ARNOLD Ill & M. L. M. McALLISTER: REPLICATION BY STEREOLITHOGRAPHY
,_,-,,-r,
,,,,.
"
'
Figure 1. Spoon, 1554. Original encrusted object above and replica below. Scale bar is 3 cm. (Photo: J. Barto Arnold)
provided a very recent example of the use of stereolithography in nautical archaeology (Hamilton, 1997). A copy of the skull found was made for two reasons. First, the remains may someday be reburied thus making future study and re-analysis difficult. Second, an accurate copy was sent to a forensic scientist for reconstruction of the facial features of the deceased crewman. This process involved putting layers of clay onto the skull, better done on an accurate copy than on the delicate, three-century-old bones themselves. Stereolithography provided a technique for studying shipwreck artefacts that previously had been left unprocessed because the constituent metal was completely corroded away. In the past, radiographs provided some little information about such encrusted objects, but the metal may originally have been very thin, while the shape of the objects was complex. Both factors prevented casting of replicas. The two artefacts in question, a spoon (Fig. 1) and a sword hilt (Fig. 2) from the Padre Island flota of 1554 (Arnold & Weddle, 1978), were stable and were left intact in their encrusted state. The artefacts were described as follows: ... a large spoon (no. 494), the right size (or a serving piece or tablespoon . . . The metal, probably pewter or silver, is completely corroded but the shape of the bowl can be seen easily in the X-ray (Olds, 1976: 142-143).
. . . a sword or dagger hilt encrusted by corrosion p r o d u c t s . . . (TAC Specimen No. 561)... the object was in three pieces consisting of the pommel and the main body of the hilt, which had split in two along the grip . . . (The stub of) the blade, quillons, knuckle bow, and tang had all corroded, leaving only an impression in the encrustation. The wooden part of the grip, fitted around the tang, was also well preserved, protected by corrosion products from the micro-organisms which usually destroy organic remains in the warm waters of the Gulf of Mexico (Arnold & Godwin, 1990: 221-222).
The replicas of the spoon and hilt produced by the new stereolithography techn i q u e had several uses such as standard morphological description and analysis. Neither object was fully understandable from the standard X-rays produced earlier. They were also useful for exhibition. One can envision an exciting display including the encrusted original, a standard X-ray, an animated CT scan and 3-D depiction, and the physical replica produced from this data.
Conclusions
The advantages of stereolithographic replication of artefacts were clearly manifest. The accuracy was to a very high order, and interior structures were reproduced. There was no danger of damage to delicate objects, and the process was repeatable. 163
NAUTICAL ARCHAEOLOGY,
27.2
Figure 2. Fragmentary hilt of a swept hilt rapier, 1554. Original encrusted object above and replica below. (Photo: J. Barto Arnold)
Time and cost factors compared favourably with traditional casting techniques. Best of all, with stereolithography objects were replicated that in the past could not be copied. Stereolithography is an exciting and valuable new tool for archaeology. Once again, newly developed technology helped elucidated the past.
Acknowledgements David F. Crook, Ph.D. President, of Innova International, Richardson, Texas,
made possible the final production of the artefact replicas on Innova's SLA 3500 machine. John Murray of 3D Systems, Irving, Texas, assisted with early replicas of the spoon produced on his company's SLA-3500 machine. CT scans of the hilt and the spoon were produced by Rocky Velasquez, Imaging Services Coordinator, St. Joseph Regional Health Center, Bryan, Texas. Rick Stryker and Susan de France of the Corpus Christi Museum of Science and History facilitated artefact shipping.
References Arnold, J. B. III& Weddle, R. S., 1978, The Nautical Archaeology of Padre Island: The Spanish Shipwrecks of 1554. Academic Press, New York. Arnold, J. B. III& Godwin, M. F., 1990, A hilt from the 1554 flora. IJNA, 19.3: 221-224. Arnold, J. B. III, Watson, D. R. & Keith, D. H., 1995, The Padre Island crossbows. Historical Archaeology, 29(2): 4-19. Bylinski, G., 1998, Industry's amazing instant prototypes. Fortune, Jan. 1998, 137.1: 120[B]-120[D]. Fiorillo, A. R. & McAllister, M. L. M., in preparation, The Use of Stereolithography in Paleontology. Hamilton, D. L., 1976, Conservation of Metal Objects fi'om Underwater Sites: A Study in Methods. Texas Antiquities Committee and Texas Memorial Museum, Austin, Texas. Hamilton, D. L., 1997, Conservation of the skeleton from the Belle. Conservation Research Report #4, World Wide Web, URL, http://nautarch, tamu. edu/crl/skeletal.ho77, Nautical Archaeology Program, Texas A&M University and La Salle Shipwreck Project, Texas Historical Commission, Austin, Texas. Hamilton, D, L., 1998, Methods of conserving underwater archaeological material culture: casting and molding in conservation, Anth 605. World Wide Web, URL, http://nantarch.tamu.edu/class/ 164
J. BARTO ARNOLD II1 & M. L. M. McALLISTER: REPLICATION BY STEREOLITHOGRAPHY anth605/filel6.htm. Conservation of Cultural Resources I, Nautical Archaeology Program, Texas A&M University. Jacobs, P., 1992, RP&M." Fundamentals of Stereolithography, Society of Manufacturing Engineers Press. Jacobs, P., 1996, Stereolithography and Other Rapid Prototyph~g & Manufacturing Technologies, Society of Manufacturing Engineers Press. Lysek, C. A., 1998, The art of preserving ancient skills. Mammoth Trumpet, 13.2: 12-16. McAloon, K. T., 1997, Rapid Prototyping: A Unique Approach to Diagnosis and Planning of Medica/ Procedures. Society of Manufacturing Engineers Press. Olds, D. L., 1976, Texas Legacy from the Gulf. Texas Memorial Museum and Texas Antiquities Committee, Austin, Texas.
165
Technical Communication Artefact replication by stereolithography
J. Barto Arnold III Institute of Nautical Archaeology, Texas A & M UniversiO~, P.O. Drawer HG, College Station, Texas 77841-5137, USA
Marc L. M. McAllister hmova International, 850 S. Greenville Ave., Suite 114, Richardson, Texas 75081,
USA
Introduction Artefacts and other physical remains from archaeological sites sometimes must be replicated or copied. The necessity for replicating may arise from the rare and often unique character of the object. The purposes for replicas might include museum exhibit, study collections, extreme fragility, or repatriation of the original. Archaeologists occasionally produce working replicas for purposes of experimentation and study of construction details and techniques. Often in shipwreck collections the original object survived in partial form or was completely missing, existing only as a mould in the encrusting corrosion products. The purpose of this paper is to discuss a new technology useful for creating highly accurate replicas. The technique involved the combination of stereolithography and computed tomography (CT), or threedimensional (3-D) X-ray images. The authors produced replicas of two artefacts from the Padre Islandflota wrecks of 1554. Due to the near complete destruction of the objects which survived as moulds in their entrusting shell and the complicated shapes, replicating these artefacts by traditional casting techniques was not possible. Stereolithography represents a 1057-2414/98102016"0+ 06 $30.00/0
breakthrough for archaeology. This new process made it possible to work with interesting artefacts which could not previously be copied. Both objects were unique in the 1554 collections. Stereolithography also offered a degree of accuracy and detail not obtainable by other methods.
Traditional casting Lysek (1998) presented an excellent description of artefact replication by traditional moulding and casting techniques as practised by Pete Bostrom, a master at copying prehistoric lithic tools. From shipwrecks, the Padre Island flota wrecks of 1554 provided interesting examples of replicating artefacts. Arnold et al. (1995) constructed replicas of the crossbows from one of the 1554 wrecks, the Espiritu Santo (41WY3), to study construction details, for performance experiments, and for museum exhibits. The goat's foot cocking mechanism of one of these weapons was recreated from the natural mould left in the encrustation after the iron had completely corroded away (Olds, 1976: 96-98; Hamilton, 1976: 72-85; 1998). Objects of extreme rarity such as hominid fossil remains were often replicated for study by the many students and © 1998 The Nautical Archaeology Society
J. BARTO ARNOLD I I I & M. L. M. McALLISTER: REPLICATION BY STEREOLITHOGRAPHY
scholars who could not visit the institution housing the original. McAllister recently used stereolithography to copy the many tiny bones of a fist-size dinosaur without removing the rock matrix from the fossils. The replicas were created for the Dallas Museum of Natural History's Dino-World Exhibit (Fiorillo and McAllister, in prep.). The new technique of stereolithography Since 1991, stereolithography, literally three-dimensional printing, has revolutionized the commercial manufacturing and aerospace industries. The process was used for product development and optimization of form, fit and function (Jacobs, 1992; 1996). Manufactured objects from clocks to aircraft consist of many individual parts that must fit together precisely. "The industrial techniques of stereolithography for producing component parts have almost become a sine qua non of product design (McAloon, 1997; Bylinski, 1998). The same techniques recently found their way into medical, dental, archaeological, palaeontological, and physical anthropological applications. Important uses in the arenas of archaeology and physical anthropology were replication of artefacts and anatomical remains. Prior to the advent of stereolithography, researchers used models created from silicon and plaster or epoxy moulding techniques. This process was limited. At best the process was time consuming, and generated a mould that was relatively coarse due to the geometry of the object and the material used to produce the replica. Stereolithography, especially in conjunction with the new high-speed CT scanners to provide a 3-D X-ray image of the original object, constituted a tool that offered a consistently superior product to that of the older process. Companies such as Innova International in Richardson (DalJas) Texas, now routinely construct anatomical and artefact replicas with a slice resolution down to 0-05 mm (0.002 in.). Typically,
however, resolutions of 0-1 mm (0.004 in.) are more than adequate for generating accurate replicas. The process Stereolithography is a process for transferring 3-D designs from a conventional CAD/CAM or medical CT or magnetic resonance imaging (MRI) system to produce accurate prototype models for product development and casting. The fundamental replication production process was based on the fact that a liquid polymer could be changed instantaneously into a solid state when exposed to ultraviolet (UV) radiation, much as silver changes state in normal photographic film when exposed to visible light. The main components of a stereolithography apparatus (SLA) consist of a vat containing a liquid photopolymer, galvanometer controlled mirrors, a directed solid state, or HeCd, UV laser to the surface of the liquid, and just below the surface, a horizontal tray with vertical elevator movements. After the laser had described the shape of a cross-section of the part, the elevator lowered to submerge the newly solid top surface. More liquid resin was deposited onto the surface, covering it, ready for the next layer. The next layer or 'slice' was then described from the computer software, and again the mirrors direct the laser onto the surface of the resin. This process repeated itself, until the object was built. After the object was 'grown' the elevator raised automatically to drain the excess resin. The object was then removed for curing and clean-up. Materials and methods To generate accurate models, the following were required (1) A C T scan, MRI scan, or laser scan of the object to be replicated. The authors obtained CT and MRI scans courtesy of a local hospital. The CT scan provided superior images in the present 161
NAUTICAL ARCHAEOLOGY, 27.2
case. (2) A stereolithography system or other rapid prototyping mechanism capable of generating high resolution models (replicas). (3) Photopolymeric resin, an expensive item. (4) Pre-processing software for converting CT data to the .STL data used by the stereolithography system. (5) Trained personnel conversant with CT and also with pre-processing software. It was wise also to involve the archaeologist in the process to resolve ambiguities and provide guidance to the system operator who was not intimately fafniliar with the artefacts to be replicated.
The build cycle The CT data were translated to an optical disk or DAT tape, then forwarded to the prototyping facility. The information was transferred to a high-power computer and pre-processed into imagery similar to that viewed at the CT station. This imagery was a three-dimensional mathematical description of the scanned object, and could be rotated in any viewing plane. Once the pertinent data of the structure had been determined it was extracted from the full data set and processed into an .STL file. The .STL file was used to drive the laser in the stereolithography apparatus. The SLA machine was primed with resin and the data was downloaded to the machine. Once the SLA machine had copied the model, the replica produced was removed from the chamber for post-processing. This step consisted of removal of a structure generated by the pre-processing software to support the replica during its build up. A final bath in UV light fully cured the photopolymeric epoxy resin. Because of the high-resolution and accuracy of the model, it was usually unnecessary to do any cleaning of the actual replication surfaces. Once the model had been verified as a faithful replication of the CT data, it was available to the archaeologist for study, display, or any other purpose. 162
Rationale The foremost advantage of stereolithography-generated replicas was in the accuracy of the SLA process. Being an additive process, it was not confined to the same limits as traditional moulding techniques. Stereolithographic replica generation produced details of internal structures as well as external. SLA also directly produced the actual object; in other words there was no mould (negative) that was used to create a positive replica. Another advantage of SLA copying was the turnaround time from CT to physical replica. An SLA replica can be generated in a few days from the receipt of the CT scan. Actual SLA machine time was about two hours for the spoon and the same for the sword hilt, both discussed below, if produced separately. By combining them in a single-build cycle, however, both artefacts could be replicated in less than three hours. The two objects used in this study were produced courtesy of Innova International. In a normal commercial setting, the cost might run $250.00 to $550.00. This modest cost is well worthwhile considering the important character of the artefacts.
Summary Industry has widely accepted stereolithography as one of the most accurate, efficient, and cost-effective means of model creation and rapid prototyping. The accuracy obtainable through stereolithography has shown the technology to be a reliable means for high-quality replica generation. The technique, especially in conjunction with modern laser and computer technology, offers a new and consistently more accurate tool for replicating objects Suitable for display and study.
Stereolithography examples from shipwrecks This article is principally concerned with artefact replicas, but the human remains from La Salle's ship, La Belle (41MG86),
J. BARTO ARNOLD Ill & M. L. M. McALLISTER: REPLICATION BY STEREOLITHOGRAPHY
,_,-,,-r,
,,,,.
"
'
Figure 1. Spoon, 1554. Original encrusted object above and replica below. Scale bar is 3 cm. (Photo: J. Barto Arnold)
provided a very recent example of the use of stereolithography in nautical archaeology (Hamilton, 1997). A copy of the skull found was made for two reasons. First, the remains may someday be reburied thus making future study and re-analysis difficult. Second, an accurate copy was sent to a forensic scientist for reconstruction of the facial features of the deceased crewman. This process involved putting layers of clay onto the skull, better done on an accurate copy than on the delicate, three-century-old bones themselves. Stereolithography provided a technique for studying shipwreck artefacts that previously had been left unprocessed because the constituent metal was completely corroded away. In the past, radiographs provided some little information about such encrusted objects, but the metal may originally have been very thin, while the shape of the objects was complex. Both factors prevented casting of replicas. The two artefacts in question, a spoon (Fig. 1) and a sword hilt (Fig. 2) from the Padre Island flota of 1554 (Arnold & Weddle, 1978), were stable and were left intact in their encrusted state. The artefacts were described as follows: ... a large spoon (no. 494), the right size (or a serving piece or tablespoon . . . The metal, probably pewter or silver, is completely corroded but the shape of the bowl can be seen easily in the X-ray (Olds, 1976: 142-143).
. . . a sword or dagger hilt encrusted by corrosion p r o d u c t s . . . (TAC Specimen No. 561)... the object was in three pieces consisting of the pommel and the main body of the hilt, which had split in two along the grip . . . (The stub of) the blade, quillons, knuckle bow, and tang had all corroded, leaving only an impression in the encrustation. The wooden part of the grip, fitted around the tang, was also well preserved, protected by corrosion products from the micro-organisms which usually destroy organic remains in the warm waters of the Gulf of Mexico (Arnold & Godwin, 1990: 221-222).
The replicas of the spoon and hilt produced by the new stereolithography techn i q u e had several uses such as standard morphological description and analysis. Neither object was fully understandable from the standard X-rays produced earlier. They were also useful for exhibition. One can envision an exciting display including the encrusted original, a standard X-ray, an animated CT scan and 3-D depiction, and the physical replica produced from this data.
Conclusions
The advantages of stereolithographic replication of artefacts were clearly manifest. The accuracy was to a very high order, and interior structures were reproduced. There was no danger of damage to delicate objects, and the process was repeatable. 163
NAUTICAL ARCHAEOLOGY,
27.2
Figure 2. Fragmentary hilt of a swept hilt rapier, 1554. Original encrusted object above and replica below. (Photo: J. Barto Arnold)
Time and cost factors compared favourably with traditional casting techniques. Best of all, with stereolithography objects were replicated that in the past could not be copied. Stereolithography is an exciting and valuable new tool for archaeology. Once again, newly developed technology helped elucidated the past.
Acknowledgements David F. Crook, Ph.D. President, of Innova International, Richardson, Texas,
made possible the final production of the artefact replicas on Innova's SLA 3500 machine. John Murray of 3D Systems, Irving, Texas, assisted with early replicas of the spoon produced on his company's SLA-3500 machine. CT scans of the hilt and the spoon were produced by Rocky Velasquez, Imaging Services Coordinator, St. Joseph Regional Health Center, Bryan, Texas. Rick Stryker and Susan de France of the Corpus Christi Museum of Science and History facilitated artefact shipping.
References Arnold, J. B. III& Weddle, R. S., 1978, The Nautical Archaeology of Padre Island: The Spanish Shipwrecks of 1554. Academic Press, New York. Arnold, J. B. III& Godwin, M. F., 1990, A hilt from the 1554 flora. IJNA, 19.3: 221-224. Arnold, J. B. III, Watson, D. R. & Keith, D. H., 1995, The Padre Island crossbows. Historical Archaeology, 29(2): 4-19. Bylinski, G., 1998, Industry's amazing instant prototypes. Fortune, Jan. 1998, 137.1: 120[B]-120[D]. Fiorillo, A. R. & McAllister, M. L. M., in preparation, The Use of Stereolithography in Paleontology. Hamilton, D. L., 1976, Conservation of Metal Objects fi'om Underwater Sites: A Study in Methods. Texas Antiquities Committee and Texas Memorial Museum, Austin, Texas. Hamilton, D. L., 1997, Conservation of the skeleton from the Belle. Conservation Research Report #4, World Wide Web, URL, http://nautarch, tamu. edu/crl/skeletal.ho77, Nautical Archaeology Program, Texas A&M University and La Salle Shipwreck Project, Texas Historical Commission, Austin, Texas. Hamilton, D, L., 1998, Methods of conserving underwater archaeological material culture: casting and molding in conservation, Anth 605. World Wide Web, URL, http://nantarch.tamu.edu/class/ 164
J. BARTO ARNOLD II1 & M. L. M. McALLISTER: REPLICATION BY STEREOLITHOGRAPHY anth605/filel6.htm. Conservation of Cultural Resources I, Nautical Archaeology Program, Texas A&M University. Jacobs, P., 1992, RP&M." Fundamentals of Stereolithography, Society of Manufacturing Engineers Press. Jacobs, P., 1996, Stereolithography and Other Rapid Prototyph~g & Manufacturing Technologies, Society of Manufacturing Engineers Press. Lysek, C. A., 1998, The art of preserving ancient skills. Mammoth Trumpet, 13.2: 12-16. McAloon, K. T., 1997, Rapid Prototyping: A Unique Approach to Diagnosis and Planning of Medica/ Procedures. Society of Manufacturing Engineers Press. Olds, D. L., 1976, Texas Legacy from the Gulf. Texas Memorial Museum and Texas Antiquities Committee, Austin, Texas.
165