Vinland Map Authentication: A Case Study for the Review of

Article Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

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Vinland Map Authentication: A Case Study for the Review of Spectroscopic Techniques and Application of X‑ray Methods Elizabeth C. Landis* Department of Chemistry, College of the Holy Cross, Worcester, Massachusetts 01610, United States

J. Chem. Educ. Downloaded from pubs.acs.org by ST FRANCIS XAVIER UNIV on 08/29/18. For personal use only.

S Supporting Information *

ABSTRACT: Authentication of the Vinland map manuscript, supposedly from the 15th century, was used as a case study in an undergraduate upper-level instrumental-analysis class. The case provides a review of spectroscopic techniques and data analysis from several nondestructive techniques. Assessment of the case shows it to be particularly beneficial for student understanding of X-ray techniques. KEYWORDS: Upper-Division Undergraduate, Analytical Chemistry, Inquiry-Based/Discovery Learning, Spectroscopy

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INTRODUCTION The use of case studies in chemistry teaching can be an effective way to transfer knowledge while also encouraging active student participation and analysis of real-life situations.1−3 Case studies have been widely used in biology, with repositories of possible materials available to instructors. A 2011 survey of case-study-using teachers found that 90% were in biology- or biomedical-related areas.4 The use of case studies in chemistry has been relatively rare. There are a limited number of published case studies at the intermediate or advanced level. This lack of published case studies in chemistry is seen as a major impediment to casestudy implementation.5 For example, the National Center for Case Study Teaching in Science Case Collection contains only 20 cases in the broad category of “Chemistry, Undergraduate upper division.”6 The Analytical Sciences Digital Library (ASDL) includes five case-study topics.7 The case studies published in these collections also demonstrate the broad diversity within case studies and the need for varied resources, as published cases range from brief in-class activities and demonstrations to laboratory-based projects.8−10 Instrumental analysis courses often cover a wide range of instrumentation including numerous spectroscopic techniques. At the end of the spectroscopy unit, students have typically learned about molecular-spectroscopic techniques, including UV−visible spectroscopy, fluorimetry, Fourier-transform infrared spectroscopy, and Raman spectroscopy, as well as the atomic techniques of atomic absorption spectroscopy and atomic emission spectroscopy. Students may have also been introduced to the X-ray techniques of X-ray diffraction spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Students can struggle with deciding which technique is appropriate for a problem, particularly when students have a higher level of comfort with the techniques used during introductory chemistry classes, such as UV−vis and infrared spectroscopy. In this paper, I report the use of the authentication of the Vinland map manuscript as a case study for an advancedundergraduate-level instrumental-analysis course. A unique aspect of the case is the combination of spectroscopic© XXXX American Chemical Society and Division of Chemical Education, Inc.

technique review and applications. Quantitative assessment showed that the case study was perceived by students to be particularly helpful in understanding the theory and applications of X-ray-based spectroscopic techniques. Learning Objectives

The aim of this case was to increase student interest in instrumental chemistry. I was introduced to the case method in an educational workshop and sought to apply the technique in my instrumental-chemistry class. On the basis of the workshop results, case-study use had the potential to improve student interest in instrumental chemistry through use of real-world problems while also improving student understanding of specific content. For this case, the content-learning objectives focused on improving student confidence and understanding in selecting spectroscopic techniques for a given application. Following the case, students should be able to compare and contrast techniques, propose analysis plans, and defend their choices. The application of X-ray diffraction spectroscopy, Xray photoelectron spectroscopy, and Raman spectroscopy was a specific focus. Students also analyzed literature data to reach conclusions and determine their next steps, so the case should improve their ability to interpret data. However, students only saw one or two examples of each type of data, so the case did not include thorough data analysis for any particular technique.

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VINLAND MAP CASE

Vinland Map Background

The Vinland map appeared to be a mid-15th century Norse map that included Greenland and a large landmass west of Greenland, making it the oldest surviving map showing American lands. The map was initially authenticated by scholars at Yale University and the British Museum in 1965.11 An authentication debate followed based on both the appearance of the map and the lack of provenance, culminating in a 1966 conference bringing together scholars of cartographic Received: January 10, 2018 Revised: July 23, 2018

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DOI: 10.1021/acs.jchemed.8b00027 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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was not graded, so there was no effort to prevent student communication.

history, in which several scholars continued to question the authenticity of the map.12 The question of authentication provided the motivation for subsequent instrumental analysis. The Vinland map authentication has previously been used in several settings as an educational example. It was the subject of a Brandeis University educational website.13 It was also used as an example of applied instrumental analysis in the textbook Principles of Instrumental Analysis14 and in a summary of applications of analytical chemistry in archeology.15 However, none of these examples required students to select analytical techniques or analyze the primary-literature data. Advanced undergraduates who had completed the spectroscopy portion of an analytical-chemistry course were capable of designing and proposing experiments to test the map and could understand many of the resulting data figures. By pursuing a detailed analysis of the original data collected from the map, students saw the strengths and limitations of several analytical techniques and experienced a true controversy in the field of analytical chemistry.

Initial Chemical Analysis

Students were initially tasked with listing the analytical challenges of the case. The prompt was intentionally broad to encourage student creativity and broad discussion of the case. Following the initial discussion, students volunteered their ideas to the class. The subsequent class discussions of analytical challenges always highlighted the issues of small sample size and the need for nondestructive analytical techniques. Other topics that came up in some years included the probable oxidation and possible contamination of the samples. After listing challenges, students worked in small groups to classify each spectroscopic technique they had learned about by its level of usefulness toward the problem. Students generated lists of “very useful”, “possibly useful”, and “not appropriate” techniques. This analysis of each technique formed an effective review of spectroscopic instrumentation. Students also often developed creative reasons for placing an instrument in the “possibly useful” category, including the use UV or fluorescence active tags for the expected iron in the ink. Students also frequently related these discussions back to their laboratory experience with each instrument. The classification activity was particularly useful for the atomic spectroscopy techniques, in which the students concluded that the techniques would be very useful for elemental analysis, but the destructive nature of the techniques eliminated them from consideration. Following the initial classification of spectroscopic instruments, students were left with a list of several techniques in the “very useful” category. These techniques usually included X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectroscopy as nondestructive techniques that could be used without dissolving the solid samples. Once the students finished volunteering useful techniques, the students voted as individuals on which technique to apply first and I revealed the data relevant to their chosen technique, typically presenting a single key figure or series of figures from the literature. Although the vote was often split among the three proposed techniques, group members tended to vote together. I did not experience a tie, but I would likely resolve one in a 50 min class with a coin flip or equivalent random selection to keep the class moving quickly. Following the student vote, I projected the requested data and small-group discussions followed. The flow of the case took several forms, depending on the first technique chosen, and a flowchart of the case for each possibility is included in the Supporting Information. The most common flow of the case, occurring in two of the four offerings, began with a selection of X-ray photoelectron spectroscopy. X-ray photoelectron spectroscopy data does not exist for the samples, so I presented the energy dispersive X-ray (EDX) data for elemental analysis shown in Figure 2.18 We discussed the limitations of the EDX data and the inability to determine oxidation state. Students typically concluded that a 600-year-old map would likely have oxidized over time regardless of the original oxidation state, so the absence of that information was not limiting. EDX data revealed that although the black-ink samples contained iron as expected, the yellowed part of the ink samples contained significant amounts

Case Introduction

The case was placed at the end of the spectroscopy unit, when students had learned about the theory and applications of each spectroscopic instrument. Students were introduced to the case in a one-page handout (see the Supporting Information) that included a picture of the map, shown in Figure 1, and described a brief history of the map and the initial authentication.

Figure 1. Photograph of the Vinland map. Reprinted with permission from the Beinecke Rare Book and Manuscript Library, Yale University.16

The purpose of the handout was to introduce students to the map history and to provide some minimal non-spectroscopybased background information so the class discussions could focus on only spectroscopic techniques. Radiocarbon dating analysis from 2002 was included to show that the Vinland map parchment was authentic to the 15th century.17 Basic information about the chemical composition of the iron gall ink used in the 15th century was also given so students could compare the primary-literature results to expectations. The handout provided to students is included in the Supporting Information. An alternate prompt including only the historical background and omitting all experimental data is also included. Students worked in small groups that were not assigned, and there was typically some informal discussion between groups as they overheard each other in the classroom. The case study B



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Figure 3. X-ray powder diffraction data for Vinland map samples. Reprinted from ref 18. Copyright 1988 American Chemical Society.

Figure 2. Energy dispersive X-ray pattern for the Vinland map: (a) black ink samples and (b) yellow ink samples showing the difference in chemical composition for the two types of samples. Reprinted from ref 18. Copyright 1988 American Chemical Society.

of titanium. Comparison of the EDX data for the Vinland map and two other contemporary publications showed the titanium to be unique to the Vinland map. Students next wanted to learn more about the nature and origin of the titanium and selected X-ray diffraction to see whether the titanium was crystalline. Students were presented with the XRD data in Figure 3, which indicated the presence of anatase TiO2 in two of the samples, although the data were not definitive, and students could see that one sample included calcite (CaCO3) contamination.18 Students were generally not completely convinced by the XRD data after spending time analyzing the relative intensities for the anatase and contamination peaks. Following the XRD discussion, students elected to use the last technique from their original list, Raman spectroscopy. Raman spectroscopy in Figure 4 revealed similar results to those from X-ray diffraction; anatase TiO2 was also identified in the yellow ink from one sample.19 Students were also not overly convinced by the Raman spectroscopy, given the single sample and small peaks, but the combination of XRD and Raman demonstrated the benefits of consulting multiple techniques. The strength of the case was the flexibility of the initial analysis as the case proceeded successfully regardless of the order in which students selected the first three techniques. No single technique provided unambiguous and thorough data given the limited sample sizes and contamination, so in each offering of the case, students were engaged throughout the analysis of these first three techniques and concluded that the

Figure 4. Raman spectroscopy of Vinland map ink. The solid line shows anatase in the yellow ink; the dotted line shows the plain parchment. Reprinted from ref 19. Copyright 2002 American Chemical Society.

yellow ink was anatase-based after all three techniques were discussed. Chemical Analysis Controversy

Following the discussion and analysis of two or three techniques and an initial assessment that the ink appeared to contain anatase TiO2, students were presented with later proton induced X-ray emission (PIXE) data, including linescans of the ink, which showed the elemental composition at varying locations.20 Although PIXE is a specialized technique not typically part of an undergraduate curriculum, students were able to analyze the data resulting from this technique, and the use introduced them to the continued development of specialized analytical techniques. The PIXE data in Figure 5a indicated that the titanium attributed to the ink samples appeared to have a very low concentration that could have been due to document-wide contamination. Figure 5b showed elevated titanium levels across the ink, but still indicated relatively low titanium concentrations compared with other elements such as potassium, chlorine, and sulfur. Students compared the PIXE elemental analysis to the EDX data, which did not indicate C



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Figure 5. (a) PIXE parchment transects for titanium, zinc, and iron. The locations 114 to 138 represent a west-to-east transect across the middle of the map, whereas locations 139 to 149 represent a north-to-south transect of the “Atlantic Ocean”. (b) Transects along a single line of ink, “Japan(?)”, from east to west for total distance from 72 to 78 (3 mm). Reprinted from ref 20. Copyright 1987 American Chemical Society.

significant levels of potassium or chlorine.18 The PIXE data caused students to reconsider their conclusion of anatase TiO2 presence. The small sample sizes available meant that the XRD data supporting the finding of anatase TiO2 was limited to only two samples, and analysis of the Raman data was typically unconvincing to students because of the small peak size. I also projected selected quotes from the PIXE paper to accentuate the controversy, including this quote:20 Our results show that it is not valid to generalize about the composition of the ink as a whole from these small aliquots. When we tested dozens of ink locations throughout the map, we found that the amount of titanium in the ink is at most only 0.007% of the average amount estimated by McCrone Associates... Students were next tasked with designing control experiments to determine the reliability of the earlier results indicating the presence of an anatase-based ink. Through small-group and class discussion, students arrived at a variety of ideas for control experiments. Comparison of the titanium in the ink and the titanium in parchment samples was a common idea, and students were presented with the literature data showing that the amount of titanium in the ink was significantly higher than in the parchment in the PIXE measurements.21 Interpretation of the graph included understanding the 95% confidence level; however, the graph appearance is unusual, and the authors may have represented one-dimensional uncertainties on a two-dimensional plot. Several subsequent discussions resulted from this controversy, but eventually students returned to their list of appropriate techniques. Any technique not chosen earlier

(once Raman spectroscopy and once X-ray diffraction) was used to confirm the presence of anatase TiO2. At this point, as the case came to its conclusion, students were presented with additional information about anatase TiO2, including the three crystal structures of TiO2, the information that anatase is not the most thermodynamically stable structure, and the high-temperature processing methods typically used to form anatase. Students were challenged with designing experiments to prove that the anatase in the map could not have been produced in the Middle Ages. This final discussion often brought up many creative student ideas. Although they were unlikely to arrive at the actual technique used, students could easily understand the imaging data presented. Images of the anatase particles, and the size distribution in Figure 6, showed that the anatase in the Vinland map samples had particle-size distribution completely different from natural anatase samples and very similar to samples from modern inks. The final presentation of the inksample images and size distribution brought the case to the satisfying conclusion that the map was a forgery.

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CASE MANAGEMENT The case was used four times, in classes of 30, 48, 49, and 60 students, for a total of 187 students. The case required one 50 min class period to run, and students were expected to read a one-page handout of information before class. Students worked in groups of 3−6 for small-group discussions. Students would typically discuss a question or topic in their small groups, and then the full class would discuss the same question or topic, with students contributing the best ideas from their groups. Decisions of the next course of action were decided by a classD



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consider the applicability of separation techniques or mass spectrometry. If students were allowed more time for the case study, they could be provided with larger excerpts from the primary literature and expected to analyze data figures with their accompanying text, rather than being provided with the most relevant figures directly. For an instructor trying to fit the case study into a shorter period of time or trying to more closely guide the discussion, more direct questions in the prompt would likely streamline the discussion. For example, a direct prompt of “Should destructive or non-destructive methods be used with these samples?” would be more efficient than the broad question of “What analytical difficulties are specific to this case?” that was used in this class.

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ASSESSMENT

Initial assessment of the case consisted of student surveys at the end of the semester, asking students to identify the parts of the class in which they were “most engaged or interested”. This case study was identified as the most interesting by 20 of the 56 students surveyed. I also asked students to identify the parts of the class in which they were “least engaged or interested” and none of the students identified the case study in that section, indicating that the case study did appear to increase student interest in instrumental chemistry. The case study was performed in the first half of the course, so it was well removed from the survey. Subsequently, a peer from the biology department conducted a discussion with the same class about what things in the class most helped or hindered their learning. This discussion was part of a peer teaching exchange broadly focused on gauging interest in the course. Again, the case study was singled out as being particularly interesting. Anecdotal negative comments were also telling, because the few students who did not find the case study engaging commented that they did not know the spectroscopic techniques well enough to understand the discussion and wanted more time to review prior to the case study. These comments indicated that although the case study was enjoyable for students, it was also a challenging activity. These assessments were consistent with my perceptions as an instructor. The case study was not graded, yet students were highly engaged in the analysis in each of the four offerings. The

Figure 6. Size distribution of anatase: curve A, Vinland map sample 11-A; curve B, commercial anatase from National Lead Industries, Titanium Pigments Division; and curve C, ground mineral sample from the Smithsonian Institution. Reprinted from ref 18. Copyright 1988 American Chemical Society.

wide vote. One benefit of this case study is that it can be inserted into an existing class structure without substantial curricular disruption or class time used. The case also exposes students to primary literature and data analysis without the added complication of a laboratory component. Alternate Case Management

This case was designed to take place after a spectroscopy section in an instrumental-chemistry class in which spectroscopy was the first group of instruments covered. As a result, the prompt limited student analysis to the ink samples, and the discussion was limited to only spectroscopic instrumentation. Changes to the case could be successful in classes of students with different levels of instrumental knowledge or different amounts of time. For example, if instrumental techniques were covered in another order, students could

Table 1. Comparison of Scores for the Self-Assessment of Student Understanding of Spectroscopic-Technique Theory and Applications Average Student Response Scoresa Collected Relative to the Case Study, N = 49 Understanding of Spectroscopy Theory Spectroscopic Technique UV−vis fluorimetry IR Raman AA AE XRA XRD XPS

Before 4.3 3.6 4.1 3.4 3.8 3.7 3.1 3.1 3.2

± ± ± ± ± ± ± ± ±

0.7 0.9 0.8 0.9 0.8 0.7 0.8 0.9 0.9

Understanding of Spectroscopy Applications

After

Change

± ± ± ± ± ± ± ± ±

0.0 0.3 0.0 0.5 0.4 0.5 0.7 0.6 0.8

4.3 3.9 4.1 3.9 4.2 4.2 3.8 3.7 4.0

0.7 0.7 0.7 0.8 0.7 0.7 0.9 0.9 0.9

Before 4.3 3.8 4.2 3.8 4.2 4.1 3.5 3.5 3.5

± ± ± ± ± ± ± ± ±

0.7 0.9 0.8 0.9 0.8 0.9 1.1 1.1 1.0

After

Change

± ± ± ± ± ± ± ± ±

0.0 0.1 −0.1 0.1 0.1 0.1 0.5 0.4 0.6

4.3 3.9 4.1 3.9 4.3 4.2 4.0 3.7 4.1

0.7 0.8 0.8 1.0 0.8 0.8 1.0 1.0 0.9

a

Scores could range from 1−5, with 1 being low and 5 being high. E



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techniques that were more substantially discussed appeared to improve. Infrared and UV−visible spectroscopy were also techniques that students were relatively familiar with from their introductory classes, so their perceived level of understanding before the case study was relatively high. The absence of improvement for these techniques not covered in the case study also demonstrated that the gains were not due to overall increases in student understanding during the progression of the semester; rather, the case study provided students with improved understanding of selected techniques.

larger class sizes of 30−60 prevented participation in the classwide discussions by every student, but I walked through the room during small-group discussions and typically observed animated discussions among students. Although I was not able to determine engagement at the individual-student level, I was able to note that every group appeared engaged in the activity throughout each offering. Student comfort with the case-study technique also improved over the class period. Students routinely offered more creative ideas toward the end of the class period, and they seemed genuinely surprised that a manuscript authenticated by highly credentialed experts was found to be fraudulent. To quantitatively assess the impact of the case study on student understanding and comfort with spectroscopic techniques I surveyed student understanding and comfort applying each analytical technique before and after the case study. The survey consisted of two questions. Students were asked, “Please rate your understanding of the theory behind each spectroscopic technique,” and provided with a list of spectroscopic techniques covered in the class with a five-point Likert scale printed to the right of each technique. The second question asked students to rate their “understanding of how to apply each spectroscopic technique” followed by the same list of techniques and five-point Likert scale. The “before” surveys were administered at the end of the class before the case study and the “after” surveys were administered immediately after the case study. Table 1 reports the tabulated averages of the survey results. In cases in which students circled two numbers, the average of the two was used in tabulation. The assessment was reviewed by the Holy Cross institutional review board and was judged to be exempt from informed consent. The survey results showed the largest improvements in student understanding of both the theory and the application of the three X-ray-based techniques of X-ray absorption, Xray diffraction, and X-ray photoelectron spectroscopy. However, none of the improvements were larger than the standard deviation. Improvement in X-ray technique understanding was consistent with the student experience, in which the students primarily considered X-ray techniques following the initial conversations as they limited the analysis to nondestructive techniques. It was notable that students reported relatively large improvements in their understanding of X-ray absorption even though that was not one of the techniques used. Students did typically propose that technique for use, and I believe the improved understanding was due to the in-class consideration and rejection of the technique as lacking specificity. Similarly, students reported gains in atomic absorption and atomic emission spectroscopies, two techniques that were discussed in the initial technique considerations but rejected early in the discussion as being destructive. These results showed that it was not necessary for students to work directly with the data for each technique to report a relatively large increase in understanding. Students reported small increases or even decreases in understanding for several techniques, primarily UV−visible spectroscopy and infrared spectroscopy, both of which showed very small or negative changes in both the theory and application categories. UV−vis spectroscopy and infrared spectroscopy served as controls for the other techniques, as both were rejected as useful techniques early in the discussion. The learning goal of increasing student-perceived understanding for each technique was not achieved, and only

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CONCLUSIONS The Vinland map authentication has been a widely used example of analytical chemistry. In this paper, I show that it could be applied as a case study in an upper-level class in which students directly engage with the primary literature. Assessment of the case study showed it to be an engaging activity that also improved students’ perceived understanding of the instrumental techniques discussed.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00027. Teaching notes, flowchart of case options, student handout with background information and initial instructions, and figures projected during case use (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Elizabeth C. Landis: 0000-0001-7801-331X Notes

The author declares no competing financial interest.

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ACKNOWLEDGMENTS The author thanks Holy Cross Chem 300 students for their participation. Background on the case-study technique was gained from “Making the Case: Integrating Case Studies in Our Liberal Arts Classrooms”, a Holy Cross Center for Teaching workshop presented by Ann Velenchik.

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REFERENCES

(1) Jones, R. The Case Study Method. J. Chem. Educ. 1975, 52 (7), 460−461. (2) Herreid, C. F. Case Studies in Science − A Novel Method of Science Education. Journal of College Science Teaching 1994, 23 (4), 221−229. (3) Herreid, C. F. Confchem Conference on Case-Based Studies in Chemical Education: The Future of Case Study Teaching in Science. J. Chem. Educ. 2013, 90 (2), 256−257. (4) Herreid, C. F.; Schiller, N. A.; F, H. K.; Wright, C. In Case You Are Interested: A Survey of Case Study Teachers. J. Coll. Sci. Teach. 2011, 40, 76−80. (5) Colyer, C. L. ConfChem Conference on Case-Based Studies in Chemical Education: You (Want To) Call Yourself a Case Study Teacher? J. Chem. Educ. 2013, 90 (2), 260−261. (6) National Center for Case Study Teaching in Science. http:// sciencecases.lib.buffalo.edu/cs/ (accessed July 2018). F



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(7) Analytical Sciences Digital Library. http://home.asdlib.org/ (accessed July 2018). (8) Stenken, J. A. Adapting the Chemical Analysis of Paintings in the Context of Art Conservation to a Project-Based Learning Instrumental Analysis Laboratory. http://asdlib.org/onlineArticles/ elabware/StenkenPBLArt.pdf (accessed July 2018). (9) Epstein, M.; Bullard, M.; Buehler, B.; Kloster, R. Using Pseudoscience as an Aid to Teaching General and Analytical Chemistry. http://mikeepstein.net/path/path.html (accessed July 2018). (10) Epstein, M. S. Chemistry Everyday for Everyone Using Bad Science To Teach Good Chemistry. J. Chem. Educ. 1998, 75 (11), 1399−1404. (11) Skelton, R. A.; Marston, T. E.; Painter, G. O. The Vinland Map and the Tartar Relation; Yale University Press: New Haven, 1965. (12) Proceedings of the Vinland Map Conference; Washburn, W. E., Ed.; University of Chicago Press: Chicago, IL, 1971. (13) Henchman, M. The Vinland Map. http://vinland-map. brandeis.edu/introduction/index.php (accessed July 2018). (14) Skoog, D. A.; Holler, F. J.; Crouch, S. R. Principles of Instrumental Analysis, 6th ed.; Cengage Learning: Belmont, CA, 2007. (15) Beilby, A. L. Art, Archaeology, and Analytical Chemistry. J. Chem. Educ. 1992, 69 (6), 437−439. (16) Vinland Map; Beinecke MS 350A; Beinecke Rare Book and Manuscript Library, Yale University. (17) Donahue, D. J.; Olin, J. S.; Harbottle, G. Determination of the Radiocarbon Age of Parchment of the Vinland Map. Radiocarbon 2002, 44 (1), 45−52. (18) McCrone, W. C. The Vinland Map. Anal. Chem. 1988, 60 (10), 1009−1022. (19) Brown, K. L.; Clark, R. J. H. Analysis of Pigmentary Materials on the Vinland Map and Tartar Relation by Raman Microprobe Spectroscopy. Anal. Chem. 2002, 74 (15), 3658−3661. (20) Cahill, T. A.; Schwab, R. N.; Kusko, B. H.; Eldred, R. A.; Moller, G.; Dutschke, D.; Wick, D. L.; Pooley, A. S. The Vinland Map, Revisited: New Compositional Evidence on Its Inks and Parchment. Anal. Chem. 1987, 59, 829−833. (21) Towe, K. M. The Vinland Map: Still a Forgery. Acc. Chem. Res. 1990, 23, 84−87.

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Vinland Map Authentication: A Case Study for the Review of

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