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University of Iowa Center for the Book Graduate College

1-1-2011

Estimation of gelatin content in historical papersusing NIR spectroscopyM OrmsbyNational Archives and Records Administration

T BarrettUniversity of Iowa, timothy-barrett@uiowa.edu

J. B. LangUniversity of Iowa, joseph-lang@uiowa.edu

J. MazurekGetty Conservation Institute

M. SchillingGetty Conservation Institute

Author Posting (c) Morana RTD., 2011. This is the author's version of the work. It is posted here bypermission of the publisher for personal use, not for redistribution.

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ESTIMATION OF GELATIN CONTENT IN HISTORICAL PAPERS USING NIR

SPECTROSCOPY Running title: NIR of gelatin in historical paper Note: This MS has been accepted with minor revisions for publication in e-Preservation Science, the online conservation science journal. http://www.morana-rtd.com/e-preservationscience/ Those revisions are in place but have not yet been approved by the editors of the journal. We will provide a link to the final published version as soon as it is available. M. Ormsby1*, T. Barrett2, J.B. Lang3, J. Mazurek4, and M. Schilling4 1. National Archives and Records Administration, 8601 Adelphi Road, Room 1800, College Park, MD 20740 2. University of Iowa Center for the Book, 29 North Hall, Iowa City, IA 52242 3. University of Iowa, Dept. of Statistics and Actuarial Science, 207 Schaeffer Hall, Iowa City, IA 52242 4. The Getty Conservation Institute, 1200 Getty Center Drive, Suite 700, Los Angeles, CA 90049 * Corresponding author mark.ormsby@nara.gov ABSTRACT Gelatin sizing was a key ingredient during the handpapermaking era. The gelatin concentration in historical papers has never been well documented, however, because measuring the gelatin content required destructive sampling. In this project we developed a non-destructive method using near infrared (NIR) spectroscopy. Gelatin concentrations of 40 historical papers from the 15th-18th centuries were determined from amino acid (AA) concentrations by using gas chromatography/mass spectroscopy. These values were combined with NIR spectra from the same papers to generate a model for predicting concentrations of unknowns. If a NIR measurement predicted a gelatin concentration in the range 0-6 percent then there is a 95% probability that the difference between the NIR model value and a destructive AA measurement would be between -1.6 and +1.3 percentage points. For 6-8 percent there is a 95% probability the difference would be between -2.0 and +1.5 percentage points, and for 8-12 percent the difference is between -3.0 and +2.0 percentage points. In a study of 159 specimens from books, loose leaves, and artworks printed from 1460-1791, the means for all papers were quite high in the 15th century and dropped an average of 20% every 50 years. Possible explanations for the decline are offered.

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KEYWORDS: gelatin, sizing, paper, near infrared spectroscopy

1. INTRODUCTION William Barrow’s 1974 study of 1500 bookpapers made between 1507 and 1949 was pioneering in its analysis of historical specimens to reveal new information about paper permanence and durability.1 His study did not, however, include papers from the 1400s known to be exceptionally stable. Barrow also did not test for gelatin, a common ingredient in papers made between the 15th and the 18th century. Gelatin was added as a sizing agent to make the paper more resistant to ink bleeding, but it also strengthened the paper.2 Several researchers have provided evidence that gelatin may promote paper stability. Dupont showed that gelatin has a significant role in reducing degradation induced by papermakers’ alum.3 However, the gelatin-sized papers also had more discoloration and lower pH after accelerated aging. Kolbe demonstrated that gelatin can bind free iron(II) ions in unbalanced iron-gall inks that can catalyze oxidative degradation.4 Copper can also catalyze oxidative decay, and Kolar et al. found high copper contents in some historic inks.5 As with iron(II) ions, gelatin is able to bind copper, as demonstrated in research on the oxidation of sulfur dioxide in gelatin.6 Baty and Barrett confirmed gelatin’s anticipated ability to act as a pH buffer in paper.7 They also documented the higher moisture holding capacity of a gelatin sized paper compared with an unsized control, although the net impact of this latter effect on paper permanence and durability is unknown. The current project builds on Barrett and Mosier’s 1995 research which analyzed the gelatin concentration in a group of 35 historical papers using a destructive, industrial method to quantify the glue in paper.8 They found a relationship (although not a strong one) between lighter color on the one hand, and increased gelatin and calcium content and higher pH, on the other. The resulting set of paper specimens with known gelatin content were set aside for use in the future development of non-destructive gelatin measurement techniques. This was the only method future researchers could use to undertake a much broader study of 15th century papers in exceptional condition and compare them with papers made in subsequent centuries when paper quality declined. Lang et al. used this set of 35 papers to explore the use of attenuated total reflectance mid-infrared spectroscopy for this purpose,9 and other work on these same specimens used reflectance measurements.10 In both cases, the accuracy of the non-destructive methods was less than desired. Subsequent tests showed promising results with near-infrared (NIR) spectroscopy.11 These earlier studies led to the current project.

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2. EXPERIMENTAL Data were collected with an Analytical Spectral Devices LabSpec Pro UV/VIS/NIR spectrometer. A LabSpec Pro reflectance probe with a standoff reflectance accessory

collected spectra over a circular area about 5 mm in diameter. The accessory holds the probe at approximately 70 degrees relative to the surface of the specimen, with the probe lens approximately 4 cm from the document The accessory has a window which allows the specimen to be viewed and assists in positioning the probe. Preliminary tests indicated that room lights did not affect the spectra from specimens. Spectra were gathered over a range of 350-2500 nm at 1 nm intervals. A Spectralon® (pressed polytetrafluoroethylene) disk was used as the white reflectance standard. The system was calibrated at the beginning of each data collection period. Preliminary tests were made by taking spectra with no support behind the sample area and then repeating the measurements with the specimen placed on a metal plate. The tests showed significant differences in absorbance between these spectra as a function of wavelength, indicating that the entire thickness of the sheet was being sampled, not just the surface. To provide a uniform and consistent background the specimens were placed on top of a Gore-tex® sheet. Used for conservation treatments, the sheet is a laminate of expanded polytetrafluoroethylene bonded to a non-woven polyester felt.12 The flexible sheet can be inserted between pages of a book to provide the background for collecting spectra. In earlier mid-IR and NIR work the models were calibrated using the gelatin concentrations determined by Barrett and Mosier in 1995. They employed Technical Association of the Pulp and Paper Industry (TAPPI) Method T504a, a wet chemical procedure which measures the concentration of hydroxyproline, an AA present in gelatin.13 Not only is this method difficult and time-consuming, but the results also suffered from large standard deviations, particularly at the higher concentrations. As a result of these limitations, gelatin concentration predictions based on these earlier models were less precise than desired. For the current project, the gelatin concentrations in a new set of 40 historical specimens were measured by removing samples of paper and analyzing them as ethyl chloroformate derivatives using gas chromatography/mass spectroscopy (GC/MS). Developed by Schilling and Khanjian,14, 15 this method has been used extensively in paintings conservation for binding media analysis. In contrast to the TAPPI method, the GC/MS approach quantifies gelatin based on seven amino acids, not just hydroxyproline. Of the 40 historical specimens, half were categorized as light and half as dark. Some specimens whose gelatin content was previously measured by the TAPPI method were selected to attempt to include a broad range of gelatin concentrations. Table I lists the specimens and their date of manufacture along with the analysis results. Grammage measurements were made on the air-dry (AD) specimens without preconditioning or conditioning.

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Table I: Historical specimens used to develop NIR model

Historical Specimens with weight percent gelatin based on 7 AA concentrations as determined by GC/MS. “Est.” grammages were approximated due to voids from previously removed sample material. Note: Some attributions require additional research/clarification. WB = William Barrow Laboratory ID number. TB = Barrett ID number from previous research or other identification information. ID

#

ID Year City or

Country

Grams/

Meter2

Gelatin

% w/w

(average

of 3)

std.

dev.

of

gelatin

% w/w

D1 T. Warton. The History of English Poetry TB UI Coll.

1764 London 86 1.36 0.12

D2 J. Busaeus. Arca medica variis divinae scripturae. WB 1484

1608 Monguntiae 54 0.14 0.03

D3 P. Francii. Oratio in Funere TB UI Coll. (from T. Cains)

1695 Amsterdam 104 3.10 0.15

D4 J. Ogilvie. Poems on Several Subjects. Vol. II. TB UI Coll.

1769 London 76 3.25 0.10

D5 T. Percival. Essays Medical and Experimental. TB UI Coll.

1772 London 94 3.02 0.18

D6 De Convulsionibus. TB UI Coll. (from R. Espinosa)

1749 Paris 77 3.73 0.14

D7 Bishop Burnet’s history. WB 1170

1734 London 68 2.31 0.11

D8 P. Gregorie. Opera Omnia ad Jus Ponfificum spectantia. WB 1382

1645 Geneva 59 0.13 0.04

D9 A. Mincucci. De Feudis libri sex. TB W35, WB 1269

1695 Strasbourg 66 0.13 0.01

D10 B. Romans. Annals of 1778 Conn./USA 61 1.84 0.03

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the troubles in the Netherlands. V.1. TB T91, WB 1052

D11 The law of the covenants. WB 1214

1711 Savoy 59 1.54 0.15

D12 Unprinted leaf watermarked “1757” (from S. Patri)

1757 unknown 75 3.44 0.26

D13 Feltwell. “Printed in London, 1739” TB UI Coll. (from R. Espinosa)

1739 London 76 4.68 0.39

D14 R. P. F. Joannis Nider Ordinis Praedicatorum Theologi De Reformatione Religiosorum. WB 1452

1611 Antwerp 80 4.22 0.10

D15 The humble and modest inquiry. TB P97, WB 1158

1733 Edinburgh 71 1.89 0.17

D16 J. Burrow. Reports of cases. V. 1. TB P72, WB 1019

1793 London 81 1.01 0.22

D17 H. Wolf. In Ciceronis Officia. WB 1523

1584 Basel 73 3.37 0.17

D18 The eleventh part of the reports Sir Edward Coke, Kt. WB 1187

1727 Savoy 83 1.22 0.07

D19 Monsieur l’Abbe. Histoire des guerres civiles. V.2. TB T99, WB 1101

1757 Amsterdam 98 2.98 0.45

D20 Plutarch. Plutarchi….quae exstant omnia. TB 45, WB 1512

1599 Frankfurt 71 0.86 0.08

L1 Biblia Latina. Nicolaus Jenson, BMLV 180, Goff B563

1479 Venice 91 4.54 0.39

L2 Blondus. Angelum Britannici Press. Roman History

1503 ? 85 6.66 0.10

L3 James McBey Collection of Watermarked Paper, Specimen 18

1770? Spain 81 8.94 0.93

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L4 Anno Regni Georgii Regis (from R. Lieberman)

1723 London 72 3.24 0.71

L5 The Muses Library; or a series of English Poetry, TB UI Coll.

1737 London 98 2.02 0.07

L6 Politanus Opera, Aldus, UI SC PL

1498 Venice 96 4.55 0.57

L7 Johannes Antonius Campnus Opera, Printed by E. Silber, TB G15

1495 Rome 88 4.98 0.58

L8 Jean de Charlier de Gerson. Goff G186, TB UI SC Griffin

1488 Strasbourg 81 8.44 1.04

L9 Blondus, Flavius. Historium AB Inclinatione. Printed by O. Scotus

1483 Venice 100 4.90 0.52

L10R

M. Velleii. Paterculix Que Supersunt: WB 1208

1711 Oxford? 78 2.18 0.19

L11R

Bible, (In German). Zainer, UI SC PL duplicate

1477 Augsburg 103 5.07 0.35

L12 Horatius Flaccus. Guintus Opera. TB G14

1482 Florence 80 est. 7.78 0.83

L13 Blank leave with three hills watermark TB G17, (from R. Espinosa)

1400s Italian? 81 est. 11.36 0.38

L14 F. Biondi. L’istoria delleverrecivili. D’inghilterra tra le due cafe di lancaftro e iorc. TB 146, WB 1379

1641 Venice 109 3.71 0.14

L15 A narrative of the proceedings of the lower house of convocation. TB T2, WB 1239

1701 London 66 6.76 0.56

L16 The fifth part of the reports of Sr. Edward Coke Knight. TB T165, WB 1340

1660 London 83 4.38 1.16

L17 James McBey 1700s ? 89 4.76 0.15

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Collection of Watermarked Paper, Specimen 32, TB T25

L18 Antonius De Bitonto. Sermones Quadragesimale De Vitiis. TB G/T16

1499 Venice 75 10.84 0.22

L19 The history of the reign of Henry the Fifth. TB T3, WB 1245

1704 London 79 3.43 0.53

L20 T. Aquinatis. Johannes Capreolus Defensionum Theologia. TB G/T12

1483 Venice 87 6.43 0.37

For the AA analysis, a Whatman Harris micropunch was used to remove circular samples 1.2 mm in diameter from 10 locations distributed over each specimen. Areas with ink or stains were avoided. Material was punched equally from the 10 different locations sufficient to generate 3 samples of 5 mg each AD weight as was required for triplicate GC/MS analyses. NIR spectra were taken as close as possible to the 10 sampling locations on each specimen. Data were collected on both sides of the sheet, so a total of 20 spectra were gathered from a specimen during a given data collection session. To study the repeatability of the measurements and simulate use in the field, a second set of 20 spectra was gathered on another day. Between sessions the system was powered down, and the reflectance probe and fiber optic connections were disassembled. The same procedure was followed for a third session, so a total of 60 spectra were gathered from each specimen. Figure 1 shows the average of these 60 spectra for each of the 40 historic specimens.

Figure 1: Spectra from 40 historic specimens

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These spectra were collected with the instrument in an environmentally-controlled room with temperature 22° C and relative humidity (RH) 50-58%. The specimens were stored in the room between analysis sessions. When the instrument is used in the field in archives, libraries, museums, and other environments, the RH may vary considerably. To study the effect of this variable, a few specimens were placed in desiccators at 20-25% RH and allowed to equilibrate for at least one day. A specimen was then removed, immediately placed on the sampling stage, and analyzed by collecting spectra at 10-15 second intervals over the next 10-15 minutes as the paper responded to the ambient environment of 50-55% RH. Figure 2 shows a typical result with the greatest response in the range 1900-2000 nm.

Figure 2: Response of specimen to changing RH

3. RESULTS The averaged spectra from the 40 specimens and the gelatin concentrations determined by the GC/MS method were analyzed with Grams/PLSplus IQ chemometric software. The model used partial least squares with leave one-out cross-validation. Figure 3 shows the mean centered, first derivative of these spectra calculated using the gap method with spacing 15. Based on the prediction residual error sum of squares plot and F-ratio values,16 a model was selected utilizing four factors and the wavelength ranges highlighted in blue in Figure 3. The region near 1900-2000 nm was excluded in an attempt to reduce sensitivity to differences in moisture content caused by variations in RH when the equipment is used in the field. In future work it might be possible to incorporate the response as a function of RH into the model and to predict the moisture content of the specimen.

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Figure 3: Processing of spectra to develop model The UV and visible ranges were not used because various tests indicated that they introduced more noise without improving the model. Missori et al., demonstrated the effects of gelatin sizing on the reflectance of paper, 17 and it was expected that including the UV-VIS range would enhance the model. The relatively poor sensitivity of the system in the UV range may explain the results in that region. While including portions of the visible range may have improved the model marginally, those wavelengths were not added because of the wide scatter of the first derivative spectra (Figure 3). To take advantage of the information contained in the UV-VIS range it would be helpful to have a larger set of historical specimens and perhaps to try different chemometric analysis methods. For example, Cséfalvayová et al. used 96 papers from the 17th to the 19th century and employed a genetic algorithm to develop the chemometric model.18 Figure 4 shows the results of the new model using the 40 specimens. The horizontal axis is the percent by weight of gelatin as measured by the destructive GC/MS AA analysis, and the vertical axis is the percent gelatin as predicted by the cross-validated NIR model. The error bars show one standard deviation calculated from the triplicate GC/MS measurements. The standard error of cross validation16 (SECV) was 0.74.

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Figure 4: Predicted vs. actual comparison While the R-squared and SECV values give some indication of how well the NIR model fits the calibration data, these quantities do not take into account the uncertainties in the AA measurements, which are illustrated by the horizontal error bars in Figure 4. Various methods have been proposed for incorporating reference value uncertainties into the chemometric modeling process,19-21 and the topic is under active development in the field.

For this study, the size of the reference value uncertainty was evaluated compared to the standard deviation of the NIR predictions. As discussed above, in developing the model 10 spectra were collected from both sides of a reference specimen during a given data collection session. The average of each set of 10 was calculated for all 3 sessions, yielding 6 spectra per specimen. These averaged spectra yielded 6 gelatin predictions. Figure 5 compares the size of standard deviation of these 6 NIR predictions with the standard deviation of the AA measurements. For the majority of specimens with gelatin concentrations below 6%, the standard deviation of the NIR prediction is significantly larger than the standard deviation of the AA measurement. Above 6% the standard deviations are comparable, with a few exceptions. Overall, the standard deviation of the replicate NIR readings is a reasonable approximation of the uncertainty in the gelatin prediction. That is, the uncertainties in the AA values are assumed to be negligible relative to the standard deviation of the NIR readings. As is clear from Figure 5 and discussed further below, this approximation is less accurate at higher concentrations (8% and above), and the accuracy of the model could be improved by adding more calibration specimens in this range. Future work could also incorporate the techniques discussed in references 19-21.

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Figure 5. Comparison of standard deviation of replicate NIR measurements and AA data The data from Figure 4 are re-plotted in Figure 6, but all replicate predictions are shown instead of the average. The outer lines are the 95% prediction intervals based on the repeatability of the measurements. Figure 7 illustrates the same data, but for clarity the vertical axis shows the difference between the concentration predicted by the NIR model and the GC/MS AA measurement. Again, the outer lines are the 95% prediction intervals. Based on these results, if the NIR measurement on a specimen predicted a gelatin concentration in the range 0 to 6 percent then there is a 95% probability that the difference between the NIR model value and a destructive AA measurement would be between -1.6 and +1.3 percentage points. For example, if the NIR value was 5.0, there is about a 95% chance the AA measurement would be between 3.4 and 6.3 percent. Between 6 and 8 percent gelatin there is a 95% probability the difference between the two measurements will be between -2.0 and +1.5 percentage points, and between 8 and 12 percent the difference is between -3.0 and +2.0 percentage points. We found no statistically significant difference in the gelatin concentration on the front versus the back of the specimens.

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Figure 6: Data from repeatability tests

Figure 7: Difference between model and AA results At the higher concentrations the model is less accurate in part because there are fewer calibration points in this range. In future work we hope to refine the model by including more specimens at the upper levels. In addition, at higher concentrations there may be limitations in the water extraction procedure used to quantitatively extract the gelatin from the paper for subsequent AA analysis. These difficulties may account for the wider error bars on some points at higher levels in Figure 4 (although the relative standard deviation of these points is comparable to that at lower levels). To address this issue, preliminary studies were made using a combustion analysis technique on the papers to

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avoid the need for water extraction of the gelatin. Nitrogen values obtained using this method were used to calculate percent gelatin values. Unfortunately, inconsistent agreement with the AA-derived data suggested that some specimens had nitrogen- containing compounds other than gelatin present. The model discussed above was used to study the gelatin content of 159 specimens selected from books, loose leaves, and works of art printed between 1460 and 1791. With few exceptions, the 86 papers from 1460 to 1499 were in excellent condition. The 73 papers made after 1500 were in a range of condition from excellent to poor. NIR scans of these specimens were collected with an Analytical Spectral Devices QualitySpec Pro UV/VIS/NIR spectrophotometer. This instrument is identical to the LabSpec Pro instrument used for the modeling study except for the LabSpec Pro’s optional battery-powered operation for use in the field. During tests of agreement between the instruments using reference specimens, an offset of 0.5 in the gelatin prediction was found. If a correction was applied to the original data shown in Figure 8, the placement of all data points and trend lines would shift upward 0.5% on the vertical gelatin scale, but the conclusions about changes over time would not be altered. Subsequent testing following this work factored in the 0.5 correction. On each specimen 8 spectra were collected and then averaged. The gelatin content was calculated by the model using this average spectrum. The results are shown in Figure 8 where the gelatin concentration is plotted versus the year of printing. The blue line gives the maximum likelihood estimates of the means based on a log-linear Normal errors model. The black dashed lines give the 95% confidence intervals for the means. The computations were carried out using the “glm()” function in the R software language.22 Based on this model, the mean gelatin content for all papers tested dropped an average of 20% every 50 years. With 95% confidence, plausible values for this 50 year drop are between 16.6% and 23.4%.

Figure 8: Gelatin concentration over time

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4. DISCUSSION It appears that the gelatin concentration in paper dropped significantly after 1500, which coincides with the widely observed overall decline in paper quality. Why would this be the case? One possible explanation is that European paper made prior to 1500 was designed to imitate parchment in its writing, handling and working properties. The only way to achieve these characteristics in paper made from old linen and hempen rags was with high levels of gelatin sizing. Therefore, fairly heavy gelatin sizing likely persisted into the end of the 15th century out of tradition. But after 1500 things changed quickly. With the rapid spread of printing, sizing concentration dropped off, possibly due to requests from the printers to decrease sizing amounts to ease their dampening work before printing. The resulting decrease in size required would have been welcomed by the papermaker due to the reduction in work and expense. Szirmai argues that by the late 15th century, papermakers were in fact supplying unsized paper to the printers, and it was the binders who applied the size later.23

Bookbinders may have gone to the trouble of this added step because the paper was otherwise too weak to withstand binding and end use by readers. Regardless of who applied the gelatin to the paper, around 1500 there was also likely a changing perception that paper was no longer a substitute for parchment, but an entirely different and cheaper material in its own right. Figure 8 represents data on only 159 items. In order to be more confident that the apparent decline in gelatin concentration is representative of what actually happened between the 15th and the 18th centuries, an analysis of a much larger sample group is required. Such a survey is now underway as a result of the development of this technique and a recent grant from the Institute for Museum and Library Services Conservation Support Program. A total of over 1,500 specimens will be analyzed using NIR as well as x-ray fluorescence methods. In addition, we hope to refine the NIR gelatin model by obtaining more calibration points at the higher concentrations (8 percent and above) where it is less accurate. Advanced chemometrics techniques, such as used by Cséfalvayová et al.,18 may also improve the model. We are also investigating using the full UV-VIS-NIR range of the spectra gathered with this instrumentation to measure relative differences in paper color and to predict certain strength characteristics. Other researchers have also demonstrated that NIR has great potential for non-destructive analysis of paper, both handmade historic specimens and more modern machine-made

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papers. By using a very large calibration set of over 1,500 specimens dating from 1650 to 1990, Strlic et al. developed chemometric models for gelatin, pH, lignin content, degree of polymerization, and other properties as part of the SurveNIR project.24 Because our focus was on the gelatin content, our calibration set included the mid 15th to the mid 17th century period, and in subsequent testing of unknowns we were able to document very high gelatin concentrations in papers made before 1500. 5. CONCLUSIONS This study has demonstrated that NIR chemometric modeling can be used to non-destructively measure the gelatin content of historic paper specimens. Compared to our earlier efforts, the current approach is more accurate, in part because of the better calibration data provided by the GC/MS analysis of AAs. A small scale survey using this method showed a significant decrease in the concentration of gelatin after the start of the 16th century. Future efforts will expand this survey and also aim to refine the model to more accurately predict gelatin concentration, particularly at the higher concentration ranges. ACKNOWLEDGEMENTS We thank the following organizations for their support for this research: The Samuel J. Kress Foundation, the University of Iowa Office of the Vice President for Research, Analytical Spectral Devices, the National Archives and Records Administration Preservation Programs, and the Getty Conservation Institute. This research was funded in part by an Institute for Museum and Library Services Conservation Project Support (Research) Grant to the University of Iowa Museum of Art, Timothy Barrett Principal Investigator. Project Title “Analysis of 15th-19th Century Papers Using Non-destructive Techniques,” May 2007. REFERENCES 1. W. J. Barrow Research Laboratory, Inc., Permanence/durability of the book, Vol. 7, Physical and chemical properties of book papers 1507–1949, W. J. Barrow Research Laboratory, Inc., Richmond, Virginia, 1974. 2. T. Barrett, Early European Papers/Contemporary Conservation Papers, The Paper Conservator, 1989, Vol. 13.

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3. A.L. Dupont, Gelatine sizing of paper and its impact on the degradation of cellulose

during aging: A study using size-exclusion chromatograph, PhD dissertation, Universiteit van Amsterdam, Amsterdam, 2003. 4. G. Kolbe, Gelatin in historical paper production and as an inhibiting agent of iron-

gall ink corrosion on paper, Restaurator, 2004, 25, 26-39. 5. J. Kolar, M. Strlič, M. Budnar, J. Malešič, V. S. Šelih, and J. Simčič, Stabilization of

corrosive iron-gall inks, Acta Chimica Slovenia, 2003, 50, 763–770. 6. D.J. Bowden and P. Brimblecombe, The rate of metal catalyzed oxidation of sulfur

dioxide in collagen surrogates, J. Cultural Heritage, 2003, 4(2), 137-47. 7. J. Baty and T. Barrett, Gelatin size as a pH and moisture content buffer in paper, J. American Institute for Conservation, 2007, 46, 105–121. 8. T.D. Barrett and C. Mosier. The role of gelatin in paper permanence, J. American Institute for Conservation, 1995, 34, 173-186. 9. P. Lang, J. Cook, B. Fuller-Morris, S. Cullison, S. Telles and T. Barrett, Characterization of Historic Papers Using Attenuated Total Reflection Infrared

Spectroscopy, Applied Spectroscopy, 1998, 52(5), 713-716. 10. M. Ormsby, Methods for analyzing the gelatin content of historical papers, Presentation at Eastern Analytical Symposium, Atlantic City, NJ, 2001. 11. M. Ormsby and T. Barrett. Quantitative measurements of the gelatin content of historic papers using mid-IR and NIR. Poster presented at Fifth International Infrared and Raman Users Group Conference, Los Angeles, CA, 2002. 12. N. Purinton and S. Filter. Gore-Tex: an introduction to the material and treatments, in Book and Paper Group Annual, vol. 11, American Institute for Conservation, Washington, D.C., 1992, 11-13, http://aic.stanford.edu/sg/bpg/annual/v11/bp11-33.html (accessed 8-4-2008). 13. TAPPI. 1991a. Glue in paper (qualitative and quantitative determination). T504 om-

89. in TAPPI Test Methods, Technical Association of the Pulp and Paper Industry, Atlanta, Georgia, 1991. 14. M.R. Schilling and H.P. Khanjian, Gas chromatographic analysis of amino acids as

ethyl chloroformate derivatives, J. American Institute for Conservation, 1996, 35(1), 45-59. 15. M.R. Schilling and H.P. Khanjian. Gas chromatographic analysis of amino acids as

ethyl chloroformate derivatives: Part 2, effects of pigments and accelerated aging on the

Page 17 Ormsby et al.

identification of proteinaceous binding media, J. American Institute for Conservation,

1996, 35(2), 123–144. 16. R. Kramer, Chemometric Techniques for Quantitative Analysis. Marcel Dekker, Inc., New York, 1998 17. M. Missori, M. Righini, and A.L. Dupont. Gelatine sizing and discoloration: A

comparative study of optical spectra obtained from ancient and artificially aged modern

papers, Optics Communications, 2006, 263(2), 289-294. 18. L. Cséfalvayová, M. Strlič, M. Pelikan, I.K. Cigić, and J. Kolar, Determination of

gelatine in historic rag papers based on NIR/chemometrics, in Durability of Paper and Writing 2, 2008, 71-72, http://www.paperdurability.org/prog.html (accessed 8-4-08). 19. A.C. Olivieri, N.M. Faber, J. Ferré, R. Boqué, J.H. Kalivas, and H. Mark, Uncertainty estimation and figures of merit for multivariate calibration, Pure and Applied Chemistry, 2006, 78(3), 633-661. 20. J.A. Fernandez Pierna, L. Jin, F. Wahl, N.M. Faber, and D.L. Massart, Estimation of partial least squares regression prediction uncertainty when the reference

values carry a sizeable measurement error, Chemometrics and Intelligent Laboratory Systems, 2003, 65(2), 281-291. 21. M.L. Griffiths and S.L.R. Ellison, A simple numerical method of estimating the

contribution of reference value uncertainties to sample-specific uncertainties in

multivariate regression, Chemometrics and Intelligent Laboratory Systems, 2006, 83(2), 133-138. 22. R. Ihaka and R. Gentleman, R: A language for data analysis and graphics, J. Computational Graphics and Statistics, 1996, 5, 299-314. 23. J. A. Szirmai, The Archeology of Medieval Bookbinding. Ashgate Publishing, Aldershot, England and Brookfield, Vermont, 1999. Xvi, 352 pp. 24. M. Strlič, D. Lichtblau, J. Kolar, T. Trafela, L. Cséfalvayová, M. Anders, G. de Bruin, B. Knight, G. Martin, J. Palm, N. Selmani, and M. Christensen. SurveNIR project

– a dedicated instrument for collection surveys, in Durability of Paper and Writing 2, 2008, 9-10, http://www.paperdurability.org/prog.html (accessed 5-31-11).