EFFECTS OF ERASER TREATMENT ON PAPER
E. J. Pearlstein, D. Cabelli, A. King, & N. Indictor
ABSTRACT—In the first part of this investigation, the composition and aging behavior of four dry cleaning products (Opaline Pad, Pink Pearl, Magic Rub, and Kneaded Rubber erasers) are studied. The second part consists of an examination of the effects on paper of eraser treatments performed with these products. Changes in folding endurance, tensile strength, surface pH, color, texture, and wettability of aged and unaged samples of Whatman Chromatography paper treated with the four dry cleaning products were observed and are compared with results for untreated controls.Conclusions are that the dry cleaning procedures performed with these products alter surface characteristics but not mechanical properties of the paper. Pink Pearl and Kneaded Rubber erasers altered the paper surface the most while the Magic Rub eraser altered it the least. The Magic Rub eraser was determined to have substantially different organic constituents from the other three products, which have similarities in composition.
A PRELIMINARY TREATMENT for cleaning paper is often the use of a dry cleaning device, such as an eraser or crumbs, to remove surface dirt. Dry cleaning devices might be used when the paper or media cannot withstand aqueous treatment, or prior to aqueous or solvent treatments which could set unremoved particulate dirt. What has remained unknown to the conservator about these dry cleaning products is what they consist of and whether they have any deleterious effects on paper.
The question of whether eraser residues remaining in paper might prove harmful was addressed in 1966, when the Library Technology Program of the American Library Association commissioned the McCrone Associates to study seventeen book cleaning materials.1 The materials tested for use on paper were all deemed safe. It was postulated that the residue from some dry cleaning products would even be beneficial if left on the paper.2 This study suffers from a lack of description of how the erasers were used, and it therefore remained difficult to evaluate the results. Paul Banks, in a 1969 article on paper cleaning, urged the removal of dry cleaning residue from papers because of the possible long term destructive effect of eraser crumbs.3
Surface abrasion to papers subjected to dry cleaning has been studied by Kerry McInnis.4 McInnis was interested in whether sizing protected aged and unaged papers from the abrasive action of various dry cleaning products. In addition to the conclusion that sizing did serve this protective function, the erasers were ranked for relative abrasion of the paper surface and for the amount of residual crumbs deposited among the fibers.5
The current study is designed to evaluate four dry cleaning products and their effects on both the surface and mechanical properties of paper. The products tested appear in Table I, along with manufacturers' indications of composition. In Part I, the composition and aging properties of the erasers alone are described. In Part II, eraser treatments are performed on preaged and unaged paper samples followed by different postaging times. Strength properties and optical properties were examined and compared to untreated control samples.
Table I Dry Cleaning Materials Examined
2 PART I. ERASER COMPOSITIONS AND PROPERTIES
Information on the composition of the Magic Rub, Pink Pearl, Kneaded Rubber, and Art Gum erasers and the Opaline Pad was obtained from product literature and from communication with scientists employed by eraser manufacturers (Table I). The infra-red spectra of the Magic Rub, Pink Pearl, Kneaded Rubber, and Art Gum erasers and Opaline Pad crumbs were obtained to confirm the presence of the organic constituents indicated by the manufacturers. A Perkin Elmer 283 B infrared spectrophotometer with infrared data station was used.
The Art Gum and Pink Pearl erasers and Opaline Pad crumbs were dissolved in a warm acetone/hexane mixture. The Kneaded Rubber eraser was dissolved in chloroform, and the Magic Rub eraser in ethyl acetate. The residues after solvent evaporation were either deposited onto AgCl plates or pressed into KBr plates.
All but the Opaline Pad were dry oven aged separately in a Precision Scientific Company Model 17 Oven at 100 ± 2°C for 7 days. The organic constituent of the Opaline Pad is identical to that of the Art Gum eraser; this eraser was therefore used for aging experiments since volume changes could be more easily determined.
Differences in color, weight, volume, surface pH, and UV fluorescence were noted, along with any other changes that appeared significant. Colors, recorded using the Munsell system,6 were observed in a Macbeth Spectralight light box set at maximum brightness of the daylight setting. Dimensional changes were determined by measurement before and after aging with Spi 30–415 calipers, Dial type 6932. A Mettler H72 balance was used for weighing. Surface pH measurements were made using a Beckman Expandomatic SS-2 pH meter with an Ingold glass electrode. The UV fluorescence was observed in the Macbeth Spectralight light box at maximum intensity of the UV setting. The results of the observation of aged and unaged erasers and papers by UV fluorescence will be discussed together in Part II.
Communications revealed that the Art Gum eraser and Opaline Pad crumbs, as well as over 90 brands of gum erasers and two other brands of dry cleaning pads, are manufactured by one manufacturer.7 They are said to consist of vegetable oil vulcanized, or cross-linked, with sulfur bonds. Vulcanized vegetable oil is known industrially as factice. The IR spectra of Art Gum and Opaline Pad crumbs are identical to that of factice. Magnesium silicate is added to dry cleaning pads to facilitate movement of the eraser crumbs through the bag pores.7
Though additional ingredients were also reported, the spectra of the Pink Pearl and Kneaded Rubber erasers showed that factice is the major organic constituent. The presence of soluble material in the erasers corresponding to the known spectrum of factice suggests that substantial organic material in factice is not crosslinked. The Pink Pearl eraser is also said to contain rubber, antioxidants, softeners, pumice, and coloring agents. Less product information was available on the Eberhard Faber Kneaded Rubber eraser than on Faber-Castell's Kneadable Eraser. The composition of the latter is included here, though it is the Eberhard Faber Kneaded Rubber Eraser which was used and tested throughout this report. Like the Pink Pearl eraser, the Faber-Castell Kneadable eraser is said to contain factice, rubber, antioxidants, pumice, and colorants. Unlike the Pink Pearl, it is said to contain mineral oil as a softener to prevent curing, and CaCO3 as a filler.
The Magic Rub eraser proved to be significantly different in composition from the other erasers. The manufacturer reported its composition to be 30% by weight poly (vinyl chloride), 35% CaCO3 as a filler, and 35% dioctyl phthalate as a plasticizer. The spectrum of the Magic Rub is dominated by the dioctyl phthalate, suggesting that the poly (vinyl chloride) is crosslinked and hence insoluble.
The results of the aging behavior of the erasers appear in Table II. After oven aging at 100 ± 2°C for 7 days, the Art Gum eraser lost 10% of its weight and 6.3% of its volume. The color change was extreme, from an ochre (Munsell 10 YR 7/8) to a deep brown (10 YR 3/4). The eraser emitted a pungent odor. The Kneaded Rubber eraser after identical aging lost 4% of its weight and 10% of its volume. It emitted a rubber odor and turned warmer in color, from Munsell 7.5 BG 6/0 to 5 GY 6/0. It also became firmer in texture than an unaged Kneaded Rubber eraser. The Pink Pearl eraser also emitted a rubber odor upon aging and lost 2% of its weight, but gained 23% in volume. The large decrease in density of this sample suggests that decomposition products from the oven aging are entrapped in the eraser network. The color grayed slightly, from Munsell 5R 7/8 to 5R 7/6, and the surface of the eraser took on a granular appearance. After heating, the Magic Rub eraser remained dimensionally stable. It did, however, take on a warmer, grayer appearance (Munsell 5Y 9/1 to 7, 5Y 9/2), become soft and sticky, and emit an odor. This eraser remained slightly more flexible and continued to emit an odor even after cooling to room temperature.
Table II AgingaBehavior of Erasers
Surface pH of the erasers was measured before and after oven aging. After oven aging, all erasers remained within approximately 1 pH unit of their original value. The Pink Pearl was the most alkaline. The unaged Magic Rub eraser was neutral and it became slightly acid upon aging. Both the Kneaded Rubber and Art Gum erasers were slightly acid both before and after aging.
3 PART II. ERASER TREATMENTS ON PAPER
All paper samples were ½″ × 6″ strips, cut from the same roll of Whatman Chromatography paper number 1, basis weight 87 g/m2, thickness 0.16 MM., medium flow rate, supplied in ½″ by 300′ rolls. Whatman Chromatography 1 is a 100% cotton paper, manufactured without fillers and with constant thickness.8 Test data for artificially aged untreated paper are given in Table III. The dry cleaning materials used for treatments were the Magic Rub, Pink Pearl, and Kneaded Rubber erasers and the Opaline Pad. For erasing, the Whatman papers were individually tacked at each end to a piece of Fome-Cor covered with a sheet of mylar which was changed between erasers. All eraser treatments were performed on the felt side of the paper.9
Table III Physical Propertiesa of Untreated, Artificially Agedb Whatman Paper
The Magic Rub and Pink Pearl erasers were used by angling the erasers so that an edge was in contact with the total width of the paper strip. These erasers were pulled at equal pressure five times along the 6″ length of the paper and five times with some overlap along the ½″ width of the paper. In order to maintain as consistent an experimental procedure as possible, the Kneaded Rubber was handled first to soften, and then an edge was formed to perform approximately the action just described. It was thought that the use of the Kneaded Rubber eraser as a tamping device might disturb the paper surface less; however, McInnis used it in that way and still found it abrasive to the paper surface.4 The Opaline Pad was used by squeezing the bag to emit some of the crumbs, and by using the pad to rub five times along both the length and width of each paper.
Half of the treated samples were subjected to removal of the eraser crumbs by brushing along the length of the paper with a Japanese brush, 3½″ wide and with 1½″ bristles, until crumbs were no longer visible to the naked eye. This frequently included brushing crumbs off the untreated side of the paper. On the rest of the samples, there was no attempt to remove whatever eraser crumbs were deposited by the described treatment.
Paper samples were artificially aged by dry oven aging both before and after eraser treatments. Aging took place in a circulating dry air oven at 100°C. The aging categories for treated and untreated samples were as follows: unaged, aged for 7 days prior to treatment with erasers (preaged), aged for 7 days after treatment with erasers (post-aged), aged for 7 days prior to treatment and 7 days after treatment with erasers (pre- and post-aged), and aged 16 days after treatment with erasers (post-aged 16 days). All samples were equilibrated prior to testing in a constant temperature and humidity room. The range of conditions during this set of analyses was 18 ± 1°C and 34 ± 6% RH.
Two sets of photomicrographs were taken to record both the eraser particulate in the paper and the surface abrasion. Photomicrographs were taken using an Olympus OM-1 camera and an Olympus 202028 stage microscope, connected by an Olympus adaptor. In the first set, magnification was 33.3, and transmitted light was from an Olympus lamp 256667 connected to a rheostat and set up for Köhler illumination.10 In the second set of photomicrographs, magnification was 13.2 and raking light was from 2 Tensor lamps.11
3.1.4 Folding Endurance12
All paper samples were tested for folding endurance on a Tinius-Olsen Model Number 2 instrument (M. I. T. Folding Tester) with a dead weight of 500 grams. The machine counts the number of double folds necessary to rupture the paper. The results, appearing in Table IV, are the means and standard deviation of six trials at the 90% level of confidence.
Table IV Folding Endurance Test Resultsa
3.1.5 Tensile Strength12
Tensile strength of all paper samples was obtained on an Instron Model TM-M 1101 Universal Tester. The data were recorded as stress versus time under a uniform increase in extension, and are reported as breaking strength in kilograms. The results appearing in Table V are the means and standard deviations of three to six trials at the 90% level of confidence.
Table V Tensile Strength Test Resultsa
3.1.6 Surface pH12
Surface pH was measured on all paper samples, using a Beckman Expandomatic SS-2 pH meter with an Ingold glass electrode. The pH meter was calibrated with buffer solutions of pH 5.0 and 7.0. Distilled water was dropped from a medicine dropper onto the paper surfaces at the reading sites. The electrode was rinsed with distilled water and wiped dry with Kimwipes between each reading. Nitrogen gas was bubbled through the distilled water to maintain the pH of the water at 8.3–8.6. Three readings were taken on each paper. Results appear in Table VI and are the means and standard deviations of 18 readings on 6 papers at the 90% level of confidence.
Table VI pH Test Results
3.1.7 Visual Examination
All paper samples were examined under illumination from a Macbeth Spectralight light box set at maximum brightness of the daylight setting. The surfaces of the papers were examined to note any alteration in texture.
A minimum of three paper samples with the same treatment and aging were viewed under ultra-violet illumination from the Macbeth Spectralight light box. Samples from sets of untreated papers, aged and unaged, were compared with the treated samples to separate changes in fluorescence due to aging from those due to treatment.
Preaged and unaged papers which received the same eraser treatment could not be differentiated in the photomicrographs. The set of photomicrographs taken at a higher magnification and using transmitted light showed very clearly that attempts at complete removal of eraser crumbs were unsuccessful. All of the eraser treatments employed left eraser crumbs among the paper fibers.
The set of photomicrographs taken at a lower magnification and using raking light was moderately successful in recording observed surface abrasion caused by certain eraser treatments. The surfaces of papers treated with the Pink Pearl and Kneaded Rubber erasers are abraded; a lifting of individual fibers above the plane of the paper was clearly evident. No such disturbance was recorded on the surfaces of papers treated with either the Magic Rub eraser or the Opaline Pad. The small depth of field of optical microscopy limits it as a technique for recording surface abrasion of paper. Plans have been made to subject eraser treated samples to scanning electron microscopy in order to improve the documentation of effects of eraser treatments and of brushing on the paper surface.
3.2.2 Fold Strength
Untreated, unaged Whatman paper had a fold strength of 59 ± 4 double folds to rupture which fell to 34 ± 10 after 16 days of dry oven aging. Little or no reduction in fold strength is observable as a result of eraser treatments. The effect of pre-aging, post-aging, or brushing the samples was not detectable when comparison is made with untreated samples.
3.2.3 Tensile Strength
Untreated, unaged Whatman paper had a tensile strength of 4.3 ± .1 kg. which was virtually unchanged after 16 days of dry oven aging. As with the folding endurance tests, no reduction in strength was observed as a result of eraser treatments.
3.2.4 Surface pH
The surface pH of untreated, unaged Whatman paper was 7.4 ± .1 which was virtually unchanged after 16 days of dry oven aging. Samples treated with the Kneaded Rubber and Magic Rub erasers, whether or not brushed to remove surface crumbs, retained that pH within .2 pH unit upon aging. Papers treated with the Opaline Pad and Pink Pearl eraser increased in pH by about 1.0 ± .2 pH units. No effect of aging or brushing was detectable. A spot check on the unerased sides of papers treated with these two erasers showed pH values lower than the erased sides but slightly higher than untreated papers.
Since both aged and unaged Art Gum erasers, chemically identical to Opaline crumbs, had an acid pH, the magnesium silicate in the Opaline Pad (see Table I) was indicated as the alkaline agent. Magnesium silicate deposited on an unaged Whatman paper sample increased the paper's pH from 7.2 to 8.2, an effect consistent with that observed on Opaline treated paper sample, suggesting that the magnesium silicate is the alkaline agent.
The procedure for measuring the surface pH involved dropping distilled water on to the surface of the paper. It was noted that certain treated papers exhibited a resistance to wetting. The papers exhibiting the most resistance to wetting were those treated with the Pink Pearl eraser. Papers erased with the Kneaded Rubber eraser were resistant to wetting after post-aging and pre- and post-aging. The Opaline Pad caused a slightly less dramatic effect, though upon wetting, papers both pre- and post-aged with no attempt to remove crumbs had a spotty appearance. Only the Magic Rub eraser caused no incidence of altered wettability. After 16 days of aging, only the papers treated with the Kneaded Rubber eraser continued to resist wetting.
No color change was detected between unaged and aged, untreated samples. Color changes did occur in treated samples, and these generally increased with post-treatment aging time. The color changes, which were too subtle to be documented by Munsell color chips, may be attributable to: 1) a loss of brightness resulting from the disturbance of the erased surface, and 2) deposition of eraser material on the surface and within the fibers of the paper. The erasers are discussed in the order of decreasing color change on the treated papers. The papers erased with the Pink Pearl eraser lost their brightness immediately. With increased aging, papers with no brushing appeared warmer and brushed papers appeared grayer and dirtier. To a lesser extent than Pink Pearl, the Kneaded Rubber eraser resulted in a dirty appearance on all papers tested, which increased with longer aging. All papers treated with the Opaline Pad became increasingly warmer in appearance with aging. Papers treated with the Magic Rub eraser were unchanged except for pre- and post-aged and 16 days aged papers with no brushing for crumb removal. The pre- and post-aged papers were slightly warmer and grayer than unaged, untreated papers. The 16 days aged papers were even grayer.
It was expected that there would be a correspondence between the fluorescence of an eraser and of the papers treated with that eraser. However, no significant differences in fluorescence as a result of eraser treatments were found. The intensity of fluorescence depended upon the aging time of the paper, with all unaged papers fluorescing the least. Previous experimenters found that paper decreases in fluorescence after being heated at 105°C for one hour.13
3.2.8 Surface Abrasion
One week of pre-aging had no influence on the susceptibility of papers to abrasion by erasers. Papers erased with the Pink Pearl eraser showed the most dramatic abrasion in that the surface fibers of the Whatman paper were lifted up from the plane of the paper. The Pink Pearl crumbs adhered most tenaciously and required more brush strokes for removal from the paper than the other erasers.
The Kneaded Rubber eraser also caused abrasion in the treatment. It seemed to pull on the fibers as it was pulled across the paper surface. Very few crumbs were visible from the Kneaded Rubber eraser, and the least number of brush strokes was required to remove visible crumbs.
Papers erased with the Magic Rub eraser exhibited a small amount of abrasion, particularly along the edges of the papers. Fewer brush strokes than were used with the Pink Pearl were necessary to remove visible Magic Rub crumbs.
The Opaline Pad was the least abrasive cleaner, such that no change in the texture of the paper was visible to the naked eye. The greatest amount of brushing was necessary to remove visible crumbs.
There are some interesting parallels between the results of McInnis' study and the current study. McInnis used many materials in common with this experiment: Whatman Chromatography #1 paper, Kneaded Rubber and Art Gum erasers, a dry cleaning pad identical to Opaline, and a white Mars Plastic synthetic eraser, which, like Magic Rub, is a vinyl. Preaging conditions were identical; eraser treatments were gentler: four strokes compared with ten performed in this work. The crumbs from the dry cleaning pad were manipulated with a brush and not with the pad itself as in this study. In McInnis's report, examination of treated papers was exclusively optical, but a scanning electron microscope was employed. The parallels in the findings are as follows: 1) preaged and unaged papers respond identically to eraser abrasion; 2) the Kneaded Rubber eraser was particularly damaging to paper fibers; 3) the dry cleaning pad was unabrasive; 4) the Mars Plastic eraser could be used without abrasion; 5) all of the erasers leave particulate matter among the paper fibers.
The earlier McCrone findings are more well known, since they are abstracted in Carolyn Horton's Cleaning and Preserving Bindings and Related Materials, and the text of this book recommends materials based on McCrone's work.14 The Opaline Pad, Pink Pearl, and Magic Rub erasers were included in this report, and treatments were applied to both rag and wood pulp paper samples. Aging was 100 ± 1°C for 27 days in a circulating air oven. Tests performed were microscopic examination for fiber damage, cold extraction pH, and fold and tensile strength.
No change in fold or tensile strengths or pH's was found; and there was no fiber damage observed though there is no description of how the erasers were used. The report states that Pink Pearl and Magic Rub erasers, which contain CaCO3, are “ideal abrasives for book materials, especially if they remain in the book material” due to their alkalinity.1 The report says that the effect of CaCO3 on the cold extraction pH performed was invisible because CaCO3 is not water soluble.1 However, in discussing dry cleaners used on vellum in another section of the same report, the Pink Pearl and Art Gum erasers are recommended over the Magic Rub eraser because the pH of the vellum treated with Magic Rub was .1 of a pH unit lower than vellum treated with the other two erasers.1
The difference between McCrone's uniform cold extraction pH findings for all of his aged, treated papers and the variation in pH obtained in the current study may be due to the great dilution of eraser residue in McCrone's cold extraction solution. How much eraser material was deposited on McCrone's paper samples is not stated. Cold extraction and surface pH measurements often produce different values.15
Among the questions generated by the current study is whether a more effective means for eraser crumb removal can be developed. A consequence of eraser particulate in paper may be that solvents used for tape and mount removal may swell eraser particulate while it is enmeshed in the paper fibers. Art Gum, Opaline, and Pink Pearl erasers, soluble in warmed acetone-hexane mixtures, may swell in either solvent used alone. Brushing is clearly not effective for removal of the particulate material, and it may even enmesh the particulate deeper into the paper fibers.
A potential major drawback of the Magic Rub eraser which requires further investigation is the thermal degradation of its constituent plasticized poly(vinyl chloride). The eraser immediately became soft at 100°C, and Paul Banks noted the dissolution of the yellow paint on pencils stored in a drawer in direct contact with a vinyl eraser.3 Dioctyl phthalate is a paint solvent. At 370°C heating for 30 minutes, plasticized poly(vinyl chloride) may be more hazardous than the scope of our tests has shown.
It should be noted here that erasers have been used in the conservation of materials other than paper, such as in the cleaning of stone statuary or of metallic threads, and in the use of absorbent crumbs to remove surface dirt from a variety of media. The results of the study conducted here cannot be generalized to evaluate erasers for these other uses, but these results demonstrate the necessity for evaluating these products in all of their conservation applications.
- All products tested using several dry cleaning procedures altered surface characteristics but not mechanical properties of Whatman Chromatography paper.
- All the erasers tested showed marked alterations upon dry oven aging. Dimension change was greatest for the Pink Pearl eraser, and least for the Magic Rub eraser. Weight change was greatest for the Art Gum eraser, and least for the Magic Rub eraser. The surface pH of the aged erasers changed by about one unit except for the Art Gum eraser, which exhibited negligible surface pH change upon aging. All erasers exhibited color change, and became more odorous.
- The eraser treatments regardless of aging or brushing produced no measurable alterations on the folding endurance or tensile strength of the paper. The Opaline Pad and Pink Pearl eraser treatments caused increases in the surface pH of the paper; treatment with the Magic Rub and Kneaded Rubber erasers left the surface pH unaffected. Subtle color changes were detectable as a result of treatment with each of the erasers. The wettability of the paper was decreased by all eraser treatments except those using the Magic Rub eraser.
- Treatments using all eraser samples left detectable amounts of eraser material in the paper. Photomicrographs showed that attempts at complete removal of eraser crumbs by brushing were unsuccessful.
- The Magic Rub eraser was the least altering to the paper, and the eraser itself was the most stable to aging. Papers treated with the Magic Rub eraser suffered negligible abrasion and color change, and had no change in either surface pH or wetting ability.
- The Opaline Pad was even less abrasive to treated paper samples than the Magic Rub eraser. Slight warming of the color of the paper surface after treatment and aging was noted and is probably due to the color change in the eraser crumbs. The surface pH of the paper increased after treatment.
- The Kneaded Rubber eraser was judged abrasive as used. It adversely decreased the wettability of the paper after treatment. The eraser changed dimension upon aging. The crumbs were particularly difficult to remove, as they were small, not visible to the naked eye, and clung to the paper fibers.
- The Pink Pearl eraser was judged the worst eraser because it readily abraded the paper surface and required working over the paper excessively to remove visible crumbs. The abrasion and pink particulate matter altered surface color and texture of the paper. Paper wettability decreased after treatment.
Walter C.McCrone Associates, “The Report on Testing Book Cleaning Materials,” Report to the Library Technology Project No. 50, July, 1966, unpublished mss.
Walter C.McCrone Associates, Appendix 4 in Horton, Carolyn, Cleaning and Preserving Bindings and Related Materials, 2nd Ed., American Library Association, Chicago, 1969, p. 64.
Banks, Paul, “Paper Cleaning,” Restaurator I, 1969, pp. 52–53.
McInnis, Kerry, “Two Studies in Paper Conservation Practice,” I.C.C.M. Bulletin, 6, June, 1980.
ElizabethMoffatt, Conservation Scientist, Canadian Conservation Institute, has also been conducting research on the composition and behavior of eraser products used in paper conservation (private communication, September, 1981).
Munsell Color Company, Munsell Book of Color, Baltimore, Md., 1929–1970.
Mr.WalterIsrael, Chemist at Durasol Drug and Chemical Company, reports that two of the other dry cleaning pads manufactured by Durasol Drug and Chemical Company but distributed by other companies are Draft Clean Pads by Archival Aids, and ABC Draftsman's Dry Clean Pad by Keuffel and Esser Co. (private communication, Fall, 1980).
Paper Chromatography Laboratory Guide, Bulletin No. 201, 1977, Whatman, Inc., Clifton, N.J., p. 14. Whatman Chromatography #1 lacks uniform aging characteristics from roll to roll. Nelson, J.R. “Effects of Wash Water Quality on the Physical Properties of Three Papers,” Publication of the Art Conservation Training Programs Conference, N.Y., 1981.
This was determined according to ASTM methods, described in Paper and Paperboard: Characteristics, Nomenclature, and the Significance of Tests, 1963, as follows: The paper strip was dampened, allowed to dry, and then observed under low magnification. The wire pattern became evident.
Köhler Illumination is used for high resolution, and is described in McCrone, W., McCrone, L., Delly, J., Polarized Light Microscopy, Ann Arbor Science, Michigan, 1979, pp. 30, 32. The intensity on the rheostat was adjusted such that the camera's meter was balanced when the shutter speed was 1/4 second.
The film for both sets of slides was Kodak Ektachrome Tungsten, ASA 160.
Procedures for folding endurance, tensile strength, surface pH, etc. have been described previously. N. S.Baer, N.Indictor, W. H.Phelan, “An Evaluation of Adhesives for Use in Paper Conservation,” Guild of Book Workers Journal X, No. 1, 1971, pp. 17–35; N.S.Baer, N.Indictor, T.I.Schwartzman, I.L.Rosenberg, “Chemical and Physical Properties of Poly (vinyl acetate) Copolymer Emulsions,” ICOM Paper, Venice, Italy, 75/22/5, 1975, Paris.
Radley, J.A., and Grant, J., Fluorescence Analysis in Ultra-Violet Light, Chapman and Hall, London, 1954, p. 455.
Horton, Carolyn, Cleaning and Preserving Bindings and Related Materials, 2nd ed., American Library Association, Chicago, 1969, pp. 32–34.
A.Joel, N.Indictor, J.F.Hanlan and N.S.Baer, “The Measurement and Significance of pH in Paper Conservation,” IIC-AG Bulletin12 (2), 1972, pp. 119–125
Paciorek, K.L., Kratzer, R.H., Kaufman, J., Nakahara, J., Hartstein, A.M., “Oxidative Thermal Decomposition of Poly (vinyl chloride) Compositions,” The Journal of Applied Polymer Science18, 1974, pp. 3723–3729.
I WOULD LIKE to gratefully acknowledge Professors Norbert Baer and Lawrence Majewski of the Conservation Center at New York University for their support of this project. Warm thanks are extended to the members of the paper research class for their feedback and advice. I am also extremely grateful to James Frantz of Objects Conservation, Metropolitan Museum of Art, for use of the Infra-Red Spectrophotometer.