Sample Preparation

Some of the methods we wanted to use were destructive, requiring samples be taken of the object to be studied. To find study subjects for which this could be done, we turned to the Barrow Book Collection, which is held at the Library of Congress. William J. Barrow (1904-1967) conducted a series of scientific studies on the degradation of paper at the Virginia Historical Society between in 1963 and 1965. His study collection, which contains about 1000 books printed produced between 1507 and 1899, is part of the Center for the Library’s Analytical Science Samples (CLASS) collection in the Library’s Preservation Research and Testing Division.

Opera Omnia, Amsterdam, 1661

Paper in old books, maps and other documents, and artworks can vary significantly. It can contain fiber from cotton, flax (linen), hemp, jute, or other plants. Fiber length will vary depending on the pulping process. The water used to produce it may contain soluble impurities such as acids, or insoluble ones such as silt.  It may be sized, to a lesser or greater degree, with one of several substances. 

The Federalist on the new constitution, New York

Model Papers

To limit the number of variables that might affect our results we have created deliberate tidelines on several model papers, selected to represent the historical ones we were examining. One of these is Whatman 1 100% cotton filter paper.


We produce tidelines on this and other papers by suspending them with their bottom edge in a pan of ultrapure water. We than artificially age the samples in an oven to produce accelerated aging equivalent to that which we see in historical samples.


Tidelines form readily on unsized papers and some sized papers. The water creeps upwards from the immersion line by capillary action. When the sample is removed and after it dries, the tideline remains. Aging can make it more apparent. It is easiest to see tidelines with an ultraviolet light.

X-Ray Florescence

X-Ray Fluorescence is a non-destructive analytical technique used to determine the elemental composition of materials. XRF analyzers determine the chemistry of a sample by measuring the secondary X-rays (fluorescence) emitted from a sample when it is excited by a primary X-ray source. 

Synchrotron XRF

At a synchrotron facility such as the Advanced Photon Source (APS) at Argonne National Laboratory, a particle accelerator and storage ring provides ultra-bright, high-energy x-ray beams and the highest resolution for a variety of microscopy and spectroscopy techniques. While a portable XRF device can show us concentrations of elements at the tideline, the high resolution (60 nm) synchrotron XRF at APS Beamline 26-ID can show us how the elements are distributed with respect to the fiber structure itself.

Scanning Electron Microscope

A scanning electron microscope is used to image samples at higher resolution than can be achieved with an optical microscope. The sample surface is scanned with a focused beam of electrons, which interact with atoms in the sample to produce secondary and backscattered electrons and characteristic X-rays that contain information about the sample's surface features and chemical composition. 

Whatman No. 1 – The small holes were made to make the tideline. Note the white particles on the tideline.

X-Ray Computed Microtomography

X-ray computed micro tomography is a high-resolution version of a medical CAT scan system. Images produced by penetrating X-rays are used to reconstruct a three dimensional image of the sample.

High resolution (0.77 micron) image of Whatman No. 1 on sample holder and reconstructed 3D image

A 2 mm square paper sample is centered on a plastic frame and a hole made in the paper to mark the tideline. A series of X-ray images are taken as the object is slowly rotated, and reconstructed into a 3D model. 

Fluorescence Lifetime Imaging Microscopy

Fluorescence Lifetime Imaging Microscopy (FLIM) – produces an image based on the differences in the exponential decay rate of sample fluorescence after excitation by a laser 

Glossary of Terms


Unsized paper is very absorbent, water will spread through the fibers quickly and far. Sizing is a treatment that can be applied when paper is made (internal sizing) or afterward (external sizing). Water doesn’t travel as much in sized papers. Sizing can be gelatin, starch or rosin (Note: alum, alumina sulfate, Al2(SO4)3*18H2O and NaAlO4 are used with rosin). In the western world, sizing was primarily gelatin before the mid 1800s. Starch was used in other parts of the world. ]