What is paper?
Paper is produced by creating a slurry of cellulose pulp in water, then pressing the fibers together into a mat and drying it. Pulp papermaking was developed in Ancient China about two thousand years ago and until the mid 1800s the most common fiber sources were cotton, hemp, or linen rags.
Cellulose is a natural polymer, or long chain molecule, found in plants. The cellulose molecules are organized into elemental fibrils, which 1.5-3.5 nm (or 10-9 m) in diameter. These are bundled into microfibrils, 10-30 nm in diameter, and these in turn form fibers that are around 100 nm in diameter. The mat that we call paper is composed of fibers, fibrils, and finer material ranging in scale from 0.1 nm to 100 μm (10-3 m), and for this reason, we describe paper as a hierarchical material.
This range of size scales in paper means that in order to describe its structure in detail, look for damage to that structure, or characterize the distribution of impurities with respect to the structure, we need microscopy techniques with resolutions ranging from millimeters down to several nanometers.
What are tidelines?
When high-quality 100% cotton paper is partially wetted and then dried, irreversible changes take place at the wet/dry boundary. Impurities in the wetting agent may leave deposits that make tidelines more noticeable. But unlike the tidelines you may see on a beach, tidelines on paper do not simply represent the accumulation of detritus by high water. Scientists have shown that tidelines on paper are signs of irreversible changes in the underlying cellulosic structure.
This work was inspired by a collection of drawings by American artist Louis Comfort Tiffany (1848-1933), who is well known for his breathtaking stained glass windows and mosaics. Behind each Tiffany window is a collection of preparatory works on paper, which demonstrate the enormity of Tiffany’s vision. In 1967, the MMA acquired 420 drawings produced between 1848 and 1930 by Tiffany and his artists. Between 1930 and 1967, this collection had sustained extensive exposure to water, leaving the works with soil, tidelines, delaminated substrates, and fungal and insect damage.
When museums receive objects with damage such as this, they must treat them before they can be displayed. Treatment is time consuming and must be done by trained conservators.
The researchers in this study selected for study several nonaccessioned items from the Metropolitan Museum of Art’s collection that had prominent tidelines, including the botanical print shown here.