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Conserving the Mason-Dixon Map

Mason-Dixon Map Cartouche by Pamela Young

Among the seventy-three rare and antique maps and atlases in the "Degrees of Latitude" previously exhibited at Colonial Williamsburg's Dewitt Wallace Museum hung "A PLAN of the West Line or Parallel of Latitude which is the Boundary between the Province of Maryland and Pensylvania." The misspelling of Pennsylvania is as authentic as the hand-drawn, manuscript original of what we know as the survey of the Mason-Dixon Line. Executed in the eighteenth century to settle a seventeenth-century border dispute, it came in the nineteenth to demarcate the cultural limits of North and South. From a cartographic point of view, perhaps, it did no more than delineate, precisely, east to west, a reach of the fortieth parallel, taking into account for the first time the roundness of the planet-which, at the time, was quite a lot.

The fortieth parallel was the upper boundary of a large land tract Charles I granted in 1632 to Cecilius Calvert. We know much of it as Maryland. Charles II used that border, too, in 1681 when he gave William Penn a larger tract north of Calvert's that we know as Pennsylvania. But Penn drew the dividing line farther south than Calvert, starting an argument that overlapped not only borderlands but generations of their families.

Penn encouraged settlement on a swath of territory the Calverts claimed, and told property owners to pay taxes to Pennsylvania. The Calverts told the settlers to pay Maryland. The settlers paid neither. Sheriffs arrived to enforce the laws of each colony, and there was bloodshed.

In 1750, an English court approved a compromise settlement of the dispute, but it put Pennsylvania's lower border fifteen miles south of Philadelphia, below the fortieth latitude. Provincial boundary commissioners asked the Royal Observatory in England to recommend surveyors to fix that, and were referred to astronomer-mathematicians Charles Mason and Jeremiah Dixon.

Mason and Dixon started in November 1763, calibrating position and direction by the heavens, measuring the ground with rods and chains, and keeping meticulous minute books. They hired guides from the Iroquois and Six Nations to lead them through the wilderness, and for guards and axe men.

Late in 1767, the party, thirty-six miles shy of the end of its trek, reached a warpath the Six Nations used to attack the Cherokee. The guides would go no farther. Not until four years and nine months after they began were the line's last lengths drawn.

The map charts an area two hundred thirty-three miles long and six miles wide, documenting rivers and creeks, mountains and ridges, forests and dwellings. It is a landmark in the history of geodesy-the science of the size and shape of the earth. Until then, geodesy largely had been theoretical; it had not been applied to boundaries long enough to be complicated by the earth's curvature. Their survey became a model.

Now in private hands, the Mason-Dixon map came to the paper conservation lab in Colonial Williamsburg's Dewitt Wallace Collections and Conservation Building for treatment before display. Treatment begins with examination to define condition and the maker's materials and technique.

The map is six and three-quarter inches by seventy-six and three-quarter inches. It spans six sheets of rag paper, lap-joined and lined with finely woven linen. The cloth supported a document intended to be unrolled and rolled repeatedly. Image and text are rendered with pen and brush in black ink over a preliminary pencil drawing. Green paint, perhaps representing the verdant terrain, was irregularly printed. Below a cartouche at the far right, the panel is signed, in brown ink, "Cha. Mason Jere: Dixon."

Conservator Pam Young uses a surgical scalpel to separate the map from its linen lining and remove as much as possible of the adhesive originally used to attach the map to its backing.
Conservator Pam Young used a surgical scalpel to separate the map from its linen lining and remove as much as possible of the adhesive originally used to attach the map to its backing.

There were stains and discolorations; surface soil; buckling; large, hard-fold creases and fractures; edge tears; and abrasions. Apparently, the map had been rolled to languish in storage exposed to insects. In the first leaf, near the lower edge, there were irregularly shaped losses suggesting silverfish damage and exposing the fabric lining. Symptoms of insect infestation included speck-like brown accretions and tiny, circular, brown stains.

Soon after the drawing was completed and the survey approved, the map was sectioned for transfer to copperplates for engraving and printing. The sections were re-joined with linen strips, and edges of the joins were lifting. Oxidation of the green paint, a verdigris pigment, turned it brownish. Ultra violet light, or sulfurous environmental compounds, may have caused that.

The paper was lined before paint and ink applications. The lining's weave left an impression, and the manner in which the paint was laid on corresponds to irregularities in the paper plane caused by lining's texture. Microscope analysis revealed that the black ink is beneath the paint throughout most of the map, but over it in the capital lettering of the legends.

We had to know how the map would react to conservation. We tested the graphite pencil, carbon-based ink, and verdigris paint for water solubility, and they proved stable in the presence of moisture. But the signatures were written in iron-gall ink, soluble and prone to feathering or bleeding. That determined the limit of the treatment.

The paper was stable, but the fabric lining and its flour paste created stress. Small pockets of delamination between paper and lining were visible. Did the map's condition warrant deconstruction and removal of original elements? Untreated, would the map suffer further?

Treatment was chosen.

Given the age and use of the map as a working document, it was in very good condition. The linen lining allowed the paper to be rolled, unrolled, and handled with relatively little damage. Though the lining was original and historically important, distortions associated with its attachment were damaging. Abrasion, and torn and lifting segments covered the apex of wrinkles and creases. Because the map no longer has to function, removal and replacement were elected.

The first step of treatment was reducing with eraser crumbs paper surface soil-particulates, and, probably human skin oil deposited during handling. Like insect specks, they are acidic and harm fibers. The erasures prevented soil from sinking further in during aqueous treatments, removed most of a black particulate layer along the left edge, and lifted generalized soil, reducing acidity and improving the image. Undertaken primarily within margins, it did not touch pencil drawings.

After the original backing was removed, Young attached one made of Japanese paper to the map faced down on the table.
After the original backing was removed, Young attached one made of Japanese paper to the map faced down on the table.

The adhesive was a flour paste, typical of the period and situation. It was available, inexpensive, and easily mixed. To soften and swell the paste, de-ionized water was brushed on the lining backing, penetrating the fabric, and softening the adhesive. Gently, we scraped the lining with a scalpel, loosening its attachment, and, millimeters at a time, pulled it away. The adhesive was brittle, discolored and impure. While the paste was soft, the bulk was scraped carefully from the paper. More was removed by rolling water-dampened swabs over small areas. So it went for more than 200 hours over seventy-six inches.

In conservation jargon, "fixing" means applying a compound to temporarily isolate an artifact's vulnerable elements to allow more thorough work. Subsequent bathing and lining required the use of more water, but the signatures were very sensitive to moisture. The fixative chosen was cyclododecane, a wax-like solid soluble in non-polar, aromatic solvents, but insoluble in water. A saturated solution was prepared in toluene and applied with a fine hair brush. The solvent carried cyclododecane over the inked signatures and into the surrounding paper. As the solvent evaporated, the waxy solid remained, protecting the signatures from moisture. Exposed to air, the cyclododecane disappears, changing from a solid directly to a gas. No residue is left, and the signatures remain as they were.

Working millimeter by millimeter on a light box, Young applied pieces of Japanese paper, made from flax and mulberry and attached with wheat paste, to mend tears and breaks in the map. She used bits of colored paper pulp to fill in the holes.
Working millimeter by millimeter on a light box, Young applied pieces of Japanese paper, made from flax and mulberry and attached with wheat paste, to mend tears and breaks in the map. She used bits of colored paper pulp to fill in the holes.

It was important to remove flour paste imbedded in the paper fibers because paste shrinks and hardens when dry. Any vestige would make the paper pucker. We selected an enzyme-a protein molecule that speeds chemical reactions-to digest and remove it. We mixed Alpha-amylase into solution to digest the starch, and applied the enzyme protease to digest the paste's protein into molecules soluble in water, and easily removed with moisture. Most of the map was floated in a tray of the enzyme solution, and rinsed in de-ionized water.

We bathed the map with a dilute calcium solution to reduce stains, discoloration, and acidity, put it on absorbent blotter paper, and laid it on a tablet that has a perforated panel attached to a suction pump. The pump creates a vacuum that pulls the map and blotter into close contact while air moves through the paper. Water sprayed over the map moves quickly through, rinsing stains and discoloration into the blotter.

Tears were mended and breaks reinforced with thin strips of lightweight Japanese paper made of flax and mulberry. Its long fibers reinforce the map paper, but are almost invisible when adhered with wheat paste. Paper pulp was toned with acrylic paints to fill losses, and to make the insect damage inconspicuous.

To simulate the purpose of the original lining, and restore the arrangement of the joined section, we selected a heavy weight Japanese paper. The three sections were lined and dried between blotters. Each section was aligned and joined with heavyweight strips of Japanese paper and wheat paste.

After conservation, digital copies were made of the map.
After conservation, digital copies were made of the map.

With a fine hair brush, and watercolors we in-painted losses to the outline, and, treatment complete, we hinged the map to a mat and framed it. The result was on view at the DeWitt through March 2006 in the exhibit, "Degrees of Latitude."


Pam Young, a Colonial Williamsburg conservator, contributed to the winter 2001–2002 journal, "The Tale of the Red-winged Blackbird."

This article originally appeared in The Colonial Williamsburg Journal, Volume 28, Number 1: Winter 2006.