Understanding Paper: Structures, Watermarks, and a Conservator’s Passion

By Leonie Müller
May 7, 2021
A woman with long hair and glasses is leaning over a light table in a laboratory to examine a sheet of paper.
Paper conservation fellow Leonie Müller looks at an artwork on paper in transmitted light.

There is more to paper than meets the eye. Paper conservation fellow Leonie Müller shares with Index readers the material qualities of paper and how its structures reveal the process of how it’s made.

As a paper conservator, I am fascinated by the structure of paper and how different it can look, feel, and even sound—it can be rough or smooth, glossy or matte; it can have varying shades of white or be colorful; and it can sometimes rustle when carefully handled. These are properties that paper conservators try to describe when looking closely at a work of art on paper, and I invite you to take a closer look with me.

Structures and Process

In Penley Knipe’s article about blue paper making, we learned how paper has traditionally been made. But we can also learn about production processes from paper itself. The properties I described above are the ones we see under normal light, which conservators call visible light. In the Straus Center, we like to use light bulbs that resemble daylight, so the color we perceive is the most natural. But when we tip the lamps at our workbenches a bit or use a handheld flashlight, we create what’s called raking light. In this light, color is not what we are looking for. Suddenly, tiny shadows appear, cast by the uneven surface of the web of cellulose fibers that form the sheet. Also detected are slight indentations from the manufacturing process. For example, raking light can reveal the texture created when felts are pressed against a wet sheet of paper. Raking light lets us perceive paper in three dimensions.

This photograph shows a piece of paper very close up, with a soft, uneven texture and regular vertical lines, suggesting indentations. It is resting on a gray surface. Below the paper to the right is a thick black line marking one inch.

Shown in raking light, the uneven surface of a laid paper becomes visible. This piece of paper shows where the mould made indentations.
This photograph shows a piece of paper very close up, with a soft, uneven texture and regular vertical lines, suggesting protrusions. Below the paper to the right is a thick black line marking one inch.

In raking light, you can see where the felt was pressed against the same paper on the other side.

In Europe, paper was originally made on moulds, which are wooden frames with a tight web of wires supported by wooden struts. A “vatman” would dunk the moulds in a vat filled with pulp and lift them up again, slightly agitating the pulp collecting on the mould while doing so to form an even sheet. He then would pass the mould on to the so-called coucher, who would press the now-formed paper sheet onto a piece of felt.

Asian paper is made using a flexible mat of bamboo splints sewn together and positioned on a wooden frame for support, which is also dunked in a vat. The mould is submerged several times and shaken in a rigorous back and forth movement in between dunks. The paper sheets are then pressed on top of each other by the vatman, who removes the bamboo mat from the frame and rolls it over a surface to release the paper from the mat.

In both traditions, the laid structure in the paper forms because the fibers from the pulp that collect on the mould sink into the small spaces between the wire or bamboo, leaving fewer fibers on the protruding parts of the mould. This makes the paper a bit thinner in these elevated areas. Sometimes the pattern is more pronounced, but other times you need to know what to look for: a grid of strong vertical lines, called chain lines, divided by more delicate and plentiful horizontal lines, called laid lines. We call this kind of paper laid. When we change the angle of light and let the light shine through the paper, we create transmitted light—that’s when the chain and laid lines become clearly visible.

In 18th-century Europe, the idea of covering the mould with a tight metal mesh, which keeps the pulp from sinking between the wires, resulted in the invention of a paper with a smooth surface, free of chain or laid lines. Because of its even structure, this paper is called wove paper.

Of course, not all papers exhibiting a laid structure are handmade. Industrial paper making began in the late 18th century, and with the invention of the cylinder mould machine—a cylinder covered with a mould that picks up pulp in a continuous movement—it became possible to produce laid papers on a larger scale. These machines are still used today to produce high-quality papers.

A smooth reddish-brown sheet of paper illuminated from the back. A thick black line marks one inch at bottom left.

In this wove paper, seen in transmitted light, the surface appears homogenous.
A piece of brown paper shows thin parallel horizontal lines and six vertical lines. In the top third of the paper, the horizontal lines are irregular. A thick black line marks one inch at bottom left.

By contrast, in transmitted light this laid paper shows a clear pattern. You can see that the paper mould was mechanically damaged, as the chain line structure near the right edge is irregular. This feature would be visible in all sheets made from this mould.

Watermarks

Like chain and laid lines, watermarks become clearly visible in transmitted light because they are thinner areas that show as bright lines. They are made by sewing a bent wire to the top of the mould, causing fewer fibers to form the sheet in the protruding areas. This explains why watermarks are not found on older Asian papers, as the flexible bamboo mould does not allow for wire or other attachments.

  • A light brown sheet of paper has a fine grid of lighter, parallel lines. Slightly off-center to the left is a watermark of a standing eagle with flapping wings, circumscribed by a circle that holds up a crown. A thick black line marks one inch at bottom left.
    of This European paper shows a watermark of an eagle.
  • A light brown sheet of paper appears structured by a fine grid of lighter lines with slightly irregular distances in the vertical lines. A thick black line marks one inch at bottom left.
    of This Asian paper has closely spaced chain (vertical) lines, including a more narrowly spaced pair in the left half of the sheet. Because of the flexible construction of the mould, no shadows from the supporting frame are visible.
  • A light brown paper with a regular grid pattern features a watermark with fanciful letters and, above the lettering, a side view of a winged bird. A thick black line marks one inch at bottom left.
    of This thin handmade paper has a laid structure and an inscription-style watermark. The shadows around the chain lines were caused by the wooden support bars in the mould.
  • A dark red paper is structured by a regular grid pattern. Close to its right edge, watermark letters spell out “Ingres-Fabriano.” A thick black line marks one inch at bottom left.
    of This thick machine-made paper has a laid structure and a watermark.

The oldest known watermarks date to 13th-century Europe and were considered marks of origin, though sometimes they indicated quality levels. They often featured a symbol or, later, initials, representing the paper mill or paper maker—an early form of a trademark or brand logo. They could also be customized to bear a royal symbol or the coat of arms of a particular city. Watermarks evolved continually, from reflecting the personal preferences of a papermaker to conforming to official guidelines on how a paper mill would need to mark its papers under penalty of law. Because watermarks and their use changed over the centuries, there is much room for interpretation. They have cultural, historical, and of course, artistic value and continue to inspire historiographic research.

A brown sheet of paper exhibits a regular grid pattern and, in its center, a shield with a capital letter M from which a star rises. A thick black line marks one inch at bottom left.
This antique laid paper with a watermark was presumably made in the 16th century in Italy. The watermark sits between broader spaced chain lines and is supported by an additional thinner wire, which was a customary practice in Italy.

By researching watermarks and closely inspecting irregularities in chain and laid lines in paper, we can make assumptions about where and when paper might have originated. This in turn can help authenticate historical documents and works of art. Because industrialization of paper making is a relatively new technology, the paper used for printed objects, both books and prints, normally shows consistency. Paper was bought in reams and was most likely used right away rather than stored, since the material was considered valuable. The prestige (and price) of high-quality paper even led some producers to forge watermarks and claim the fame of other paper mills!

Besides the mould-made structures in the paper, there are other traces of manufacture we can see. The evenness of the fiber distribution indicates the quality of both the paper and the pulp used. A cloudy paper with irregular thickness, for example, tells us that the pulp was not beaten thoroughly enough and knots of fibers floated in the vat, or the fibers could not be distributed evenly. This kind of lower quality paper may have been cheaper to buy and was possibly used for packaging and other everyday applications, such as drafting paper in offices.

A brown sheet of paper is structured with a regular grid. Toward its right edge multiple lighter spots form an irregular pattern. A thick black line marks one inch at bottom left.

This sheet shows an uneven thickness and a frizzy structure along the lower edge, which might have been caused by agitating the pulp slurry on the mould too vigorously.
An almost black sheet of paper reveals several randomly placed lighter spots. A thick gray line marks one inch at bottom left.

This toned paper shows an uneven thickness.

Some papers clearly show traces of the production process, both deliberate and accidental. Long, strongly colored fibers that are visible without magnification can often be identified as wool. Wool was used to give paper a specific tonality and texture, making it more voluminous and rougher on the surface. Artists working in dry media, such as pastels, appreciate this surface quality. Or consider the little circles in sheets of paper called “vatman’s tears.” These are the result of water dripping on the newly formed sheet while it is still wet. At this stage of the process, paper is very vulnerable. Full sheets can have a pulled edge, which is an effect that occurs when the papermaker’s assistant stretched the still-malleable paper while removing it from the felt.

A dark brown sheet with a regular grid pattern in lighter lines features a partially visible lion in the upper half and, in the lower half, several larger lighter spots in random places. A thick black line marks one inch at bottom left.
This paper with a fragmented watermark shows several “vatman’s tears.”

In the past, moist sheets were dried on ropes or thin wooden rods, which shows up as wrinkles, usually along the center of a full sheet. The uncut edges of a full sheet give a good indication of how the paper was produced. Compare, in the images below, the wavy, deckled edge on all four sides of handmade paper with the watercut edge found in paper made by a cylinder mould machine. To make watercut paper, the pulp of the formed sheet on the conveyor belt is incised with water, which creates a weak spot where the paper can easily be torn apart in the production process. These clearly visible differences help us guess the age of the paper, since they align with developments in paper making history.

  • A gray sheet of paper has several straight lines that appear to be indentations and protrusions. A horizontal indentation runs across around the middle of the sheet. The left edge of the sheet appears wrinkled. A thick black line marks one inch at bottom right.
    of This paper seen in raking light shows the felt side as well as rope-induced wrinkles from the drying process at left.
  • A light brown sheet with a regular grid pattern shows a more irregular edge, with areas of various thickness and multiple inclusions. A bird watermark is at lower left, and a thick black line marks one inch at bottom right.
    of This image of a handmade paper shows the deckled edge on the top and right side of the sheet.
  • An even-colored dark orange sheet has a lighter colored edge on the right side. A thick black line marks one inch at bottom left.
    of Note the watercut edge of this paper produced on a cylinder mould machine.

All these features capture my attention when I look at a sheet of paper, and even though we try to take photos to document memorable paper structures, most of them are well hidden to the casual observer. But they tell us a lot about the origins of this important artist’s material that’s often taken for granted. When you see a work on paper in the future, I hope that you will not only appreciate the artistic image that sits on top, but also value the information embedded in the paper itself. You might enjoy deciphering it as much as I do!

 

Leonie Müller is the Craigen W. Bowen Paper Conservation Fellow in the Straus Center for Conservation and Technical Studies at the Harvard Art Museums.