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Tuesday, August 13, 2013

Article on Paper Making Part 3

Machine versus Handmade

There are essentially three methods of creating paper, two are mechanical and the third is by hand. The two machines you are most likely to hear about are called the Fourdrinier and the cylinder. Occasionally you'll find the cylinder process referred to as mould-made. This is a little confusing for the average watercolorist who would probably assume mould-made to automatically mean handmade.

The Fourdrinier is a high capacity machine with a screen belt, continuously supplied with pulp from a headbox. As the conveyor moves away from the steady stream of spreading pulp, the shaking belt forms the paper, while suction drains the excess water from below. In short order the belt ends, depositing the juvenile paper on another belt to be whisked off for pressing and drying. After being cut into serviceable pieces, it's packaged and sent to your art supplier.

The cylinder machine, which makes mould-made paper, is a bit different ... at least at the beginning of the process. Like a ferris wheel, half submerged in pulp, this horizontal screened cylinder continuously turns, forming a sheet of matted pulp on the screen's exterior. The endless sheet of "formed" paper is deposited on a belt and moved through the drying process with the same haste as in the Fourdrinier procedure. The cylinder machine offers two advantages. First, a thicker sheet of paper can be formed, and second, the grain isn't as pronounced.

Grain, refers to the microscopic alignment of pulp fibers. The Fourdrinier machine, with its speeding belt produces the most obvious grain alignment even though the manufacturer tries to counteract this by shaking the belt as the sheet forms. The cylinder has a slight edge in reducing grain, if it's slowed down. Too much grain can make a visually distracting surface pattern. Grain also causes the paper to expand more in one direction than the other, that can cause problems while painting and framing. Unfortunately this is the price one must pay when using inexpensive, high production, machine-made paper.

Fig 9 20: In a dramatic move, the mould is raised from the vat with excess pulp flying to all sides. This grand gesture is called, "throwing the pulp."

Watching paper made by hand is far more fascinating. The papermaker uses a mould which is a flat sieve of brass wire mesh supported by a mahogany frame with tapered ribs. On top of the wire mesh is another frame. This one, called the deckle, is removable and creates a dam retaining the slushy pulp as the mould is lifted from the vat. The thickness of the deckle frame controls the depth of the pulp layer, and ultimately, the weight, or thickness, of the paper.

To “cast” a sheet, the papermaker dips the mould into the vat of pulp scooping up a load within the retaining walls of the deckle. This is not a delicate move ... it's not meant to be. The excess pulp is removed in a grand motion called "throwing the wave." (See Fig 9 20)

Then the papermaker, holding the frame level, shakes the mould side to side and back and forth until much of the excess water is drained. This action interlocks the cotton fibers and minimizes grain. In papermaking jargon, the sheet is now formed and this is when hydrogen bonding begins. (See Fig. 9 21)