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Knowledge Base

Paper Characteristics:

Cold Press, Hot Press, Rough - What's What?

Cold Pressed, commonly referred to as CP (and less commonly referred to as NOT), is a paper surface with a slight texture produced by pressing the finished sheet between cold cylinders.  Mainly a term used for watercolor papers.  Hot Pressed papers are smoother as they are run through hot cylinders at the end of the paper machine. Rough papers are pro­duced by placing wet sheets of paper against textured blankets or air drying (or both).  They produce a grainy effect as water collects in the "valleys" in the paper. It's important to note that there is no standard for the different surfaces.  CP paper produced at one mill may have a vastly different surface than that of another mill.  Your best bet is to try out as many different papers as you can and find what works best for your image.  We have Watercolor Paper Samplers available in our sample department.

What is a Deckled Edge?

The feathery edge of a paper which is the result of the natural run-off of wet pulp when making handmade and mouldmade paper, or the result of sheets being torn while wet.  Machinemade papers can simulate a deckle by cutting the wet paper with a water jet on the paper machine.

What is Dimensional Stability?

The degree to which a paper will maintain its size and shape when subjected to changes in moisture content and relative humidity.  Very important in maintaining registration in printing.

What is Felt finish?

Surface characteristics of paper formed at the wet end of a paper machine, using woven wool or synthetic felts with distinctive patterns to create a texture in the finished sheets.  Also called felt marks.

What is a paper's "Formation"?

The arrangement of fibers in a sheet of paper, which can be seen by holding a sheet of paper to the light source.  The formation is determined by composition of the fibers, fiber length, machine speed and other factors.  
Formation can run from "tight" to "wild" and is a major factor in determining how the sheet will perform, affecting factors like levelness, strength and dimensional stability

What is grain direction?

The direction in which a majority of the fibers lie in a finished sheet of paper.  Grain direction is determined by the fibers' alignment parallel with the movement of the paper as it travels through the paper machine.  (Handmade papers therefore have no grain direction.) Why is this important to you?  Paper folds much more easily "with" the grain direction. One of our favorite blogs has a great section on how to determine grain direction.  Check out what Roz Wound Up had to say.

What are Laid Papers?

Papers with a "grid" pattern in the sheet, resulting from the pulp resting against wires on the papermaking screen.  "Laid" lines are closely spaced while "chain" lines are farther apart and run parallel with the grain direction of the sheet.

What are rice papers?

A common misnomer used to describe Asian papers.  There are no papers actually made from rice - these papers are typically made of Kozo, Mulberry, Gampi or Mitsumata.

Are both sides of paper the same?

All paper has two distinctly different sides. With mould made paper they are called the 'felt' and 'mould' (or 'wire') sides. The 'felt' side relates to the top side of the paper, and gets its name because it touches the natural wool in felt first during manufacture. The 'mould' side in contrast is the side that is in contact with the wire mesh of the cylinder mould that rotates inside the vat of pulp. The 'felt' side is considered superior to the 'mould' side by many artists and printers as it has a more random pattern associated with it, while the wire side is more regular.

What is vellum?

Vellum has a few meanings that tend to confuse. A paper surface is called vellum when it has a fine texture. Vellum is also used to designate heavy weight, translucent drawing or draft­ing papers.

What makes paper acid free?

Paper is considered acid free if its PH level is 7.0.  Paper made from any fiber can be acid free when prepared properly.  Acid free paper is more stable, and will hold its color and rigidity over time.

What is opacity?

Paper's opacity represents the amount that printed material will show on the reverse side.  The more opaque a sheet of paper is, the less printing or dark material will show on adjacent sheets.

What is meant by ply?

A single layer of paper.  This term is often used when several sheets of paper are laminated together to form a board.  This is used in the description of our Drawing Bristol and Rising Museum Board.

What is a plate finish?

Ultra-smooth.  A plate finish is usually used for drawing techniques that require fine detail.

What is a wove finish?

Paper which shows no fine "laid" lines running through its sheets when held to light.  This type of paper will display an even, smooth finish.

What is neutral PH?

pH is a measure of the concentration of hydrogen ions in a solution.  The pH scale runs from 0 to 14 and measures the acidity or alkalinity of a substance.  Seven is pH neutral, numbers below seven represent increasing acidity and numbers above seven indicate increasing alkalinity.  Each step up or down the scale represents a ten-fold change.  Buffered papers typically fall between 8.5 and 9.5 on the pH scale.

Papermaking:

What are cotton Liners?

Linters are fibers that adhere to cottonseed after ginning.  This byproduct of the textile industry is used as the raw material to produce pulp for cotton fiber content papers.  A recovered material, cotton linters would typically otherwise be discarded.

Cotton is the purest form of cellulose produced in nature and it requires the least amount of processing before it can be used for papermarking.

What is mouldmade paper?

Mouldmade papers simulate the handmade process on a mechanised paper machine. These papers can be mistaken for handmade but there are distinct differences.

The mould is not held by the hand; instead it’s replaced by a slowly rotating cylinder mould, which picks up the paper stock from the vat. The paper is then deposited onto a continuously moving woollen felt.

Mould made paper combines the consistent quality of machine made (fourdrinier) papers, but with the individual character of handmade papers. Mouldmade papers are typically much stronger and flexible than a machinemade paper.  

They are of particular interest to artists and printers because of their increased surface strength and beautiful surface texture. Mould made papers won't easily tear because the fibres lay randonly across the sheet, whereas, the fibres in fourdrinier papers tend to lie in one direction, making the sheet weak in this area. 

Depending on the grade of paper, one of the characterists of mould made paper can be gorgeous deckle edges.

What Is Handmade Paper?

To no surprise, this is paper made by hand.  The way this is done is by using a "mould" - basically a frame with is covered with a flat rigit screen (western) or flexible screen (asian).  In both cases, the mould is covered by a flat frame (called a deckle) to contain the run-off of wet pulp, dipped into a vat of wet pulp, shaken to distribute the fibers evenly and drained of its excess water.  

The wet mat of fibers remaining is the newly formed sheet, which is then air dried.

Handmade papermaking can be a totally manual process, involving no electricity.  Handmade papers are one-of-a-kind and have four deckle edges.

There's a great (longer) description here as well.

What Is Sizing?

The process by which a substance (typically gelatin or starch) is added to paper.  Sizing provides resistance to the absorption of moisture and eliminates ink feathering and bleed through.  

In the papermaking process, after the sheet is formed, it may be either "surface sized" - pained or brushed onto the surface - or "tub sized" - immersed in a bath.

What is Kozo?

Kozo is the inner bark of mulberry tree seedlings, producing a naturally white paper fiber which is very strong and long lasting. Kozo is one of the most important fibers in traditional Japanese papermaking.

What's Better About Cotton Papers?

Cotton is widely considered by the global art community the ideal substrate for fine art paper. Cotton fibers are naturally longer than its alternatives like alpha-cellulose (wood pulp) which make for a stronger, more durable sheet. Cotton also makes offers very distinct and luxurious feel, which adds to the overall appeal of the finished work.

Papers manufactured from cotton fiber will last longer and hold up better under repeated handling and various environmental conditions than paper made from wood pulp. 

Not only does paper with cotton content feel good and last longer, but as it's "tree-free", cotton is a natural fiber that is made from renewable and recovered materials.  Cotton linters are identified by government recycling standards as a recovered fiber, boosting cotton paper’s compliancy with most government contracts when combined with post consumer fiber.

What Is "Lignin"?

A component found in the cell walls of plants, lignin is largely responsible for the strength and rigidity of plants, but its presence in paper is believed to contribute to chemical degradation.  Over time as the lignin breaks down it becomes acidic and threatens the longevity of a paper, therefore, it’s important to make sure you work is done on lignin-free paper.

What Is A Watermark?

The translucent design or name easily visible when a sheet is held to the light. A design is sewn onto the paper­making screen with raised wire. When the sheet is formed, the pulp settles in a thinner layer over the wire design.

Here's a great photo of an Arches watermark.  Keep in mind that when the paper is not held to the light, the watermark is very subtle.

What Is Calcium Carbonate?

An alkaline chemical used as a buffering in papers and boards.  It ensures the paper remains acid-free by protecting it against outside pollutants.

What Is Calendering?

The process of pressing paper throuhg rollers to increase its surface smoothness.

What Is Machinemade?

Paper made on a very rapid running machine that can produce consisten quantities of sheets and rolls called a "Fourdrinier".

What Is Alpha Cellulose?

A material used in the paper making process, primarily derived from wood.  During the pulp preparation process the papermaker will remove the lignin's and other impurities from the material.  This is the purist form of wood pulp to be used in papermaking.

Paper Measurements:

What is paper "caliper"?

Caliper is the thickness of a paper measured under specified conditions.  Usually expressed in thousandths of an inch (mils).  One point, or mil, equals 1/1000th of an inch.  Ex. a 15pt sheet is 0.015" thick.

What Is "Gsm"?

Gsm = grams per square meter, or the gram weight of a hypothetical square meter of a particular paper.In our opinion, this is the best comparative measure of a paper because it does not vary with sheets size.

How Do You Convert Paper Weights?

In the metric system, the density of all types of paper and paperboard is expressed in terms of grams per square meter (g/m²). This quantity is commonly called grammage. In countries that use United States paper sizes, a less direct measure known as basis weight is used in addition to or instead of grammage. So how do you tell a 300gsm sheet from an 80lb cover?  You can download our weight converter.  (Password to unprotect the sheet is "legionpaper".)