When shopping for art supplies, you might find yourself in Paper aisle (like the one at the Plaza Art in Rockville, Maryland, pictured at the end of this article) and think, Why are there so many different types of paper? Isn't it all just...paper?

There are some big differences in paper quality and if you're a beginning watercolorist or printmaker, it might be a little overwhelming to try and figure out which paper is best for which project. Some paper is quite expensive, and with good reason. This guide will give you a little background on the science and history of paper, so next time you need to buy paper, you'll know what all the labels mean:

What’s the deal with expensive paper?

One of the greatest misconceptions about paper is that all paper is made from trees. Paper can be made from almost any fibrous plant material containing cellulose but fine watercolor, printmaking and drawing papers are almost always made from cotton rag. In fact, paper in Europe was made exclusively from vellum, linen or cotton rags until the mid-1800s.

Why use fine papers?

Fine papers are well worth their cost. Cotton rag is better for professional work because it holds up more reliably over time than paper made from wood pulp. Paper made with cotton rag also maintains integrity under moisture; it does not fall apart when wet. This is why heavy, cotton-based papers are used in many printmaking techniques.

What is the difference between hot press and cold press paper?

The key difference between hot press and cold press is texture. Hot press paper is smooth, whereas cold press paper is textured. Cold press paper has a rougher, heavier tooth—the small bumps and grooves in the paper soak up paint and other mediums more readily than hot press. Hot press has a much smoother and less permeable surface, so pigment rests on top of the surface and appears more vibrant. Because of this smoothness, very watery paint can settle in in “back-runs” and “flowers.” Hot press is better for painting precise, hard lines because it does not absorb water as quickly as cold press; allowing you to re-wet and rework areas more easily.

Hot press papers can be made by pressing the paper between two hot glazing rollers, or by passing it through cold metal rollers under a very high pressure. Hot press is much smoother than cold press.

Cold press paper is made by pressing paper between metal rollers. It is sometimes referred to as “NOT,” indicating that it is NOT hot pressed. A good way to remember the difference between hot and cold press is this: cold press is like skin, it gets “goosebumps” because it’s cold! If the paper is bumpy, it’s cold press.

Plate and Vellum paper

Vellum is similar to cold press, with a bit of a tooth. Plate is smooth like hot press. Rough press paper is much rougher than cold press; it has a super bumpy texture. Traditional vellum paper is made from calf skin and modern vellum is made with plasticized cotton. Vellum is very thin, strong and translucent.

What does mould-made mean?

Mould-made paper is paper that made with a rotating cylinder mould. The mould picks up paper stock and deposits it onto a moving belt to create sheets. The resulting paper mimics the quality of handmade paper. Handmade paper is created using moulds like the one pictured above--handmade moulds are basically wooden frames that hold a screen. The screen picks up the cotton fibers and is the wet sheet is laid on felt squares before pressing. Mould-made papers do not tear as easily as machine made (or Fourdrinier) papers because the fibers are interlocked randomly across the sheet. Most machine-made paper tends to result in fibers laying in one direction.

Key Differences in quality

A good way to illustrate the key differences in paper quality is to think about newspaper versus dollar bills. Newspaper is machine-made, with fibers running in one direction—this is why it tears so easily and cleanly when torn in one direction, but not the adjacent direction. US currency, on the other hand, is made from cotton rag and does not tear easily. You can even wash it in the laundry without destroying it!

Deckled Edges

When artist quality paper has “deckled” edges, this means that the edges of the paper are feathered, rather than cut. This feathering on the edges occurs naturally in the production of paper. The reason most papers (like computer paper) have a straight, clean edge is because most papers are trimmed.  

Watermarks

Watermarks can be seen by holding a paper up to the light. Fine paper manufacturers typically print or emboss their name or logo onto each sheet as a mark of authenticity and quality.

Sizing has nothing to do with the width or length of the paper

Size is a term that means something completely different than what most people think of when they think of size. Size is a mixture, usually of gelatin (yes, like the kind used in cooking) and water that is added to paper to prevent it from completely soaking up paint or other mediums. Some manufacturers, like Fabriano, use non-animal-based sizing in their papers. Sizing a paper changes its absorbency. Papers that have not been sized are much more absorbent. Sizing helps keep paint on the surface of the page.

Papers may have internal or external sizing. Internal sizing is added to the mix while the sheets are being formed. External sizing is added to the outside of the paper after the sheet has been formed. External sizing is very important in making mediums appear sharper and more vibrant on the surface of the sheet. Many watercolor papers are “hard sized,” meaning that they have a lot of sizing added to keep applied colors from feathering and bleeding. Hard sized papers allow paint to dry more slowly

Sometimes the final step in creating a sheet of fine paper is burnishing. When paper is burnished after sizing, it has a smoother and shinier surface. Agate stone was traditionally used for burnishing but paper can now be rubbed by machine.

Rag Paper

100% cotton rag paper is completely made from cotton rags, with no other fibers added. Paper labelled as “rag paper” will always have some rag in the formula, but may also contain wood cellulose.

Woodfree or Wood Sulfite paper and High Alpha Cellulose

Woodfree paper is made from chemically treated wood pulp. It becomes “wood free” because the chemicals strip away everything that is not cellulose. High alpha cellulose means that a paper contains as much as 93% cellulose and is of the highest quality. This type of paper is good quality, but should be avoided for archival work because the use of chemicals in the manufacturing process can affect things such as pH level. Paper that can last for centuries is called “archival quality paper;” it is typically made of 100% cotton rag and it is made without the use of chemicals.

pH and Acidity

Acid free paper is paper that is made without the use of chemical bleach or alum. pH neutral papers are actually less desirable than pH alkaline papers for archival work.

Optical Brighteners

Optical brighteners or OBAs are chemicals added to paper to make it appear whiter. OBAs have a slight blue tint; these “bluing” agents counteract the natural yellow tint of wood cellulose fibers. However, OBAs increase acidity and reduce paper quality over time.

Paper Weight

Heavier papers can handle more medium on water without buckling or falling apart. Generally, the listed weight indicates how heavy one ream, or 500 sheets, of the paper weighs. Using gsm (grams per square meter) is a more accurate measure of paper thickness because different paper types and brands use different standard sizes for measuring weight. Look at the gsm—the higher the number, the thicker the paper.

If this post has you feeling inspired to make some paper-based artwork of your own, check out our Plaza Paper Department!