Watercolor paper is perhaps the most significant aspect of watercolor painting even more so than the watercolor paints.  Therefore, it is appropriate to discuss watercolor paper to better understand how it is made and their properties.

Watercolor paper is a special type of paper made with cellulose. The cellulose can be derived from many sources but typically watercolor papers are made from the cellulose derived from cotton and/or wood pulp. Cotton is much stronger than wood pulp and is also pH neutral, meaning it is naturally acid free.  Watercolor paper with more cotton content therefore is better for its strength and acid free properties. 

Better quality watercolor paper is made of cotton fibers or cotton linters. These organic fibers are turned into a pulp, which is then placed into the paper making machine, pressed flat, dried, and turned into sheets. So what’s the difference between cotton fibers and cotton linters. Cotton fibers are extracted from cotton material and are long and much stronger. Cotton linters, however, are short fibers that are still attached to the seeds after initial processing and not as strong. Linen rag has long, thin fibers which interlock with the cotton fibers, increasing the paper’s strength. This makes the paper particularly robust and resistant to repeated reworking of paint on the surface. The cotton pulp is extracted from the leftover scraps of cotton fabrics or recycled cotton rags. It is then ground into a pulp and converted into a cotton paper. The higher the grade of the paper, the more cotton fibers it contains. The best paper for watercolor is 100% cotton fiber. 

A handheld paper mold is made of two separate parts – the mold and the deckle. The mold is covered in a metal mesh (usually a bronze mesh, which is flexible and non-tarnishing), while the deckle is a removable wooden frame which sits on top of the mold and creates the edge of the paper. A deckle edge is an irregular edge which occurs when the paper stock goes between the mold and the deckle. Because handmade sheets are individually formed, they are the only papers that have four genuine deckle edges, one of the most beautiful characteristics of handmade paper.

Each sheet is formed by dipping the mold and deckle into a vat of the paper stock.  As water drains through the mesh it leaves a mat of fibers on the face of the mold. The sheet, while still in the mold and deckle, is lifted onto a vacuum bed which removes some of the excess water. The sheets are then couched (sandwiched) between wet woolen felts and pressed with a hydraulic press to remove more water. After couching and pressing, the sheets still contain around 50% water and they are hung to dry.

When mold made watercolor paper is dried it is either pressed using a press or a roller is rolled on it.  The paper with maximum surface roughness or texture is called ‘Rough’. This is generally rolled or pressed between a felt cloth. Rough paper is additionally pressed using a mechanical press with finer grains or rolled with a roller covered with felt cloth of finer texture then what is used to dry Rough paper. This is called ‘Cold Pressed’ ( in some places it’s called ‘Not’ ).  When paper is additionally dried from a smoother heated roller surface the finish is called ‘Hot Pressed’. 

Surface Texture

“Rough” watercolor paper is loosely compressed, which means, just like it’s called, it has a very rough surface. The rough watercolor paper is great for landscape painting and wet on wet as well as glazing techniques. It allows the pigment to penetrate deep into the paper, resulting in more vibrant colors with each additional layer application.

“Cold-pressed”, moderately rough surface and allows an excellent water absorbance and pigment penetration. This paper is excellent for various painting techniques, including wet on wet as well as dry on dry. Cold press is ideal for landscaping as well as finer detailing. It is the most popular among the majority of watercolor painters.  

“Hot-pressed” watercolor paper is very compressed during the making process, resulting in a very smooth surface. Hot pressed paper won’t work well with wet on wet and glazing techniques. Not much pigment will seep into the paper, and will just sit on the surface. It is, however, great for dry on dry fine detailing techniques, inking, and calligraphy. It is also great for gouache painting.

Sizing

Sizing is an additive used to alter the absorbent qualities of paper. Watercolor paper absorbs paint directly into the fibers faster without sizing. Traditional sizing uses gelatin, but plant-based and synthetic sizing are also commonly used. Sizing can be applied internally, externally, or sometimes both. Sizing is a key ingredient in the production of watercolor paper. Paper is a naturally highly absorbent material, and the addition of a sizing agent makes the paper partially water-resistant. As well as containing an internal synthetic sizing watercolor paper is sized externally by pulling sheets by hand through a tub of hot gelatin. This allows wet paint to be moved around on the surface and remain vibrant and crisp when dry. It is ideal for lifting techniques because the color does not saturate the fibers of the paper and is more easily removed. External sizing also increases the surface strength of the paper, allowing it to withstand more vigorous painting techniques, like scrubbing and reworking of the paint.

Weight

Completed watercolor paper is normally in sheets of full imperial size 22” X 30 “.  It is stacked in a ream of 500 sheets. The term called pound per ream or just Lb. is defined as the weight in pounds of 500 sheets. Thicker watercolor paper can withstand rough use, buckling and bending due to the effect of water. Hence watercolor paper is normally specified according to its thickness as the weight of a 1 x 1 meter of paper in grams using a term called Grams per Square Meter or GSM or in terms of reams weighed in pounds, #. Watercolor paper is normally found in one of three thickness weights: 90#, 140# or 300#. 

Final Note

Watercolor paper absorbs water, but it is not continuous, it is partitioned so that the sponge characteristics of adjacent surface areas are independent. Moisture flows from greater moisture saturation to lesser moisture saturation between sponge areas. The key to control in watercolor painting is to regulate the differences in moisture saturation between your sponges. You can think of a piece of watercolor paper as an almost infinite number of adjacent sponge areas. Therefore, understanding watercolor paper and the differences of choices of products is very significant and the choice of watercolor paper will effect successful painting.