Paper Parameters

Like most watercolor artists, I’ve spent a good bit of time trying out different paper.  Although I’ve found paper I like, it’s expensive – so every sale makes me wonder if the grass might be greener on the other side of the deckle edge.  Any watercolor teacher will tell you to use paper that’s 100% cotton and good quality, but beyond that – what are the characteristics of good paper that I like? What other parameters for evaluating paper are there?

Me being me, these questions motivated a deep dive into the world of watercolor paper manufacturing.  I learned a lot – and I also got a peek at how much more there is to find out. I’d LOVE to tour a paper factory or talk with someone in the industry, and I plan to keep working on those goals as well as testing paper in some new ways.  In the meantime, I’ve learned that watercolor papers differ in key ways defined by their ingredients and production methods. This is a long post. If you just want the key takeaways without the whys and hows, scroll to the bottom!

Paper “Ingredients”

Paper is made from a slurry of ingredients (called “furnish”) beaten with water.  The main component of furnish is, of course, cellulose.  Usually the cellulose is from either cotton or trees.  Cellulose from trees contains acidic lignin which repels water and causes paper to yellow and disintegrate.  The lignin can be removed and/or made ph-neutral by treating it with chemicals and washing it.  Treated cellulose might be listed on paper packaging as “ph neutral,” “alpha cellulose,” or even, confusingly, “wood-free paper.”  These papers may still contain some acids and residual chemicals, and will not have the same strength and absorbency as cotton papers.

Cotton is the cellulose of choice for watercolor artists, as it is more absorbent, better resists scrubbing, and is naturally acid free.  Cotton for paper can come from “rag,” which is made from scraps from recycled clothing or clothing manufacturing or from long-fiber cotton that could be spun into thread; or from “linters,” which are short fibers that remain stuck to the cotton seed after the longer fibers have been removed.  Linters are separated from the seeds by cooking them with solvents as part of processing the seeds for further use as food and cosmetic products, and sold as felt-like sheets. Linters are more absorbent but less strong compared to rag.  Some paper brands, such as Arches, are made entirely from linters, while others contain a mixture of linters and rag.  Paper labeled as “rag paper” can contain varying amounts of rag mixed with other cellulose from cotton or even wood.  Cotton rag may be treated with acidic chemicals to aid breakdown and whitening, so look for paper labeled “acid-free” AND “100% cotton.”

Besides the cellulose, paper may contain a variety of other ingredients:

Buffering – this is a basic chemical, such as calcium carbonate, added to neutralize future exposure to acids from air pollution.  My research is mixed on whether slightly basic paper is good or bad for the longevity of paint.  Some people think it could cause changes to some chemically-sensitive pigments, especially Prussian Blue, but it should be fine for most pigments and might be a good addition if you’re very concerned about longevity. 

Fungicide – Arches and Saunders-Waterford are two common paper brands that contain fungicide to inhibit mold growth in humid environments.  Since most of us do not use sterile water when we paint, there is the potential for introducing organisms to our art.  Hahnemuhle, Fabriano, and Master’s Choice do not use fungicide, and Hahnemuhle states that cotton paper naturally inhibits mold.  This was an ingredient I was a bit surprised about – and I wonder about the artist’s exposure to fungicide.  It’s something I’d like to look into further.

Whitening – “Bright white” papers have some sort of whitening or brightening added (natural cotton is a warm off-white). Some papers use optical brightening agents (OBA), which are fluorescent dyes that absorb and emit UV light to make the paper look whiter.  As we’ve learned previously, fluorescent dyes fade very quickly, which means your paper, and the paint on top of it, will change color.  You can check for OBA by shining a UV light on your paper.  If you want whiter paper, look for papers that are whitened using Titanium Dioxide pigment, which is stable long-term.

Sizing – this glue-like additive strengthens the paper and prevents paint from wicking right through the sheet or “sinking.”  While most paper we use is sized, watercolor paper requires more sizing than your average copy paper.  Paper that has less sizing is “soft” while paper with more sizing is “hard.”  Harder-sized paper will keep more of the pigment on the paper surface and thereby make it easier to create hard edges and lift or scrape off paint; provide brighter colors; and dry faster (making smooth washes more difficult).  How much sizing is “just right” is very much a personal decision, and a big difference between paper brands.  “Internal” sizing is part of the furnish, mixed with the paper pulp.  Most brands I could find information on use the synthetic sizing alkyl ketene dimer (AKD) for internal sizing, which is derived from fatty acids (and is vegan). “External” sizing is applied after the paper is made either by dipping the paper in a vat of sizing and allowing it to soak in (tub sizing), or by spraying sizing over the surface.  This creates harder sized paper than those with only internal sizing.  Tub sizing also gets more sizing into the paper than spraying.  Gelatin is the most common external size.  Although there are vegetable gelatins, unless stated otherwise it’s safe to assume the gelatin is made from boiling animal skin or bones which are waste products from the meat industry.

Paper Manufacturing 

Paper can be made using three different processes: handmade, mould-made, and machine made.  

Machine made paper is made with a fourdrinier machine, which sprays paper pulp onto a continuously moving screen conveyor belt creating a continuous length of paper.  As the paper moves through the machine, it is drained, pressed, and dried using a series of different rollers.  These machines can make many thousands of sheets per hour.  The high-speed injection of the paper pulp onto the screen aligns all the cellulose fibers in the same direction, creating a strong “grain” to the paper.  This will cause watercolor washes to run more in one direction than another, causes it to curl with the grain when wet, and makes the paper slightly less strong. The texture of the screen and rollers creates the texture of the paper.

Mould-made paper is made with a cylinder mould machine.  Large cylinders made of wire screen are partially submerged in a vat of paper pulp, pulling a continuous sheet of pulp out of the vat as they slowly rotate.  The sheet is transferred to a piece of felt, drained, and pressed with felt-covered rollers (for cold pressed) and/or heated, smooth rollers (for hot press). The texture of the paper is determined by the felt texture, although the wire texture of the cylinder is also still visible on rough and cold press papers.  Machines that use natural, wool felt provide the most random and unobtrusive texture.  Rough paper may not be pressed or be pressed less, and because of this the fibers may expand more when wet, causing more cockling.  Mould-made paper is usually air-dried on large rollers in a heated room, in single sheets, or in stacks.  Stacked paper and paper held under tension on rollers develops less texture.  Slowly air drying makes paper that cockles less. Cylinder mould machines make a few hundred sheets an hour.  Because the cellulose fibers are pulled slowly from the vat of pulp, the paper has very little grain making for more even washes and little curling.  Most instructor-recommended watercolor paper brands are made in this way.

Handmade paper is lifted one sheet at a time from a vat of pulp, using a large screen inside a wooden frame held by a skilled paper maker.  The frame is gently shaken from side to side to ensure the fibers are randomly aligned and there is no grain.  The sheet is then transferred to a piece of felt, and a stack of paper can be pressed to remove water.  The finished sheet is then air-dried.  Some papers are never pressed, leaving more of the natural pulp texture and making for some of the roughest papers available.  Other paper is “calendared” or run through weighted and/or heated rollers to smooth the texture. Several people working together can make around 80 sheets per hour, which is why handmade papers are the most expensive.

Phew! That’s a lot of variables! To summarize, here are:

The Parameters To Consider When Choosing Paper

• Cellulose Source Look for paper that’s acid-free AND 100% cotton. Don’t get confused by labeling of inferior sources such as “rag paper” or “wood-free cellulose.” If strength and durability is important, look for paper made with cotton rag AND linters.
• Additives If longevity and archival qualities are very important or if you live in a warm, humid climate consider looking for paper with buffering and fungicide. If you are concerned about exposures to toxins, maybe avoid those fungicides! If you want bright white paper, look for paper whitened with Titanium Dioxide, not OBAs.
• Sizing If you want hard-sized paper for durability, hard edges, brighter colors, and easier lifting; look for paper that is externally sized using gelatin, preferably using the tub sizing method (it will probably be internally sized also, which is good). If you want softer edges, smooth washes, and paper that stays wet longer, go for a softer paper that just has internal sizing. This is also your best bet if you want to avoid paper made with animal products, as internal sizing is generally synthetic.
• Manufacturing Method Choose mould-made or handmade paper so it will have little or no grain (although machine-made 100% Cotton paper could be OK for practice and tests, and in smaller sizes where curling can be more easily controlled.)
• Felt Texture Unless you’re buying smooth, hot press paper, look for paper made with natural wool felts that will have a random texture. If you want the roughest paper, look for handmade, unpressed sheets.
• Drying Method Look for air-dried papers that will cockle less.

To find this information, your best bet is looking on the manufacturer’s website. Art retailers don’t always elaborate on all of these perimeters. Jackson’s Art provides this very useful chart that compares most of these data points for many common brands. A favorite of mine, Master’s Choice, is missing, so here’s all the data on it as an example of the kind of information you can expect to find: it is acid free, 100% cotton (they don’t state if it’s from rags or linters, so it’s probably all linters since rag is usually a selling point), they don’t say it HAS buffering or fungicide so it probably doesn’t, it’s not whitened, it’s internally and externally sized with gelatin, mould-made with natural wool felts, and they don’t state the drying method.

Hopefully this helps you better evaluate paper to find what you need!

Selected sources – watch the paper making videos! They’re fascinating!

• Handprint by Bruce MacEvoy
• Jackson’s Art “Everything You Need to Know About Paper“
• Watch paper being made on a cylinder mould machine at Fabriano
• Watch paper being made by hand at Fabriano

And check out my previous post, Watercolor Paper Myth Busting for even more things you didn’t know about paper!