how to test watercolor papers
There is a special pleasure in every encounter with a sheet of new, high quality watercolor paper. Each sheet has a complexity and sensuality that give it a unique character, and will be your long suffering partner in the making of a new painting.
Watercolor papers are the only really substantial part of a painting the dried surface residue of gum and pigment powders in most paintings would barely fill a teaspoon. Paper embodies the painting, and this body defines how long the painting will live and how favorably it will impress the viewer.
Many watercolor painters are not aware that quality papers are more durable than fabric or wood supports. Historical oil paintings often suffered from decaying canvas or wood supports and were salvaged by cementing the painting to a fresh support under heavy platen pressure, a conservation practice known as lining. In contrast, the paper behind many etchings or drawings from the same period, properly stored, looks as fresh as the day it was made.
Recent improvements in the lightfastness of watercolor pigments mean that today's watercolor paints can last unchanged for centuries. So paper quality and durability should extend at least that long. The standard here is archival quality paper with (1) an acid free or pH neutral furnish consisting of (2) pure cellulose fibers free of extraneous vegetable matter. Poor quality papers, newsprint or "student" papers are as important to avoid as poor quality paints.
As I learned to paint, I discovered that there are no standard procedures that watercolorists can use to evaluate the quality of art papers. In fact, most artists simply rely on manufacturer marketing and brand reputation, retail availability, surface attributes such as texture and color, and the overall experience of painting with the papers.
These artists may be unclear about what makes two papers different, simply because they didn't make the same painting on both and were focused on making paintings, not evaluating paper attributes. They have no reliable way to compare quality, and therefore value for money. And two artists with different painting styles lack a common frame of reference they can use to discuss paper attributes, because they make different demands of the same paper.
The benefit of testing papers especially if you are just starting out painting is that paper attributes become familiar to you, and your knowledge of paper quality becomes more accurate and trustworthy. The tests sharpen your awareness of paper attributes that can assist or thwart your painting intentions: that annoying blotching and dull color is not your fault, it's the paper!
No matter how you learn about and evaluate papers, I urge you to put your observations in a notebook. First impressions and accidental observations are easy to forget or to attribute mistakenly to another paper brand or to a different weight or finish. It's much easier to review your notes than to evaluate a paper all over again.
paper test instructions
Watercolor papers have nine principal attributes, and these define what you need to understand about any brand of paper you use:
they add an essential background brightness that displays paint colors accurately
whether white or tinted, the color is subdued and pleasing and does not yellow or fade when exposed to sunlight.
they provide a flat, flexible surface and handsome physical presence to brush and eye, which includes the surface texture, the weight, and the deckling around the edges of the sheet
they have external and/or internal sizing to control the absorption and retention of water; paints do not blotch or soak outward due to excessive absorbency, and paint edges remain crisp after they have dried
they retain wet strength and dimensional stability (they do not disintegrate or excessively cockle when completely saturated with water)
they are responsive to all paint application techniques, including all types and sizes of brushes, dilutions of paint, types of pigment, wet in wet methods and multiple glazes
they resist damage from editing techniques (scrubbing, blotting, scraping, erasing) and the removal of resists (latex compounds, rubber glue or masking tape)
they bond securely with the paint vehicle and pigment, and display dried paint colors accurately and in the full chroma and tonal range (color gamut)
they can be effectively used with a variety of related media, including graphite or charcoal, watercolor pencils, pastels and/or acrylic paints; and
they are archival (they will not change color, flexibility or strength over time due to chemicals in the paper, mounting or air), which means they will last unaltered for centuries under proper care and storage.
After considerable research and some trial and error I devised the following tests to bring out these paper attributes as vividly as possible. If you look for any additional or specific paper traits, be sure to include them in your tests.
1. Prepare test materials. First read through the test procedures below to get a sense of where you're headed. Then assemble all the materials or tools you will need to do the tests. Everything you need for my tests is listed in the following table.
2. Select a test sheet. Paper testing should be done with similar paper samples. I prefer to use a full sheet (22" x 30") of 300 GSM paper, as that is a standard format and weight available from almost all paper manufacturers. Use a lighter or heavier basis weight if that is what you paint on.
Use a fresh sheet straight out of the packaging. Don't use a sheet that has been lying around the studio and may be soiled or damaged from previous handling or discolored by light exposure. (You'll discolor the sheet as part of the test!) Handle the paper by gently holding it edgewise between your palms (like a sheet of glass), or better pick it up along one edge, using a folded sheet of stationery or notebook paper placed over the edge of the watercolor sheet and under your fingers.
Don't test watercolor blocks unless you prefer to use them: they typically have a less pronounced surface texture and a more heavily sized finish, and many brands of watercolor papers are not available as blocks. If you test a block sheet, cut it from the block before you start the testing, so that you can examine rattle, flexibility, and dimensional stability (how much the paper cockles or curls when wet). A standard 10"x14" or 12"x16" block approximates the quarter sheet size used in the tests described here.
3. Flexibility. Slowly fold back one corner of the paper against a metal straightedge or table edge; place the fold diagonally about 2" from the corner. Note the paper's resistance to pressure and its brittleness or tendency to crack along the fold. If the paper surface breaks during folding, note the approximate angle at which this occurs.
Now carefully bend the entire sheet across its narrow width, as if you were going to roll it up, and note how far you are able to do this without risk of damaging the sheet. Immediately let the sheet unroll on a flat surface, and note how much it retains the "memory" of rolling up.
Lower quality sheets are usually brittle to folding and retain the "memory" of rolling up. Better quality sheets will not break under extreme folding and return to flat after they are unrolled.
4. Pulp composition. Holding the sheet by a short edge, rapidly shake the sheet to evaluate its "rattle" or audible stiffness and elasticity. In a dark room, hold the sheet up to a bright light or window, and examine the density variations in the paper caused by irregularities in the furnish or (for handmade papers) in the shaking of the mould during draining. Look for visible areas of lightness (thinness), a lumpy or "cottage cheese" texture, "papermaker's tear drops" (small round areas where light shows through), folds or tears, and (on the wire side) impurities or inclusions (bits of darker fiber or plant matter, hairs, dirt, etc.) that sank against the wire when the pulp was cast.
The best quality paper pulps have been heavily macerated prior to casting and will have a bright, warbling, almost metallic rattle; less intensively processed papers will have a dull, muffled or wooden sound.
Minor variations in pulp thickness are usually acceptable in handmade papers, provided they are not apparent when the sheet is examined under reflected light; but large inconsistencies or pulp thinning toward the edges are undesirable, and any density variations in mouldmade or machinemade papers are a sign of manufacturing problems.
Inclusions were unavoidable in olden times (19th century landscape painters learned to put a flying bird over a fleck of obtrusive gunk under their sky wash) but are always undesirable in modern papers unless specifically added for decorative effect.
5. Watermark and chop. Again hold the sheet up to a bright light, and look for the watermark. Orient the sheet so that the watermark "reads right" (is legible and right side up), and note its location on the sheet. Note the design of the watermark, and any special trademarks or symbols. If there is a chop (embossed words or trademark), note its location as well. If the watermark allows you to distinguish the wire from the felt side, note an "F" or "W" with an indelible pen on the appropriate side of the sheet.
Unfortunately, watermark conventions vary by manufacturer and manufacturing process. In most European papers the watermark is placed to read right when the felt side of the sheet is facing toward you. In English papers the watermark may read right from the wire side and is reversed when viewed from the felt side. As a check, the watermark in handmade and some mouldmade sheets will leave a visible indentation in the paper surface (use slanting light to see this), and this is on the wire side because the watermark is actually attached to the mould. In machinemade sheets the watermark may be embossed by a rubber stamp on the side opposite to the cylinder mould. To check this, wet the sheet: most mouldmade and all machinemade sheets, when soaked, will curl toward the cylinder ("wire") side of the sheet. However, some papermaking machines cast the pulp between two wire cylinders and then feed the web between two drying felts, so the two sides are identical.
There are really two issues that matter. The watermark "read" helps you quickly identify a preferred side of the sheet, and the indentation or embossing will usually be visible in a finished painting. Some artists always paint with the watermark reversed to reduce its visibility, while others like to "fly the brand flag" and paint on the side that better reveals the brand embossing or watermark indentation. Some just put the watermark in a standard location, for example at the bottom right like etchers, and just use the side that makes this possible.
6. Finish. Hold the sheet so that the surface is illuminated at a slanting angle by a strong light, and visually inspect the surface texture of the paper; use a magnifying glass if you have one. Look at the texture elements (weave, wire patterns, bumps, depressions, crannies, lumps and fuzzy tufts). Compare the textures on the felt and wire sides of the sheet (determined from the watermark inspection above) and note any differences in finish or texture between the two sides. Stroke the sheet with your fingertips to evaluate the microscopic texture of the finish.
It is useful to use a standard or favorite watercolor sheet of similar finish (R, CP or HP) as a basis for tactile comparisons and texture description.
A "cold pressed" or "rough" finish will change significantly from one brand of paper to the next, and also across a 185 to a 300 to a 640 GSM weight within the same brand of paper. Note also the obvious difference between wove or laid sheets.
Machinemade papers present an incredibly consistent finish and no visible contrast between the two sides of the sheet. In handmade and many mouldmade papers, the wire side of the sheet has a less assertive, more homogenous and flatter texture, because the pulp settled evenly against the wire mould; however, this is the side where any inclusions will be most visible. The felt side is usually rougher because texture is impressed only by the felt blotter, whereas the wire side often shows an irregular or mixed texture, because the surface was first impressed with the wire mould, then flattened by the felt blanket or metal roller.
Some hot pressed papers show an irregular, very fine "tufting" or extrusion of paper fibers through the exterior sizing. (I think this is caused by individual fibers sticking to the hot calendar rollers as the sheets were pressed.) These will appear in the wash test (described below) as a slight flecking or spotting of the finished wash, an effect that is usually undesirable.
7. Grain. Using a deckle ruler or metal straightedge, fold and then tear the full sheet into quarter sheets. Note the strength of the paper torn in each direction: the direction that tears easier is "with the grain," that is, in the same direction as the lengthwise orientation of the cellulose fibers. Examine one of the "across the grain" tear edges under a magnifying glass to assess fiber size and length: papers made with short fibers will look "fuzzy" and very even at the tear, longer fiber papers will look "hairy" and more ragged.
Handmade papers do not have a noticeable grain. All machinemade and most mouldmade sheets have a noticeable grain because the fibers are aligned downward by gravity as the pulp is pulled upwards by the rotating mould cylinder; this causes the cellulose fibers to lie parallel to the two edges perpendicular to the cylinder axis. These usually have the "natural" deckle edge along the long (30") sides of a full sheet. The "deckles" along the short sides are produced by tearing the sheet with a dull blade or cutting with a high pressure jet of water.
The heaviest (400 to 640 GSM) sheets cannot be conveniently torn without first scoring the sheet with a dull blade, then wetting just the fold with a stiff sponge before tearing.
8. Color. Under moderately strong white light (mid morning or mid afternoon outdoor sunlight is best), lay a white standard next to the watercolor sheet, and look at the difference in lightness and tint. If you are testing more than one type of paper, lay the sheets side by side on the ground in open sunlight, then indoors on the floor under strong artificial light, and judge the color and brightness of the papers in each situation.
I prefer to lay the sheets on the ground, as paper color can change depending on the angle of illumination and view, which is best observed by walking around the paper samples. I lay the papers on a plain white bed sheet spread outdoors on the ground; this adapts my eyes to small brightness differences between the papers. Tinted sunglasses can also reveal color differences.
Your white standard can be a sheet of pure white construction paper, your favorite sheet of watercolor paper, or a small canvas or board painted with several coats of matte finish titanium white paint. The standard should be as close to the same size as the quarter sheet as possible, to provide the best visual contrast; photographer's gray scales are too small. It is not desirable that the standard be a brilliant white, because this will make an acceptably white paper appear gray, but it should be a balanced white without perceptible brownish or bluish tint.
9. Pulp Composition and pH. With scissors, trim off a corner of the paper about 1" wide. Ignite one end of the paper with a match or stove, and set it down to burn in a cigaret ash tray or saucer. Use a pH test strip or test pencil to assess the acidity of the paper.
Pure cotton or linen cellulose, properly sized and with no fillers, will burn completely to a fragile, whispy white ash. Any ash that is dark, brittle, heavy or only partially consumed indicates the presence of wood (lignin), noncellulose or synthetic fibers, heavy sizing, fillers such as clay, or additives such as calcium carbonate.
pH is a measure of the acidity or alkalinity of a substance (specifically, the proportion of hydronium H3O+ or OH- ions released in solution with water). A pH of 7.0 is neutral; acids have a very low pH of 0 to 4, and bases a high pH of 10 to 14. Art papers should either be neutral (pH = 7) or if buffered slightly alkaline (pH of 7.0 to 8.0). In cellulose papers, values below 6.5 or above 8.0 are undesirable.
It is relatively simple and inexpensive to conduct your own pH tests on watercolor papers, and this should always be done if you suspect the manufacturer has misrepresented their product or if the papers are old. Papers that start out as pH neutral can become acid because of chemical residues in the paper or absorption from the atmosphere.
pH test strips with test instructions are available from a few sources, including Micro Essential Laboratory and Talas (search for "pH test" at each site to get a listing of products). You can measure paper acidity with paper pH test strips, with a digital pH meter, or with a nifty little tool called a pH pencil. Talas has the meter (which requires a special testing solution); both MicroEssential and Talas have the test papers and pencils. If you choose limited pH range papers make sure these adequately bracket the neutral values (are sensitive to pH between 4.5 through 8.5 or 5.0 through 9.0).
Specific test methods depend on the test materials you use. In general you want to wet a small area of the paper with one or two drops of distilled water, allow the water enough time to soak into the paper and dissolve the internal sizing (about 2 minutes), then apply the test material while the paper is still moist. The pH is determined by comparing the color of the test material to a pH key. Repeat the test to confirm the accuracy of your results, and use the average if the results differ.
10. General permanence. There are two separate tests for the long term durability of the paper: embrittlement and yellowing.
Place a 6" square sample of the paper on the middle rack of an oven, and on the bottom rack set a cake pan filled with 1" of water. Set the oven to 90°C (190°F) and let the paper "cook" for 72 hours. The paper will have approximately the same attributes as paper stored for 1000 years under archival conditions.
Place a sample of the paper in a lightfastness frame and set in a sunny, south facing window for about two weeks. The paper will yellow rather quickly if it contains any wood lignin.
11. Absorbency. Lick the paper to gauge the absorbency and fine texture of the surface. Lay the sheet on a flat surface, apply pure water with a single stroke of a saturated 1" flat acrylic brush, and observe the amount of time until the water is completely absorbed.
To evaluate cockling, completely cover one of the extra quarter sheets in warm water for five minutes, remove and hold by one corner until drained, then lay on a flat surface (kitchen counter or painting board). Note the extent of cockling, and any pattern in the cockling (parallel cockles, curling of the entire sheet) as the paper dries.
Strongly absorbent papers papers with little or no surface sizing and/or a heavily macerated furnish will seem to stick to your tongue. They will also cockle more visibly under the water brush stroke and after soaking. Machinemade papers will characteristically curl up when wet. Papers that cockle excessively when soaked typically have longer paper fibers, were more extensively beaten in the pulp stage (which causes the cellulose fibers to absorb more water and to bond firmly with each other), and were air (loft) dried (which allows the wetter cellulose fibers to bond to each other more extensively during the slow drying time).
The following tests require you to do a variety of painting, lifting, scraping, masking, sponging and drawing tests on the quarter sheet. The diagram shows a suggested layout for these tests, numbered as in the text.
suggested layout for watercolor paper tests
shown on a quarter sheet format (11" x 15"); numbers refer to testing steps
There should be sufficient room on the sheet to rearrange the tests if you like, or add other tests that interest you; the various watercolor paper tests described by Ian Sidaway may give you some ideas.
These tests are described in the order in which you perform them, followed by comments on interpreting the tests after all the steps have been completed and the sheet has completely dried. Always test the sheet in landscape orientation, on the side you prefer for painting (usually the felt side, or the side that makes the watermark less visible).
12. Resists and Masking Tape. Apply resists to the paper near the upper right corner. I use a 3" long strip of 1/2" masking tape, burnished firmly to give a crisp edge, and two or three painted stripes of masking fluid (liquid latex, rubber cement or Maskoid). These should be placed so that they will be completely covered by the ultramarine wash (test 14).
13. Graphite Pencil and Erasure Damage. Next to the resists, near the top edge of the sheet, make several parallel lines on the paper, using the brand and hardness of pencils and/or charcoal you normally use for layout, design or drawing with watercolors. Make the lines only as dark (with as much pressure) as you normally use. Then gently erase the center 1/3d of the lines with your usual eraser. (Most painters use a gray kneadable eraser.) Stop erasing when the graphite has been completely lifted, or when the erasure begins to visibly damage the paper.
14. Wash Application. Make a mixture of equal parts ultramarine blue (PB29) and either cerulean blue (PB35) or cobalt violet (PV14), diluted to roughly 1 part paint to 8 parts water.
Lay the paper on a painting surface tilted to a 15° angle, with the resists and masking tape at the top. With a 1" squirrel or kolinsky flat wash brush, paint an even wash over the righthand side of the sheet, starting from the top edge and working steadily down to the bottom edge. Paint in slow, long, even, parallel strokes with light pressure; do not scrub or retouch. After each of the first three strokes, stir the wash mixture thoroughly (to bring up the granulating pigment) and replenish the brush in the wash mixture. From the fourth stroke to the bottom of the page, add no more paint to the brush, but continue painting down the sheet with the existing wash bead until the area is completely covered or the brush goes dry completely dry.
At this point, let the sheet dry thoroughly. Note the amount of curling or cockling in the sheet while it is wet, and how far the sheet returns to complete flatness after it has dried.
Carefully remove the resists and masking tape, and overpaint part of the reserved areas with the quinacridone magenta solution (used in the next step) to test the paper absorbency after the lift has been removed.
The granulating cerulean blue or cobalt violet paints tend to collect along the bead after each wash stroke, making it harder to get an even wash texture. That is the point: they reveal the properties of surface texture and paper absorbency.
Examine the wash area carefully for any blotching or spotting in the color. The manufacturing standards of commercial art papers have declined in recent years and blotching is a sign of pulp impurities or surface sizing that was improperly applied.
Resists should lift cleanly and without tearing or fuzzing the paper surface.
Absorbent papers will exhaust the available paint before you can complete the wash to the bottom. Hard or heavily surface sized papers will usually allow a complete coating of a quarter sheet.
15. Backruns (Surface Sizing). Lay the paper flat, and with a 3/4" acrylic flat brush, paint three juicy strokes of a strongly blossoming pigment, such as dilute quinacridone magenta (PR122), iron blue (PB27) or dioxazine violet (PV23), at the top edge of the lefthand side of the sheet. Leave the paper flat, and let the paint completely dry.
Backruns indicate the paper is relatively nonabsorbent, as the paint dries on the surface rather than into the paper; however light basis but absorbent papers can also produce backruns if they become saturated. Hot pressed or bristol finishes tend to produce the most backruns, rough finish or toothy etching papers the least.
16. Scraping (Dry Lifting). Scrape clean a small area (about 1/4" by 1") of the ultramarine wash with a razor blade or X-acto knife, to assess endurance of the paper to dry lifting.
Scraping will inevitably produce some surface damage, but this should clean up to be almost indistinguishable from an unscraped surface. Papers made with very short cellulose fibers tend to yield a fuzzy surface that is difficult to clean up.
17. Blotting (Wet Lifting). With the paper completely flat, use the 3/4" acrylic flat brush to paint one horizontal stripe of a moderately staining paint, such as dilute permanent sap green, below the magenta area.
When this area has completely dried, use the rinsed acrylic brush wetted with clean water to completely lift a 1" section of the sap green by gentle downward scrubbing, blotting up dissolved paint with a paper towel. This should be done without letting the paper dry, and continued until either the paint is lifted completely or visible damage occurs to the paper surface.
When this area has completely dried, paint a second stripe of sap green below and partly on top of the area of lifted pigment, to test the paper receptivity to paint where the paper was scrubbed.
18. Sponging. Using a natural sponge soaked and then wrung damp, scrub the lower left area of the sheet with five firm, downward strokes of the sponge. Let dry completely. Then use the remaining ultramarine wash solution to paint an ultramarine wash over the area scrubbed by the sponge.
19. Paint Saturation. Lay the test sheet outdoors under full sunlight or indoors under strong artificial light, using the large sheet of medium gray construction paper as a background, and evaluate the color and brightness of the painted test areas.
Look for any irregularities in the wash areas, for any traces of machine markings (such as roller tracks) across the paper, and for visible traces of the sponge scrubbing under the wash areas.
Colors should appear fresh, bright and clean. Excessively absorbent papers will yield a dull, blotchy color; yellow or brown papers will have an especially dulling effect on green, blue or violet paints.
Now let's review how to interpret these tests. As demonstrations, here are photographs of two completed test sheets.
twinrocker 640 GSM CP white watercolor paper
Let's first look at one of the best performing sheets, from Twinrocker.
1. The ultramarine washes are very even: there's little noticeable banding from the cobalt violet, and the righthand wash mixture carried all the way to the bottom of the sheet. This indicates the paper is not strongly absorbent, and has a good surface coat of sizing it did not exhaust the alotted amount of wash mixture before the wash was completed.
2. The resists lifted cleanly and the magenta stripes show that the paper underneath was not scarred. The scraped area is clean, without tearing or shredding at the edges. The paper is very suitable for these techniques.
3. The magenta area (upper left) is beautifully even, without a trace of blossoming. This again indicates that the paper is moderately absorbent; the sizing is perfectly balanced, and the surface texture did not pull an excess amount of paint out of the brush. The paint was able to even out and dry before capillary action caused backruns to form.
4. The sap green stripe lifted cleanly, and the stripe painted underneath shows almost no visible damage to the paper. The paper is very suitable for limited wet lifting, and this again suggests a good coat of external sizing.
5. The lefthand ultramarine wash is completely smooth and shows no traces of the sponging that preceded it.
6. Viewed in strong light, the paint colors are bright and true, with no apparent bias or dulling caused by the support. There are no apparent roller marks or variations in the sizing or paper pulp.
In your notebook, these observations would be added to those obtained in steps 1-11 above.
fabriano artistico 640 GSM CP watercolor paper
Let's next look at a sheet that fared less well, from Fabriano.
1. The ultramarine washes are fairly even, although there is noticeable banding from the cobalt violet, and the wash beads had a tendency to "drool" or continue draining down the sheet. This suggests a relatively heavy amount of external sizing that dissolves slowly when wet. The wash mixture also did not carry all the way to the bottom of the sheet, but not because the paper was highly absorbent but because of the stronger surface texture. The pencil mark washed partly away under the brush, another sign of surface sizing.
2. The resists lifted cleanly but the magenta stripes reveal minor scarring of the paper surface. (Note the backruns in these painted areas.) The scraped area was clean, without tearing or shredding at the edges.
3. The magenta area (upper left) shows substantial backruns and irregularities caused by the individual brush strokes. This again indicates that the paper is not very absorbent and has a somewhat insoluble external sizing.
4. The sap green stripe lifted cleanly, although a lot of paper lifted along with it, making it hard to decide whether the lifting happened because of paper friability or hard external sizing. But after the excess paper was brushed away and the paper was allowed to dry, the stripe painted underneath showed almost no visible damage to the paper. The paper is suitable for limited wet lifting.
5. The lefthand ultramarine wash is heavily marked by the sponging that preceded it; the small black clots of color are balls of paper fiber rolled up but not detached from the surface by the wet sponge.
6. Viewed in strong light, and set next to other sheets, the paint colors are somewhat grayed. Minor variations in the surface sizing were noted in some sheets.
Although not described here, it is important to also test the paper's acidity and general permanance, as described in tests 9-11 above.
For the tests reported in the guide to watercolor papers, I photographed the felt side of the paper with a Kodak digital camera, using the macro lens at 8" from the paper surface, under a righthand downward slanting halogen lamp. These photos are reproduced in the guide to show the many subtle variations in finish across different brands and weights of paper.
Some brands of watercolor paper, and handmade papers in general, may show occasional variation in paper quality or paper attributes from one lot to the next. I have not assessed the consistency in paper manufacture, but in general it is quite good. The main problem you will encounter is occasional blotching of the surface sizing with impurities (excess sizing or some oily contaminant) that will repel a wash application.
The results of these tests should help you identify the types of paper you may want to try for yourself. But you must make the final determination based on your experience painting on the papers yourself!