— Frank Ippolito ©1993
This article appears in the 1993 Journal of Natural Science Illustration (Vol. 2, No. 1)
Editor’s Note: The 2010 reissue of this article is a modification of the original. Two of the illusrations are replaced with different subject matter fro purposes of better color reproduction. All illustrations in the original print edition are in black and white.
The field of Scientific Illustration often demands the production of highly detailed, accurate renderings that must survive the less-than-perfect world of photographic reproduction. The collaborative efforts between artist and researcher/author require the illustrator to adopt a most flexible approach so as to accommodate the likely revisions that are inherent in such arrangements. Additionally, it is the nature of the illustration field to impose deadlines that preclude the use of time-consuming approaches and techniques, favoring instead those media that can be handled with relative speed. Gouache is a medium that addresses these concerns and is an excellent choice for scientific illustrators finding themselves challenged by these considerations. Gouache is perfectly suited for precise, detail-oriented paintings in both full color and black and white. Its predictable tonal quality, vibrant hues, and fast drying time combine to make it a popular choice among designers and commercial illustrators. Opaque qualities allow for the layering of details that permits multiple revisions, and because of the picture's flat surface it is easily reproduced photo-mechanically.
Derived from the French word meaning opaque, gouache (gwåsh) draws its origins from the Middle-Ages. For the preparation of illuminated manuscripts, artists began to introduce glue into their water-based media. Over time it was discovered that the addition of chalk powder or zinc white provided an opaque paint which had strong covering power. Although not as well known a fine arts medium as oil paint or watercolor, there are many examples throughout history of gouache being used as such with good effect. Dürer, Degas, Van Gogh, and Picasso are but a few of the names associated with this versatile paint.
WHAT IS GOUACHE?
Gouache is opaque watercolor. It is manufactured in much the same way as transparent watercolor. While they both are comprised of pigment, wetting agent, and a binder, gouache additionally receives an inert white pigment and higher levels of concentrated pigment. The result is a paint with a smooth, matte finish that can be at times almost velvety in appearance. It can be used in conjunction with other water-based media such as acrylic, transparent watercolor, ink, and markers, as well as the dry media of pastels and color pencil. Because the pigment is finely ground, gouache also is well suited for use in an airbrush.
It is my experience that artists often discover opaque-watercolor after having spent some years exploring one or more of its popular cousins: watercolor, oils and acrylics. In many ways gouache embodies the finer qualities of these media while avoiding many of their limitations.
Gouache resembles watercolor most in its appearance fresh out of the tube and onto the palette. But it is more closely related to oils and acrylics in its behavior in the painting process. Consequently, it is often the artists who have worked successfully with transparent watercolor who have the hardest time making sense of its opaque cousin that is at once so familiar and so alien.
Transparent watercolors work by staining the surface to which they are applied. One gradually builds up glazes of transparent stain, working from light to dark. Highlight areas must be avoided or masked out completely. Gouache, on the other hand, works by creating opaque layers of color that lie atop the surface. Its covering power allows for the layering of lighter tones over darker ones. This quality fosters an approach to painting that is similar to working with other opaque media. However, gouache differs from oils and acrylics in ways that set it apart.
The epic drying time of oil paint precludes its use in most fields of illustration. As with other water-based media, gouache's drying time is almost instantaneous.
The ability to measure its revision time in minutes rather than days, makes gouache a useful tool in the world of overnight assignments and eleventh-hour changes.
While sharing both the opaque quality and convenient dry-time of gouache,acrylics become entirely insoluble and impermeable when dry. Gouache allows the blending of already dried colors by reworking it with a soft, damp brush. In this way one can achieve subtle shading effects or wholesale revisions throughout the painting process. If the demands of the project require an underpainting that is as resilient as an acrylic polymer, acrylic matte medium can be mixed into gouache to meet these ends.
One important key to working well with gouache is mastering the intermixing of water and paint onto the brush. Gouache should not be so diluted that it flows freely like water over the paper. While this is often desirable when working with watercolor, the result here would be a pigment that is not wholly transparent and not nearly opaque. If the paint is not diluted enough, it drags ragged across the surface and leaves a thick layer that is prone to cracking. With a consistency that is like cream, gouache will flow smoothly from the brush and cover surfaces evenly. I find that as I am working an area and the pigment is beginning to dry on my palette, a dip of the brush into water, pigment, and across a dry paper towel results in the desired solution of paint with the added bonus of also being able to repoint my brush all in one move.
When painting one layer on top of another it is important that the first be completely dry. Otherwise, the earlier layer will bleed into the new in an unpredictable and often unaesthetic fashion. Likewise, it is important not to overwork the second layer as this might lift up color unintentionally. A second coat diluted with too much water will have much the same effect. If color bleeding does begin, it is important to stop painting immediately, allowing all areas to dry before proceeding. However, the careful, intentional lifting of colors below can result in beautifully subtle effects. This can be achieved by softly scrubbing the brush, damp with new pigment, into the paint below; but overworking this can quickly turn ugly. Practice and experimentation will develop the control needed to lay down discrete layers when necessary, while allowing the blending of subsequent layers when desired.
There are a number of ways to approach the turning of form and the blending of colors within a gouache painting. Wet-into-wet techniques commonly used with watercolors and oils can be employed with some success. This effect can be quite subtle. However, one is limited to working small areas at a time, as the quick drytime makes the treatment of large areas in this way impractical if not impossible.
When attempting to render areas of shifting value or color, I find that laying down narrow brush strokes of successively graduated tone and/or color yields good results (i.e. these zones of value would resemble a “bulls-eye” around the highlight of a rendered sphere). This effect can be softened by lightly scrubbing the areas with a brush, dampened but not wet. If the increments of value are close enough and the width of each strip narrow enough, it may not be necessary to “soften”the effect, as the viewer's eye will perceive the blending to be complete. This is especially true in illustrations that will be reduced during reproduction.
Crosshatching and stippling can be readily achieved with gouache, again with the option of “softening” the effect or not. When painting an animal that has furor feathers, one can approach the texture as directional hatching, thereby rendering the form and describing detail with the same stroke of the brush. Likewise,when dealing with subjects that have rough or scaly surfaces, the use of stippling can accent those qualities.
Drybrush is also an excellent rendering technique for gouache. Become familiar with the amounts of paint and water needed on the brush. Begin with watered down pigment. After filling the brush with paint, remove the water by brushing across a dry paper towel. A quick stroke across a test sheet before introduction into the illustration is a good precaution. The application of drybrush ranges from lightly feathering to outright scrubbing of the brush into the picture surface. Here, as with the other techniques described, experimentation is the key to understanding the medium.
Another quality of gouache that may be unfamiliar is its tendency to dry at a different value to what it appears when wet. This effect is related to amounts of inert white pigment contained within a given color. Dark colors dry lighter while lighter colors dry darker. I found it useful to develop a series of charts with graduated swatches of dry paint. The charts are of related hues and document the colors' reaction to increasing volumes of intermixed gray, white or other neutral tones. These have been a great help in predicting the results of placing a mixed color into a painting.
DOING IT FOR REPRODUCTION
One important consideration in choosing gouache for an illustration project is the intended method of reproduction. Many newer print shops no longer utilize the traditional method of reproducing color artwork. The graphic arts camera has been replaced by the computerized color scanner as an industry standard. This newer approach requires the artwork to be bent around a large drum in the process. Print shops receiving artwork prepared on heavier boards will often opt to peel the artwork off of its mount. As gouache sits with some thickness on top of a surface, this treatment may result in a painting that is cracked or even destroyed. If the illustration is to be rolled onto a drum, there are some options open to the gouache artist. It may be possible to submit a high fidelity(flexible) print in place of an original. C-Prints,R-Prints, and even high quality color xeroxes may serve the purpose well. Large format transparencies (2 1/4"x 2 1/4" or larger) are preferred by many publishers for large, detailed reproduction of art.If your color art is reproduced at less than half page size, even a well lit, fine–grained 35mm color slide with an industry standard color bar can produce good results.
There are illustration boards that are manufactured with scanning in mind. These "scanner"boards are offered by both Frisk and Crescent. Attached by a low-tack adhesive, the illustration surface of these boards can be easily separated from the heavy-weight backing with a minimum of fuss.Although the abusive peeling process is eliminated, the artwork still will need to be bent around the scanning drum. In this case, avoid large sizes and thickly applied paint. And in all cases, alert the printer to take extra care in handling the artwork.
I prefer working on a hot-press, medium weight illustration board. Crescent and Strathmore both produce these with high rag, acid-free surfaces. Most quality illustration boards and watercolor papers may be used with gouache, but beware of boards that are not acid-free as these may self-destruct over time. Hot and medium press surfaces are best, with cold press surfaces often being too textured to suit finely detailed gouache paintings. As with other water-based media, the surface must be rigid enough so as not to warp and buckle under the many applications of water. Thinner boards and papers must be taped to a board, such as masonite, if they are to remain flat.
Many watercolor brushes will be suitable for working in gouache. Gouache does tend to be harder on brushes than watercolors, and so I've filled out my collection with brushes from various inexpensive lines. Winsor-Newton Sceptre, Atrium Aquarelle, and Grumbacher 178 are all sable or sable/synthetic blend brushes whose spring and durability make them good choices for pushing gouache around. I often use a 1/2 inch or 1 inch flats to lay in broad areas.However, I always use the more expensive Kolinsky sable rounds such as Winsor-Newton Series 7 for painting smaller details. I have a set ranging from 000 to 1that has seen many miles of use. A toothbrush can be used to produce interesting speckled effects by flicking your thumb across its paint-filled bristles (careful where you aim that!). Sponges also can be used for textural effects.
Various watercolor palettes can be adapted for handling gouache. A number of white plastic palettes on the market have small cups that seem just the right size to contain sundry mixes of gouache colors. I find these great for laying out a sequence of graduated values side by side. I own a number of the smaller six-cup versions to which I dedicate one color per set. These are laid out around the drawing table and give me the option to reach out and pick up an entire color family if needed. The large metal butcher's trays are also fine for laying out a spread of colors.In whatever palette you choose, it is useful to have low barriers around its edges. Squeezing the brush against these sides will enable you to drain off excess paint and water. A dampened paper towel can be placed on top of your mixed colors to retard their drying time between sessions. If large, even areas of paint are required, mix extra paint and store the extra in sealed plastic 35mm film canisters.This keeps the gouache fresh and is essential when reworking or repairing these areas. And when gouache does dry out on the palette, don't clean it off until after the illustration is finished (and O.K.'d by the client). Dried lumps of paint can be brought back to life by some scrubbing with a dampened brush. Although not effective for the coverage of large areas, these resurrected colors are great for repairing and reworking various details in the illustration. It is not uncommon to discover the richest mixtures of color within such dried cakes. They can be wonderful choices to reintroduce into the latter stages of a project. Reflected light and warm or cool complements all can be mined from your palette and will serve to unify the illustration.
With an extensive selection of colors on the market today, there is room for great subtlety when choosing tubes of paint for a project. Winsor-Newton, Talens, and Linel all make gouache of good quality, with Winsor-Newton offering the widest palette and widest distribution. Colors of the same name made by various manufacturers often are very different hues, expanding further the palette available on the market. This selection includes an excellent range of grays from Winsor-Newton in cool, neutral and warm with five grades of darkness each. Talens produces a series of neutral grays that are in fact quite cool and complement the selection from Britain. Linel offers a small but useful selection of grays as well. Marabu and Grumbacher produce pan sets of grays that are used primarily for photo-retouch. While not effective for large coverage, these pan sets are good for detailing.
When choosing tubes of color for a project, one must decide whether the finished illustrations need survive unaltered far beyond the moment when the pieces are photographed for reproduction. Although there is a palette of over one hundred and twenty colors on the market, approximately one third of these are fugitive, meaning that the dyes have a propensity to fade (sometimes radically)over time. Most major manufacturers of pigment include a permanency rating somewhere on each tube of paint. Often there is additional technical information encoded on the tube that can be of great use to the artist wishing to fully understand the properties of the medium employed. Opacity and staining power are two qualities of gouache that can strongly impact the results of an illustration;the former indicates the ability of a color to cover and hide elements of the painting below it, the latter denotes the strength of the dyes used and reveals their ability to bleed through colors placed on top of them. When attempting to fully cover one layer of paint with another, the use of a low opacity pigment over one of high staining power will not be successful, resulting in unpredictable coverage that may change over time.
Since gouache is a water-based medium, one need not be concerned with toxic fumes and solvents. However, as with most other media where there is a wide palette of colors, certain pigments are derived from material that may provide a health hazard. This is especially true of many of the cadmium and cobalt hues. Hazards can be minimized by following appropriate precautions. Users of water-based paints should avoid the all-too-common habit of repointing a brush by wetting it with one's lips (users of oil based paints probably don't need to be told this).Airbrush artists should be especially aware of properties of the colors they choose,as airborne particles can be both inhaled and ingested. Masks and ventilation hoods can reduce this problem, but as manufacturers have widened their selection to include safe “imitation” variants of the offending colors, avoiding the more toxic materials seems the way to go. Some manufacturers encode this information on their labels. All manufacturers develop technical data sheets that include pertinent details of every tube in their product line. Often these can be gotten through local retailers or by contacting the companies directly.
THE PROCESS UNFOLDS
In designing a gouache illustration, I plan ahead for how I will develop the large flat shapes that will serve as an underpainting. Once I decide on my treatment of the various elements within a scene, I lay a sheet of tracing paper over my preliminary drawing and begin outlining around these shapes or zones. This tracing then becomes the first of many stages in the process of transferring information from drawing to board. The first stage usually is confined to basic silhouettes of objects, or groups of objects that will share a common underpainting. These areas will be painted as flat areas of color and allowed to dry.
Sometimes I plan to paint the entire board a single unifying color over which I'll introduce the various middle ground and foreground elements. This is especially effective when dealing with subjects that are to contain common colors throughout, such as forest and underwater scenes as well as any scenes with atmospheric lighting. Thus I save the time it would take to paint the background carefully around each and every element. And in the cases where a flat and even tone is desired, such as in a sky, this allows me to work quickly so as to achieve the result effectively. Although one can eliminate this step by working on colored papers, these are not lightfast and should be avoided if archival qualities are a consideration.
With the underpainting(s) in place, I proceed by transferring additional outlines and details directly from my preliminary drawing onto these flat shapes. I generally transfer my drawings from tracing paper by coating its reverse side with graphite dust, or when transferring onto a darker underpainting, white chalk. Using some pressure I then draw directly onto my tissue overlay with a sharpened pencil, being careful not to cut the tracing paper and contact the painting below. Occasionally I will take advantage of an aspect of opaque media that allows for a more direct and less messy transfer technique. Since the gouache paint sits on the board with some thickness, the point of the pencil can be used to lightly score the outline through the tracing paper into the paint, reducing (or eliminating) the need for much graphite/chalk on the back of the preliminary drawing. With light held low to the surface of the illustration, the raking light will reveal the transferred information, which can be reinforced by outlining with a hard-leaded pencil. Be sure to carefully erase any excess graphite from the surface of the painting with a kneaded eraser, as the next layer of gouache will pick up these impurities and muddy the lighter colors.
I tend to avoid transferring the smallest details and textures unless they are diagnostic to the subject. This saves time and confusion. Instead I transfer the major plane changes, cast shadows, indications of fur direction, and general details that would stand out at arm's length. After these are successfully transferred and reinforced with a graphite pencil, I freehand the smaller details or wait for the later stages of painting to introduce them with my brush. This reduces the redundancy that often is built into the illustration process.
As the painting progresses, I make good use of the underpainting already completed. These flat areas are usually middle tones of the local color, over which now sits penciled information transferred from my sketch. Working out from the middle tone, I extend the range of shadows and highlights which helps to quickly establish a good sense of form in space. Whenever possible, it is best to develop the whole painting in this way before diving into individual areas of fine details. Likewise, I find it useful to introduce the darkest dark at this stage. These practices assist in creating an illustration that is uniform in treatment, with the darkest areas helping to push the tonal relationships to their fullest potential. In some cases this approach is not practical. If a landscape is to include extremely intricate foreground elements, the choice might be to render the back/middle ground elements to a high or even finished degree. The excellent covering power of gouache allows one to drop entire foreground subjects into a completely rendered scene. And while this approach is not always desirable, there may be times where ornate foreground figures or an intricate series of middle/background levels will suggest this option.
However, one must be very aware of the limitations built into such choices. It is all too easy to complete entire sections of a painting, only to later find the tonal range far too pale next to that of a newly introduced element. Swatches of the darkest colors, painted to the edge of a small board and let dry, will reduce the chances of such surprises. By moving this board across regions of the illustration one can get a good sense of the tonal relationships that are being established.
A TOUCH OF GRAY
When creating the illusion of depth within an illustration, I take advantage of the large series of grays available on the market. I found these grays to be invaluable in their ability to mute the vibrant colors that squeeze fresh from the tube. The neutral quality of the gray greatly reduces the “chalkiness” associated with the lightening of a color by intermixing white. Darkening a color by adding black often results in a color that becomes too dark long before the black serves to mute its vibrancy. These qualities can be more carefully balanced when intermixing a dark gray instead.
To approximate more closely the colors found in nature, I find that I am intermixing anywhere from 50% to 90% gray into my palette. This high proportion, combined with the premixed series of values in warm and cool grays suggests a powerful option when establishing spatial relationships within a scene. This premixed sequence allows me to create “zones” of contrast that recede in value, establishing aerial perspective within a scene. The values of a color can be shifted predictably by interchanging the gray used in the mixture. For example, the base color of a foreground black spruce might be achieved with a mixture of 20% Viridian Lake, 20% Forest Green, and 60% Cool Gray #4. A middle ground spruce would retain the same proportion of colors, with the only difference being in the use of Cool Gray #3 in place of #4. This produces the visual effect of two trees of the same hue sitting at varying depths within the picture, as suggested by the relative shift in value. The five main values of gray (with #1 being the lightest and #5 the darkest) are a starting point from which an infinite field of grays can be premixed. The introduction of small amounts of Cerulean Blue into these mixes can be used to emulate the high presence of ultraviolet light scattered about on a sunny day. Dawn and dusk would suggest the inclusion of warmer tones.
I came upon this approach quite by accident, and am continuing to experiment along the way. Certainly any opportunity to reduce the variables within the illustration process can create departure points from which complex and successful illustrations will grow.
By learning to design with larger shapes one can impart a graphic quality to the illustration that may become masked but never completely hidden by subsequent levels of detail. This graphic quality can serve to draw the viewer in from afar, allowing the artist to then delight and inform the viewer with the texture, nuance, and subtlety that a gouache rendering can readily achieve.
Cleary, Shirley. “The Opaque Power of Gouache,” The Artist's Magazine, 1986, September issue.
Hodge, Gerald P. “Gouache (Opaque Watercolor)” in The Guild Handbook of Scientific Illustration. Van Nostrand Reinhold, 1989.
Hodges, Elaine, R. S. “Transferring Drawings,” Journal of Natural Science Illustration, Vol. 1(3), 1991.
Mueller, Ned. “Getting results with Gouache,” The Artist's Magazine, October 1989.
Tennant, Daniel K. “Developing Detailed Pictures with Gouache,” American Artist, September 1986.
Fig. 01 - Detail of Gray Day, © Frank Ippolito, 1989
Transparent watercolors can be used within a gouache painting. However, if the piece is to be photographed, be aware that areas of watercolor generally will reproduce paler than they appear in the original. This effect is due to the primary difference between transparent and opaque media. Watercolor derives its luminosity from light reflected off the surface of the paper, which passes through the transparent glazes of paint. Opaque media reflects the light directly off the surface of the paint. In photography these two subjects have greatly different exposure/lighting requirements. The fish was painted in transparent medium in an attempt to take advantage of this fact. Any washing out of the fish would only serve to reinforce its reflective nature.
Fig. 02 - Detail from NYC Falcons, © Frank Ippolito, 1995
The background for this poster was airbrushed in first using Turner's acryl-gouache. All detail and highlights were added afterward. This allowed an even gradation that unified the picture and added atmosphere.
Fig. 03 - Forest Jewel, © Frank Ippolito, 1992
Based on a beautiful photo reference by Stephen Dalton, this painting was rendered over the course of two separate technique demonstrations.First the board was painted green, corner to corner, except for a red circle–in the position of the eye. It was the eye that was fully rendered during a short GNSI workshop demo. Six months later I once again attempted to fully render a selected area. This time as a demo for my illustration class, I attempted to finish the amphibian. Here I ran into trouble, and struggled for a couple of hours as my students looked on.Finally defeated, I sent them home. But I stayed around and fussed with the piece awhile.Out from under their watchful eyes, I proceeded at a more leisurely pace. I decided to work into the background to use up some of the paintI had mixed. As I began to fill in the dark areas between the leaves, I watched as the entire piece came together. I had been ignoring my own advice and had focused on small areas rather than developing the entire picture together. Once I returned to my usual approach, the painting was resolved over the course of an evening.It was interesting to watch the expressions on the faces of the students when they returned the following week and saw the finished piece. Each of them remarked on how important it was for them to seethe struggle in the process. The lesson they learned went beyond the basic understanding of technique. It would give them the confidence to continue on through difficult stretches of work, rather than give up.With gouache it is always possible to rework areas that have been worked to death.For me the lesson was simpler: it is generally good practice to heed one's own advice.
Fig. 04 - Van Cortlandt Park, © Frank Ippolito, 1991
The two stages of this illustration reveal extensive use of flat areas of color beneath the intricate details of the finish. The cattails in the left hand foreground are good examples of middle-value underpaintings, onto which are introduced high-light and shadow. As the background willow tree was to be a dominant compositional element, I chose to underpaint it with its darkest value–likewise the water and the face of the great white egret. The red-winged blackbird is to contain this painting's darkest value, and this is already established during the earliest stages of the project.
Fig. 05 - Green Heron, © Frank Ippolito, 1990
This scene takes advantage of the use of premixed grays to establish aerial perspective. The rules of aerial perspective dictate that an object farther from the viewer be of a lower contrast, hence a lighter value, than a similar object seen in the fore-ground. This convention is easily perceived in nature when viewing a mountaintop from a distant vantage point on a hazy afternoon. Details of nearby elements such as rocks or trees appear in sharp contrast and a full tonal range, while such details of the distant peak will seem much softer and of a lighter value. Any intervening elements will appear in a graduated sequence, receding from the full tonal range of the foreground to the lighter values of the background. Landscape artists have long made use of this phenomena to create the illusion of depth within a scene. Scientific Illustrators have adapted this convention, artificially imposing this distortion perceived in a field-of-view miles deep onto specimens as small as a few millimeters across. Rendered as if in a sea of fog, details on the far side of the specimen appear lighter than those on the nearest plane. This allows the illustrator to overcome the limitations of a given medium,expanding the amount of information conveyed.
Fig. 06(A-E) - Tyrannosaurus, © Frank Ippolito, 1993
A sequence of five stages of this gouache study bears witness to the ongoing process of rendering a detailed subject. Shown slightly smaller than actual size, this board first was painted over with a few coats of Warm Gray #3 and allowed to dry.The neutral background enabled me to later introduce highlights that would seem to lift the image off the page. Using this color fresh out of the tube also afforded me a virtual eraser by allowing me to eliminate details and return to ground with the simple re-introduction of the premixed gray. The drawing was then transferred onto the gray board via carbon-backed tracing paper. Some of the lines still can be seen throughout the early stages of work. In this case I chose not to reinforce the fuzzy carbon lines with a sharper graphite drawing since the smaller drawing area reduced the chances of smudging the carbon. The forgiving nature of gouache makes this less crucial as you are able to “draw” new detail over the old with a fine paintbrush. The grayscale images A-D allow you to see the tonal progression, though colorGouache was used in all stages on a gray background.
Fig. 07 - Protoavis, © Frank Ippolito, 1992
The ornate feather pattern of this extinct bird suggested a unique approach in developing this illustration. Virtually the entire painting was rendered corner to corner before the bird was introduced. I transferred its outline using colored chalk on the back of my tracing paper. After the bird was fully painted, I airbrushed in the shafts of light. Finally the various points illuminated by the shafts were highlighted.
Fig. 08 - Acorns, © Frank Ippolito 1991
ABOUT THE AUTHOR
Frank Ippolito studied Communication Design at Pratt Institute, and has served as Senior Artist on the staff of the American Museum of Natural History since 1983. In addition, he currently teaches Scientific Illustration and drawing at Fairleigh Dickinson University. Frank joined the GNSI in 1986 and has been actively involved giving talksand workshops at national GNSI conferences.