Watercolor, gouache, and poster color paints have a lot of similarities, but they’re not exactly the same. Watch the video below and keep reading for a detailed look at the differences between these versatile water-soluble paints.
Watercolor is transparent and gouache is not. Otherwise, they’re pretty similar! We’ll sum up the differences here and get into detail below.
Watercolor | Gouache |
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Watercolors, gouache, and poster colors all rely on pigments for their coloring rather than dyes. This means that tiny pieces of colored stone or other physical materials are suspended in the paint mixture, rather than being dissolved like dye.
The most consistent difference between these paints is the size of their pigment particles. Western-style watercolor pigment particles are the smallest, gansai watercolor particles are slightly larger, gouache particles are bigger yet, and poster colors have the biggest particles.
Generally speaking, small pigment particles make paint that is more transparent and harder to lift from the paper. They are also less likely to form granulation effects. This is because the lightweight pigments spread more evenly over the paper. Bigger, heavier pigments tend to settle into the texture of the paper and may have visible darker spots or “grains” of color.
Some pigments contain toxic chemicals like cadmium and cobalt. However, in the paint-making process, these chemicals are coated in binder, rendering them insoluble in water. This greatly limits health risks. That said, they are still fat-soluble, so don't eat them! To be extra careful, you can also let paint water fully evaporate, then dispose of it into a trash can, instead of pouring it back down the pipes.
All paint uses a binder to hold the ingredients of the paint together. Many watercolors, gouache, and some poster colors use the dried sap of the acacia tree, known as gum arabic, as their binder. Gum arabic easily redissolves in water after it has dried, so it’s easy to reactivate paint made with it for blending and lifting.
Japanese gansai watercolors traditionally use animal glue as a binder, but many modern gansai paints use alternatives like beeswax and sugar. These binders can give gansai a glossier finish than Western watercolors, but they otherwise behave quite similarly.
Water-soluble paints also contain additives, which vary considerably between product lines and even between individual paints in the same line. Some common additives are humectants to keep the paint moist, preservatives to prevent mold, brighteners to make the paint more vibrant, and dispersants to help the pigment spread out in water.
Other additives “stretch” the paint so that it contains less pigment. This can make the paints less expensive or tone down intense pigments so that they are easier to use with other paints in the same product line.
Although some additives are necessary, they can have side effects. Paints with brighteners look more colorful in the pan and when wet, but they are typically more opaque and develop a faded or chalky appearance when dry. Paints with dispersants or large amounts of humectants can penetrate more deeply into the paper fibers and resist lifting. Not all manufacturers list what additives they use, but artist quality paints usually have more pigment relative to additives than student grade paints.
Be sure to test paints on a piece of scratch paper to see how well they blend if you’re not sure whether they’re made with single pigments or not. If they don’t blend well, use thicker layers of paint to reduce the chances of the underlying color reactivating and blending with the new color.
Another factor to keep in mind is color temperature: a “cold” or bluish yellow might be a pure pigment, but when mixed with red, it won’t make the vibrant orange that a “warm” yellow would. For a little more information on color mixing, check our guide to The Best Watercolor Supplies.
Paints made with smaller pigments, like watercolors, tend to be harder to lift because the particles can nestle snugly between paper fibers. Larger particles don’t fit between paper fibers as well, so they are more likely to sit on the surface of the paper, making lifting easier.
Watercolor paint is known for its transparency, which allows it to create delicate washes and nuanced, layered shading. Its transparency comes from the size of its finely ground pigments. The small particles spread evenly over the paper to make smooth washes and allow the color of the surface below to show between each particle.
Although the transparency of watercolor can result in beautifully luminous artwork, it also limits how these paints can be used. Light colors are not opaque enough to cover previous layers, so they must be applied before dark colors and then carefully avoided for the rest of the painting.
You may be able to lighten dark areas with lifting if you accidentally put down a dark color too early, but no guarantees! You can also cover areas that need to stay light with masking fluid to protect them from stray paint.
Be aware that watercolor tends to dry lighter than it looks when wet on the page. We recommend creating a swatch sheet of all of your paints, so you have visual references for how they dry. If you’re painting quickly, don’t be afraid to put down bold, bright colors.
Some watercolors are less transparent than others. Certain pigments, especially earth minerals like cadmium red and yellow ochre, naturally make more opaque paints. Other paints are made more opaque with additives. Both these and gouache are sometimes referred to as opaque watercolors, but gouache is made with larger pigments.
Gansai are traditional Japanese watercolors. They are designed to be used in a single layer on absorbent washi paper rather than in multiple layers, but they can still be used that way. They are made with larger pigments than Western watercolors. This makes them both more opaque and easier to lift, as the larger pigments block more of the paper and don’t penetrate as far into the surface. They also tend to be made with more intense pigments for extra vibrancy. When used for washes, they often create interesting granulation effects with a textured or mottled look.
Gansai are not usually bound with gum arabic. The traditional binder is animal glue, but these days gansai can be made with beeswax, sugar, and other binders. This can give gansai a glossier finish than Western watercolors, especially in areas where they were applied heavily. Kuretake Gansai Tambi Watercolors are made with water-soluble resin. You can see swatches of the Kuretake Gansai Tambi paints in this video.
Gouache, pronounced goo-aash or gwash, is very similar to watercolor paint in its composition. However, it is designed to be opaque and to dry to a flat finish. It is made with intense concentrations of large pigments. Many gouaches use additives like chalk and titanium dioxide (known as titanium white when it is made into a paint) to make them more opaque. Others, like M. Graham Artists’ Gouache, do not. Avoiding additives means that some colors remain semi-transparent, but it also keeps them more pure. This allows artists to choose whether to mix colors with titanium white to achieve full opacity or work with them as is.
Gouache’s opacity gives you more freedom to paint on colored papers and add light colors over darker hues. Its flat finish makes it good for solid shapes that don’t show the pooling and gradation common to watercolors. Gouache can be diluted like watercolor paint if you don’t need its full opacity, but its washes aren’t quite as delicate. Gouache also lifts easily due to its larger pigments. If underlying colors reactivate and mix with layers you add over them, layer with thicker paint to reduce the chance of accidental lifting.
Unlike watercolor, light-colored gouache dries darker and dark gouache shades dry lighter. If you come to gouache from watercolor, the colors that dry darker will be much more noticeable and can even be frustrating. This behavior varies between brands. Be sure to mix a lot of paint if you need to cover a large area in a flat color, and be sure to keep practicing; as you learn the paint’s behavior, adjusting for it will become second nature.
In addition to being used on its own, gouache is easy to use with watercolor paints. You can use it to add light-colored highlights over dark paint (though it has a more solid feel than the delicacy of negative space in watercolor) or even mix white gouache with watercolor paint to make the watercolor more opaque and vibrant.
Though JetPens does not offer them, acryla gouache paints are a large part of the gouache market. Acryla gouache is not a water-based paint. Like its name implies, it is made with an acrylic binder. It cannot be reactivated by water (whether on the page or in an accidentally dried-out tube) and will not allow you to layer watercolors over it. If you see “acryla” on a tube, keep in mind it will behave quite differently than traditional gouache.
Unlike watercolor and gouache, poster color does not refer to a specific kind of paint. Instead, it is a general term for opaque water-soluble paints meant for scanning and reproduction rather than display. Poster colors are usually less expensive than paints intended for display, and not very lightfast. Their opacity comes from additives and coarsely-ground pigments. They also lift very easily. It’s a good idea to test any new paint so you know how it will behave before you use it in your art, but we especially recommend testing poster colors because they can be made with a wide variety of different binders.
Poster colors are highly opaque. Like gouache, they work well on both white and toned paper. You can easily add light colors over dark hues, so they are wonderfully straightforward to paint with. They are also very vibrant. Some colors are made with multiple pigments and can form muddy hues when mixed, so it’s best to start with large blocks of thin color and add details on top with thicker paint. This prevents the previous layers from reactivating and mixing with the new paint. Stick to just a few layers to reduce the chance of the layers blending, as demonstrated in our Nicker Poster Colours video.
Nicker Poster Colours are known for their use by Studio Ghibli and other Japanese animation studios, who use them to paint backgrounds. They’re different from typical poster colors in that they are made with gum arabic, like most gouache and watercolor. Nicker also lists the paints’ lightfastness, opacity, pigment codes, and tendency to bleed into colors layered over them, so you can select only the colors with the properties you need.
We tested representatives from each paint category to see how they compared in terms of transparency, blending, lifting, layering, and when thinned to a wash. Bear in mind that these are only broad comparisons. In addition to varying by paint type, all of these characteristics vary considerably between brands, product lines, and even different colors within the same product line.
Paints also behave differently on different paper. We performed our tests on Global Art Fluid Watercolor Paper and used similar colors across these tests to keep them as comparable as possible. You can see the product lines and colors used for each test below.
Paint Type | Product Line | Blue | Green | Yellow |
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Standard Watercolor | Holbein Artists' Watercolors | Phthalo Blue (Yellow Shade | Hooker’s Green | Lemon Yellow |
Gansai Watercolor | Kuretake Gansai Tambi Watercolors | Cerulean Blue (No. 63) | Hooker’s Green (No. 52) | Lemon Yellow (No. 40) |
Gouache | M. Graham Artists' Gouache Tubes | Phthalocyanine Blue (Primary) | Hooker's Green | Azo Yellow (Spectrum) |
Poster Color | Nicker Poster Colours | French Blue (125) | Chrome Green (2) (36) | Lemon Yellow (27) |
This test demonstrates how each paint looks when used at full opacity and when thinned to a wash, with nothing else beneath it. Washes should be almost as thin and translucent as glass, so they work best with paints made with small pigment particles. This allows them to spread evenly and maximize their transparency.
Washes can be made with more opaque paints like gouache, especially if they are made without opacifying additives, but the effect is less delicate. The larger pigment particles can look grainy when thinned out. Poster colors are less suitable for washes because they are more likely to get muddy when other colors are layered over them.
Artists often want watercolor paints to be as transparent as possible to give their work a luminous quality. At the same time, they generally prefer gouache and poster colors to be as opaque as possible so they can cover underlying layers and add light-colored elements when it’s most convenient. We tested for transparency and opacity by drawing gradient swatches over a heavy black line drawn with a Sakura Pigma Micron Pen. The more the paint covers the line, the more opaque it is.
When using any of these paints, artists frequently add more paint on top of previous layers to build shadows, dimension, and add details. Watercolor layers are thin and translucent, so artists must start with light colors and gradually build to darker hues. Gansai watercolors are traditionally used in a single layer but can support watercolor layering techniques.
Because gouache and poster colors are more opaque, artists have more flexibility to layer light colors over dark. When using poster colors, it’s best to minimize the number of layers to prevent them from getting muddy. The following tests illustrate how each paint performs when light, medium, and dark hues are layered over each other.
One of the advantages of water-soluble paints is that you can reactivate the color with water and “lift” it from the paper if you want to lighten an area that has too much paint on it. This is usually easier with paints that have larger pigments, as smaller pigments can get stuck between paper fibers. We lifted a stripe in the middle of each swatch by wetting it and blotting it in order to see how easy each paint was to lighten.
All of these paints are easy to mix in a palette or on the paper, but colors made with only one pigment usually blend more predictably. Colors made with a mix of different pigments may produce muddy hues when blended together.
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Watercolors, gouache, and poster colors have a lot of similarities, but each has its own unique character. Which paint is your favorite? Let us know in the comments below!
Product | Transparency | Surface | Add to Cart | |
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Coliro Pearl Watercolors | Transparent to semi-transparent | Watercolor paper, colored paper | Add Items to Cart | |
Holbein Artists' Watercolors | Transparent to semi-transparent | Watercolor paper | Add Items to Cart | |
Sakura Watercolors | Transparent to semi-transparent | Watercolor paper | Add Items to Cart | |
Yasutomo Watercolors | Transparent to semi-transparent | Watercolor paper | Add Items to Cart | |
Akashiya Gansai Watercolors | Semi-transparent | Watercolor paper, washi paper | Add Items to Cart | |
Boku-Undo Watercolors | Semi-transparent | Watercolor paper, washi paper | Add Items to Cart | |
Kuretake Gansai Tambi Watercolors | Semi-transparent | Watercolor paper, washi paper | Add Items to Cart | |
M. Graham Artists' Gouache Tubes | Opaque to semi-transparent | Watercolor paper, colored paper | Add Items to Cart | |
Nicker Poster Colours | Opaque | Watercolor paper, colored paper | Add Items to Cart |