Watercolor Mediums: What They Are and How to Use Them

Granulation Medium

Granulation is the effect where pigment particles settle unevenly into the paper surface as paint dries, creating a speckled, grainy texture.

Some watercolor pigments do this naturally. Granulation medium lets you trigger the same effect with any color, including those that dry completely smooth on their own.

How the Effect Works

Natural granulation vs. medium-induced: heavier, irregular pigment particles sink into the paper’s texture instead of spreading flat. When those particles are not present in the paint, granulation medium introduces the conditions that encourage settling anyway.

Rough and cold press paper produce the strongest results. On smooth hot press, granulation is more subtle because the surface offers fewer low points for particles to collect in.

Daniel Smith’s range of mineral-based PrimaTek pigments are well known for natural granulation. Pigments like Cerulean Blue, Raw Umber, and Ultramarine have larger, more irregular particle sizes that granulate without any medium at all.

When to Use It

Best for subjects where texture carries the image:

• Rock faces and stone walls
• Aged wood and bark
• Overcast or atmospheric skies
• Beach and sand foregrounds

Adding granulation medium to an already-granulating pigment amplifies the effect, which can go too far. Test on scrap first.

Application method matters. The strongest results come from dropping medium into wet paint already on the paper, not mixing the two together beforehand. According to Vandy Massey Studio, this technique produces a more concentrated textural effect than pre-mixing.

Brands and Practical Notes

Winsor and Newton, Schmincke, and Daniel Smith all produce granulation medium. Winsor and Newton recommends their Cotman paper range as especially suited for granulating techniques.

Be generous with quantities. Small amounts produce subtle results; a proper granulating effect takes a visible dash of medium in a reasonably concentrated mix.

One limitation: granulation medium is not useful for portrait or smooth-finish work. The texture is deliberate and noticeable. Using it where you want clean, even washes will work against you.

Texture Mediums and Pastes

Texture mediums add physical surface variation to watercolor work. Unlike granulation medium, which works through pigment settling, these products introduce actual particles into or under the paint layer.

Winsor and Newton describe their Texture Medium as containing fine particles that create a rough-looking surface when applied directly to paper or mixed into the paint itself. It can be layered, and subsequent washes settle differently over textured areas than they do over flat paper.

Pumice Gel in Watercolor Work

Pumice gel is primarily an acrylic product from Golden, but artists use it under watercolor to create an absorbent, coarse ground. Applied over gessoed canvas or wood, then allowed to cure, it accepts watercolor washes the way rough paper would.

Artists Network notes that pumice gel can be mixed with soft gel to control both transparency and absorbency level. More gel means more transparent and less porous. Straight pumice gives maximum texture and maximum absorption.

Drying color: pumice gel dries with a grayish tone because of the volcanic rock content. That affects the apparent value of any paint applied over it. Worth testing before committing to a light-key painting on pumice-prepared board.

Fiber Paste and Paper-Like Surfaces

Liquitex fiber paste contains cellulose fibers that create a surface resembling watercolor paper when applied to rigid supports.

It is particularly useful for mixed media work, where an artist wants [mixed media] surface behavior on a board or canvas. The paint lifts, blooms, and flows in the way it would on paper, not like it would on a sealed acrylic surface.

Applied in thin coats: keeps the fiber texture even and workable. Thick applications crack. The same patience required for watercolor ground applies here.

Retarders and Drying Time Mediums

Watercolor dries fast. In warm or dry climates, it can be unworkably fast.

A wash that needs 30 seconds of blending can lock up in 10. Retarders buy back that working time.

What Retarders Actually Do

Retarders slow evaporation from the paint film. This keeps the paint workable for longer, giving more time to blend gradients, soften edges, and rework areas before the paint sets.

Hard limit: retarder should not exceed 15% of the total mixture, according to Golden Artist Colors. Beyond that threshold, the paint film may never fully dry and will remain sticky indefinitely. That is not a problem you can fix after the fact.

Retarders designed for acrylic paint are not the same as those made for watercolor. Acrylic retarders work by modifying the polymer film formation. Watercolor retarders, like glycerine-based formulas, work with the water-soluble binder in a different way. Using the wrong one can affect paint adhesion and surface solubility.

When Retarders Help vs. When to Skip Them

Use retarder when:

• Painting large, blended washes in warm or dry conditions
• Working on wet-on-wet backgrounds that need extended blending time
• Painting in direct sun or with a fan running nearby

Skip retarder when: you are layering multiple washes. Slowed drying time means longer waits between layers, and if the first layer is not fully dry before the next goes on, lifting and color contamination follow.

Honey is a traditional, low-tech alternative that some artists still add in very small quantities to their watercolor. It extends working time and adds slight gloss. Several professional-grade paints already contain it as a humectant. M. Graham is known for using honey in their watercolor formula as a working property modifier.

Iridescent and Interference Mediums

These mediums add optical effects that flat pigment cannot produce. They catch and reflect light rather than simply absorbing or reflecting a fixed color wavelength.

Iridescent Medium

Iridescent medium contains pearlescent particles that add a metallic sheen to any watercolor it is mixed with.

Winsor and Newton describe theirs as particularly effective when mixed with transparent colors, especially over dark backgrounds, where the shimmer is most visible. Mixed into a mid-tone blue or green on white paper, the effect is subtle. The same mix over a deep wash turns noticeably luminous.

Two application approaches:

• Mix directly into paint for an overall shimmer throughout the wash
• Apply over a fully dried layer as a glaze for a surface shimmer effect

Da Vinci’s iridescent medium works in both wet-on-wet and dry surface applications. The wet-on-wet approach gives a more diffuse, atmospheric shimmer. The dry application gives a more defined surface glow.

Interference Medium

Interference colors shift depending on the viewing angle. The color you see straight-on differs from the color visible at an oblique angle.

Golden’s QoR line introduced eight iridescent and interference watercolors in 2024. The mica particles responsible for the effect reflect light so completely that standard spectrophotometer readings cannot accurately measure them, according to Golden Artist Colors’ own lightfast testing documentation. The reflectivity causes the dry paint to act like a mirror against the sensor.

Thinner applications work better. Golden notes that thick interference layers cloud the paint and reduce the shift effect. Thin washes force the mica particles to lay flat, maximizing the surface area exposed to the viewer and intensifying the shimmer. Mixing with matte materials kills the effect entirely.

These mediums suit decorative, botanical, and fantasy illustration work. Painters working in abstract styles use them to create surface interest without relying on color contrast alone. Less useful for realism or landscape work where optical accuracy matters more than surface effect.

How to Choose the Right Watercolor Medium

Start with the problem, not the product.

Every medium solves something specific. Buying a full set and experimenting with all of them at once is a fast way to waste both paint and paper without learning much. Pick the one medium that addresses your current limitation and test it thoroughly before adding another.

Match Medium to Problem

Student Grade vs. Professional Grade Mediums

Student-grade mediums typically contain more filler and less active ingredient. The granulation effect is weaker. The gum arabic concentration is lower. The results are inconsistent.

The fine art watercolor paints market was valued at USD 3.67 billion in 2024, according to Proficient Market Insights. That reflects a market where professional-grade materials are widely purchased. But mediums specifically are an area where professional quality pays off in a way that is immediately obvious, because the effect either happens or it does not.

For mediums, buy professional grade from the start. The cost difference between student and professional masking fluid or granulation medium is small. The difference in behavior is not.

Compatibility and Mixing Risks

Mediums from different manufacturers are generally compatible with the same brand’s watercolor paint. Cross-brand mixing is less predictable.

Mixing multiple mediums in the same wash causes the most problems. Gum arabic plus retarder in the same mix, for example, creates an unpredictably slow-drying, overly glossy layer that is tricky to work over. Use one medium at a time until you understand how each behaves on its own.

The same approach applies whether you are working in impressionist-style loose washes, tight botanical illustration, or en plein air painting in variable conditions. The medium should serve the painting, not complicate the process. Keep it simple, test on scrap, and add one variable at a time.

Understanding the full range of painting mediums across different media also helps here. Watercolor mediums exist on a spectrum alongside oil and acrylic mediums. Many of the underlying principles, controlling working time, adjusting viscosity, introducing texture, carry across all of them.

What Are Watercolor Mediums

A watercolor medium is any substance added to watercolor paint or water to change how the paint behaves on a surface.

That sounds simple. But the range of what falls under that definition is pretty wide, covering everything from natural plant gums to latex-based resists to mineral-particle pastes. Understanding them as a category first makes choosing the right one much easier.

Key distinction to get right from the start: mediums are not the same as the paint itself, the paper, or the brushes. They sit between those elements and the final result. You add them to alter a specific property, not to change what watercolor painting fundamentally is.

The global watercolor market was valued at USD 3.143 billion in 2024 and is projected to reach USD 5.558 billion by 2035, according to Market Research Future. That growth is partly driven by artists pushing the medium beyond its traditional limits, which is exactly where mediums and additives come in.

The properties artists most commonly want to change:

• Drying time (slower for wet blending, faster for layering)
• Paint transparency and gloss
• Flow and surface tension
• Physical texture on the paper surface
• Which areas of the paper accept paint at all

Water alone handles none of these with precision. Mediums do.

Mediums vs. Paint vs. Tools

The confusion usually starts at the supply store. Everything gets shelved together, and the labels are not always obvious.

Paint contains pigment, a binder (almost always gum arabic), and water. That is the base. Mediums change how that base behaves. Tools (brushes, palettes, paper) determine how the paint is applied and absorbed.

Mixing up these categories leads to mistakes. Adding what you think is a medium directly to your paint when it is actually a varnish or fixative (meant for finished, dry work) can permanently alter your painting in ways you did not plan for. The distinction is worth memorizing early.

Why Mediums Matter More Than Most Beginners Expect

Most people start with just water and paint. That works. But it leaves a lot of control on the table.

Experienced watercolor artists treat mediums as precision tools. A drop of ox gall in your water changes how paint spreads on difficult paper. A small amount of gum arabic in your mix slows drying time just enough to keep a gradient workable. None of that is possible with water alone.

The painter J.M.W. Turner, known for his atmospheric washes and luminous skies, was documented using gum arabic to increase the gloss and depth of his watercolor glazes. That level of surface quality does not come from paint and water alone.

Watercolor Mediums vs. Additives vs. Varnishes

Three categories. Very different roles. Frequently confused.

The practical reason this matters: applying a varnish before the paint is completely dry traps moisture and clouds the surface. Applying a flow additive like ox gall to finished layers lifts color you meant to keep. Wrong category, wrong timing, ruined result.

Mediums change paint behavior at a structural level. They alter viscosity, transparency, drying time, or texture.

Additives are more targeted. Ox gall, for example, acts as a surfactant and only addresses surface tension and flow. It does not change the film strength or transparency of the dried paint.

Varnishes and fixatives sit entirely outside the painting process. They are applied to the dry surface as a protective or finishing layer. Some watercolor varnishes add a gloss finish; others are matte. Neither belongs in your painting water.

There is some overlap in the industry. Certain product lines blur the category boundaries by packaging additives as mediums. Reading the application instructions, not just the product name, is the reliable way to sort them out.

Gum Arabic

Gum arabic is the natural binder in virtually all watercolor paint. It holds pigment particles in suspension and creates the paint film that bonds to the paper surface once dry.

You can also buy it separately as a standalone medium. That is where it gets interesting.

What It Does as a Medium

Added to paint or painting water, gum arabic:

• Increases gloss and depth of color on dried paint
• Improves paint transparency for cleaner glazes
• Slows drying time, giving more working time on wet washes
• Makes dried paint easier to lift (useful for corrections)
• Can act as a soft mask when applied to paper before painting

According to Artists Network, adding gum arabic slightly extends drying time and makes colors more transparent. It also raises the gloss of the finished surface, which matters if you are going for a certain depth in layered work.

The soft masking use is underrated. Paint gum arabic on paper, let it dry, then lay a wash over it. The gum creates a partial resist. When you wet the area again, you get soft, feathered edges rather than the crisp hard edge of masking fluid. Completely different character.

How to Use It Without Problems

The mistake most people make: using it straight from the bottle.

Gum arabic should always be diluted with water before use. A common starting ratio is around 20 drops per 8 oz of painting water. Too much gum arabic makes the dried paint brittle and prone to cracking. It also makes the surface overly tacky, which causes issues when laying subsequent washes.

One more thing to be aware of: because gum arabic keeps the paint more soluble, it is not a good choice when you plan to layer multiple washes over each other. Each new wet layer can reactivate and lift the one beneath it. For multi-layer work, use it sparingly or not at all.

Winsor and Newton, Schmincke, and Old Holland all produce professional-grade gum arabic solutions. Old Holland’s formulation uses glycerine alongside the dissolved gum for added flexibility in the dried film.

Ox Gall Liquid

Ox gall is derived from the bile of cattle. Traditionally sourced, though synthetic versions with identical properties are now available from brands like Golden (QoR line) for artists who avoid animal products.

Its only job is to reduce surface tension in water. That single function has a surprisingly large effect on how paint behaves.

What Surface Tension Actually Does to Your Paint

Water has a natural tendency to bead and resist spreading on certain surfaces. Heavily sized paper, smooth hot press sheets, and any paper that has been handled with slightly oily fingers will all resist paint to some degree.

Ox gall breaks that resistance. Add two to four drops per cup of painting water (not directly into the paint) and the paint flows more freely, spreads more evenly, and settles without beading. It behaves the way you expect watercolor to behave on good paper, even when the surface is working against you.

Schmincke limits use of ox gall as a dispersant in their Horadam line specifically to give artists full control of color flow, even on softer papers. That tells you something about how significantly this additive affects spread behavior.

When Ox Gall Helps Most

Wet-on-wet work on resistant paper. Large flat or graduated washes. Any situation where the paint is pulling and puckering instead of laying down smoothly.

You can also stroke it across your palette to reduce paint beading on the mixing surface, which is a small but genuinely useful trick.

Use it lightly. Too much ox gall pushes paint to the edges as it dries, creating hard cauliflower-like blooms that are difficult to control. Two to four drops is the ceiling for most uses.

Watercolor Ground

Watercolor ground is not a paint additive. It is a surface preparation product, applied to a support before painting begins.

Its purpose is to make non-paper surfaces accept watercolor.

What Surfaces It Works On

Applied in thin coats, watercolor ground creates an absorbent, paper-like surface on materials that would normally repel water-based paint completely.

Surfaces that work with watercolor ground:

• Canvas (stretched or panel)
• Wood panels
• Metal
• Glass (with surface abrasion first)
• Hardboard and MDF
• Plaster

Daniel Smith’s watercolor ground, after drying, produces a texture that closely resembles cold press paper. It is slightly more absorbent than paper, so you may need to use less water per mix to avoid over-saturating the surface. Golden’s Absorbent Ground is formulated for a high level of absorbency and is specifically described as paper-like once dry.

Worth knowing: Daniel Smith produces six color variants of their ground, including a Buff Titanium tone for artists who want a warm neutral base rather than stark white. That opens up different starting points for the painting without relying on the support’s natural color.

Application and Common Mistakes

Apply in at least two thin coats, alternating directions between layers. Allow 24 hours between coats. Rushing this step results in uneven absorbency, which shows up as patchy paint behavior later.

For non-porous surfaces like metal or glass, abrade the surface with sandpaper before applying the ground. Without that tooth, the acrylic primer has nothing to grip and will peel.

Heavy washes on watercolor ground tend to lift the ground itself if it has not fully cured. This is a known limitation. Test the surface before committing to a large wash-heavy painting, and give it at least 30 hours to cure on non-porous supports.

It is also worth noting that watercolor ground can be used on existing watercolor paper to cover errors or rework a section. Applied thinly over a dried area you want to repaint, it essentially resets the surface absorbency. Practical for fixing a patch without starting over.

Masking Fluid

Masking fluid is a liquid latex resist. You apply it to paper before painting to protect specific areas from receiving paint. When dry, it peels or rubs off cleanly to reveal untouched white paper underneath.

It is one of the most used mediums in watercolor painting techniques, and also one of the most abused.

Tinted vs. Clear Formulas

Most masking fluids are tinted with a yellow or blue pigment so you can see where you have applied them. That visibility matters when you are masking fine lines or small shapes around complex compositions.

Colourless masking fluid exists for situations where tinted formulas risk staining sensitive paper. On certain papers, the pigment in standard masking fluid can leave a faint color behind even after removal. Clear formulas avoid that risk.

Brands worth knowing:

• Winsor and Newton Art Masking Fluid (tinted yellow)
• Pebeo Drawing Gum (tinted, dip-pen compatible)
• Schmincke Masking Fluid (available tinted and colorless)

The Brush Problem

Masking fluid destroys brushes. Fast.

The latex dries inside the ferrule and on the bristles within minutes of application. Most artists either use a dedicated cheap brush they replace regularly, or coat their brush with dish soap before dipping it in the fluid. The soap creates a barrier that prevents the latex from bonding to the bristles. Rinse immediately after use regardless.

The correct way to apply masking fluid also involves letting it dry fully before painting over it, and waiting until the overlying paint is completely dry before removing it. Pulling masking fluid off wet paper tears the surface. There is no fixing that.

Masking Fluid vs. Gum Arabic as a Resist

These two create very different edges.

Masking fluid produces hard, crisp boundaries, useful for sharp highlights and precise shapes. Gum arabic used as a soft mask produces feathered, painterly edges with partial color bleeding through. They are not interchangeable. Choosing the wrong one for the effect you want is a common mistake in watercolor masking techniques.

FAQ on Watercolor Mediums

What is a watercolor medium?

A watercolor medium is any substance added to paint or painting water to change how it behaves.

Mediums alter properties like drying time, transparency, flow, and texture. They are separate from the paint itself and from tools like brushes or paper.

Do I need watercolor mediums as a beginner?

No. Water and paint are enough to start.

Mediums become useful once you understand how watercolor behaves on its own. Reaching for gum arabic or ox gall before you know the basics adds variables you are not ready to control.

What does gum arabic do in watercolor?

It increases gloss, transparency, and working time when added to paint or painting water.

Gum arabic is the natural binder in watercolor paint. Used separately as a medium, it slows drying, deepens color, and makes dried paint easier to lift.

What is ox gall used for in watercolor painting?

It reduces surface tension so paint flows more evenly across the paper.

Add two to four drops per cup of water. It is especially useful on sized or resistant paper where paint tends to bead. Never add it directly to the paint.

What is masking fluid and how does it work?

Masking fluid is a liquid latex resist applied to paper before painting to protect specific areas from paint.

Once the overlying paint dries, the fluid peels off to reveal clean white paper. It creates hard, crisp edges. Always use a cheap or dedicated brush, as it destroys bristles quickly.

What is granulation medium in watercolor?

It is a medium that causes pigment particles to settle unevenly into the paper surface, creating a speckled, grainy texture.

Any color can be made to granulate with it, not just pigments that naturally do so. Rough paper produces the strongest granulation effect.

Can I use watercolor on canvas or wood?

Yes, but only with proper surface preparation.

Apply watercolor ground in two or more thin coats and allow 24 hours to cure between layers. Brands like Daniel Smith and Golden produce grounds that create a paper-like absorbent surface on canvas, wood, and metal.

What is the difference between iridescent and interference mediums?

Iridescent medium adds a fixed pearlescent sheen to paint. Interference medium shifts color depending on the viewing angle.

Both contain mica particles. Thinner applications produce stronger optical effects for both. Mixing either with matte materials kills the shimmer entirely.

Can I mix different watercolor mediums together?

Technically yes, but it is not recommended until you know how each behaves on its own.

Combining, say, gum arabic and a retarder in the same wash produces unpredictable results. Use one medium at a time. Test on scrap paper before applying to finished work.

Does watercolor medium affect lightfastness or archival quality?

Most professional-grade mediums do not affect the lightfastness of the underlying pigment.

However, excessive gum arabic can make the paint film brittle over time. Retarder used beyond 15% of the mix may prevent proper drying. Stick to manufacturer guidelines and use professional rather than student-grade products.

Conclusion

This article on watercolor mediums covers the full range of substances that change how paint behaves, from gum arabic and ox gall through to granulation medium, iridescent finishes, and watercolor ground.

Each one solves a specific problem. None of them are necessary all at once.

Start with one medium, test it on scrap paper, and understand its effect on paint viscosity, pigment suspension, and drying before moving to the next.

Professional-grade products from Winsor and Newton, Schmincke, and Daniel Smith produce consistent, reliable results. Student-grade versions often do not.

Used well, these mediums give you real control over paint adhesion, wash behavior, and surface texture in ways that water alone never will.

The medium should always serve the painting. Keep it simple and build from there.