Quick answer: Paint mediums are liquids or gels you mix into paint to change how it handles, dries or looks, without simply diluting it the way water or solvent does. Most are made from the same kind of binder that holds the paint together, such as acrylic polymer, drying oil or gum arabic, so they can alter gloss, transparency, flow, texture and drying time while keeping the paint film strong. The word “medium” is also used for the type of paint itself, as in “oil is my medium.”
The term confuses a lot of new painters because it carries two meanings at once. A teacher might ask which medium you work in, meaning watercolor, acrylic or oil. A supply store shelf labeled “mediums,” on the other hand, holds bottles and jars of additives. Both uses are correct. This explainer covers what paint mediums are in each sense, what the additive kind is made of, what each type does, and how to use them without weakening your painting.
If you already know what effect you want and just need a product, the comparison of the best paint mediums for painting and craft projects groups options by what they change.
What Are Mediums of Painting? The Two Meanings
Medium as the type of paint
In art history and gallery labels, “medium” describes the material a work is made with. “Oil on canvas,” “watercolor on paper” and “acrylic on panel” all name a medium and a support. In this sense, the medium is defined mostly by the binder that holds the pigment: linseed oil for oil paint, gum arabic for watercolor and gouache, acrylic polymer emulsion for acrylic, egg yolk for tempera and beeswax for encaustic.
Medium as an additive
In the studio, a “painting medium” usually means something you add to paint on the palette. Linseed oil stirred into oil paint, gloss gel folded into acrylic, or gum arabic dropped into a watercolor wash are all mediums in this second sense. They modify the paint rather than replace it.
The two meanings are linked: an additive medium is usually a concentrated or modified version of the paint’s own binder. That is why acrylic mediums mix cleanly with acrylic paint and oil mediums with oil paint, but not the other way around.
What Is Paint Made Of, and Where Mediums Fit
Every paint has three basic parts:
- Pigment: the finely ground colored particles.
- Binder (or vehicle): the film-forming material that glues pigment together and to the surface.
- Diluent: something that thins the paint and then evaporates, like water or mineral spirits.
A diluent alone spreads the binder thinner. Add too much and there is not enough binder left to hold the pigment, which can lead to a chalky, weak film. A medium adds binder or modifies it, so you can make paint thinner, glossier or slower without starving the pigment. That distinction is the single most useful thing to understand about mediums.
What Do Paint Mediums Actually Do?
Depending on the formula, a medium can change one or several properties:
| Property | What changes | Typical medium type |
|---|---|---|
| Flow | Paint levels out and brushes more smoothly | Flow improvers, fluid mediums, refined linseed oil |
| Transparency | Color becomes a see-through glaze | Glazing mediums, gloss gels |
| Sheen | Dries glossier or flatter | Gloss or matte mediums |
| Body | Paint holds peaks and knife marks | Heavy gels, impasto mediums, cold wax |
| Drying time | Dries faster or slower | Alkyd mediums (faster), retarders and open mediums (slower) |
| Texture | Adds grit, fibers or granular effects | Pumice gels, modeling paste, granulation medium |
| Absorbency / adhesion | Surface accepts paint differently | Ground mediums, watercolor grounds |
| Special uses | Fabric, pouring, iridescence | Textile medium, pouring medium, interference mediums |
Acrylic Mediums Explained
Acrylic has the widest range of mediums because the polymer emulsion that binds it can be produced in many viscosities. Since most acrylic mediums are essentially paint without pigment, you can usually add a lot of them without harming adhesion.
- Gloss and matte mediums: liquid binders that thin paint while keeping film strength. Matte versions add a flattening agent that can cloud dark colors if layered heavily.
- Gel mediums: thicker, from soft to extra heavy. They extend paint, increase transparency, hold texture and work well as collage glue.
- Modeling paste: a stiff, opaque filler for sculptural texture. It dries harder than gel and can be sanded.
- Retarders and open mediums: slow drying to allow blending. Retarders have recommended limits on the label, because too much can leave the film tacky.
- Pouring medium: creates a fluid, self-leveling paint for poured and flow-art techniques.
- Fabric or textile medium: keeps acrylic flexible on cloth and improves wash resistance after heat setting.
- Flow improvers: reduce surface tension so paint spreads evenly, helpful for flat color fields and fine lines.
A common rule of thumb is to keep plain water additions to around a third of the mix or less for acrylics if you want a durable film, and use a medium when you need thinner paint beyond that. Brand guidance varies, so check the label.
Oil Painting Mediums Explained
Oil mediums work differently because oil paint dries by oxidation rather than evaporation. The paint absorbs oxygen and slowly forms a solid film. Mediums change that process and the feel of the paint.
- Refined linseed oil: increases flow and gloss, slows drying slightly and adds flexibility. The traditional baseline oil medium.
- Stand oil: thickened, heat-treated linseed oil. It levels into smooth, enamel-like glazes and resists yellowing better than raw oil, but dries slowly.
- Safflower and poppy oil: paler oils used with whites and blues, slower drying and slightly weaker films.
- Alkyd mediums: synthetic resin mediums that speed drying, often to touch-dry within a day for thin layers. Useful for glazing and for painters on a schedule.
- Solvents: odorless mineral spirits or turpentine thin paint for early layers. Technically diluents, not mediums, though they are often combined with oil to make a “painting medium.”
- Cold wax medium: beeswax softened with solvent and resin, for matte, textural and scraped work.
- Impasto mediums: add body for thick, knife-applied paint and help thick passages dry more evenly.
Oil mediums also bring the “fat over lean” principle into play. Each layer should contain the same or more oil than the one below it. Lean (solvent-heavy) layers go first, fatter (oil-rich) layers on top. Reversing that order can cause cracking as layers dry at different rates.
Watercolor and Gouache Mediums Explained
Watercolor and gouache share a gum arabic binder, so their mediums overlap. They are used in small amounts, often a few drops in the water or the wash.
- Gum arabic: increases gloss and transparency, intensifies color and slows lifting slightly. Too much can make paint brittle and shiny.
- Ox gall or wetting agent: reduces surface tension so washes flow evenly on hard-sized paper.
- Granulation medium: encourages pigment to separate into a speckled texture, even with colors that usually lie smooth.
- Glycerin or blending medium: keeps washes wet longer for softer blends, useful in hot, dry rooms.
- Iridescent and interference mediums: add shimmer.
- Watercolor ground: lets you prepare canvas, wood or primed boards to accept watercolor like paper does.
Masking fluid is usually sold alongside these, but it is a resist rather than a medium, since it blocks paint instead of changing it.
Painting Mediums and Techniques: Which Medium Suits Which Approach
Matching medium to technique matters more than collecting many bottles. Here is a quick pairing guide:
| Technique | Acrylic | Oil | Watercolor / gouache |
|---|---|---|---|
| Glazing | Gloss medium or soft gel | Stand oil or alkyd glazing medium | Gum arabic in thin washes |
| Wet blending | Retarder or open medium | Linseed oil; paint is naturally slow | Glycerin-based blending medium |
| Impasto | Heavy gel, modeling paste | Impasto medium, cold wax | Not typical; use gouache thickly or texture ground |
| Pouring | Pouring medium | Rarely used; oil is too slow | Not typical |
| Flat color fields | Flow improver, fluid medium | Alkyd medium for even drying | Ox gall in wash water |
| Mixed media | Gel medium as glue and sealer | Cold wax with collage elements | Watercolor ground on non-paper surfaces |
Beginners trying to decide which type of paint to commit to may find the comparison on the easiest painting medium for beginners useful before investing in additives.
How to Use Medium Without Weakening Your Paint
Mediums are forgiving once you follow a few principles:
- Match the system. Use acrylic mediums with acrylic paint, oil mediums with oil paint, and watercolor mediums with watercolor or gouache. Crossing systems rarely bonds well.
- Start with small ratios. Add medium a little at a time with a palette knife, roughly 10–20% to start, then judge the effect. Many acrylic gels can go far higher; oil and watercolor additives usually need restraint.
- Mix thoroughly. Streaks of unmixed medium can dry with different gloss or texture from the surrounding paint.
- Test on scrap. Mediums can change color temperature and value, and matte mediums may lighten dark mixes. Paint a test swatch and let it dry before committing.
- Read label limits. Retarders, driers and some flow aids have maximum recommended amounts. Exceeding them can cause tackiness, wrinkling or poor adhesion.
- Respect layer order in oils. Increase oil content as you build layers, not the reverse.
- Allow proper curing. Thick gel or impasto layers can look dry on the surface while still soft underneath. Give them extra time before varnishing.
Mediums vs Varnish vs Primer: What’s the Difference?
These products are often shelved together, but they do different jobs:
- Primer or gesso goes on the surface before painting to seal it and give paint something to grip.
- Medium is mixed into paint during painting to modify it.
- Varnish goes on top of a finished, fully dry painting to protect it and unify the sheen. Many varnishes are removable for future cleaning.
Some acrylic mediums can act as an isolation coat between the painting and a final varnish, but a medium is not a substitute for a proper varnish when long-term protection is the goal.
Common Mistakes With Paint Mediums
- Using solvent or water instead of medium for heavy thinning. The result can be underbound, dusty paint.
- Overusing matte medium in dark layers. It can leave a cloudy haze.
- Adding too much oil to oil paint. Excess oil can wrinkle, yellow or stay soft longer than expected.
- Mixing systems. Oil-based mediums in acrylics, or acrylic gel in watercolor, lead to separation or poor adhesion.
- Varnishing too soon. Thick medium-rich layers need longer to cure.
- Skipping safety. Solvent-based oil mediums need ventilation, and oil-soaked rags should be laid flat to dry or stored in a sealed metal container, since they can self-heat.
Which Paint Mediums Should Beginners Start With?
You do not need a shelf of bottles. A small starting set covers most needs:
- Acrylic painters: one gloss or satin medium, one soft or regular gel, and possibly a retarder if blending feels rushed.
- Oil painters: refined linseed oil and odorless mineral spirits, then an alkyd medium later if drying time is a problem.
- Watercolor painters: gum arabic, with granulation or blending medium as optional extras.
Learn what those do before adding specialty products. Most interesting effects come from a few versatile mediums used well.
FAQs
What are mediums for art in simple terms?
In simple terms, an art medium is either the material you make art with, such as watercolor or oil paint, or a substance you mix into paint to change its behavior. Context tells you which meaning is intended.
Is water a medium for acrylic paint?
Water is a diluent rather than a true medium. It thins acrylic but does not add binder, so large amounts can weaken the paint film. Acrylic mediums thin or modify paint while keeping it strong.
Do I need a medium to paint?
No. Many paintings use paint straight from the tube. Mediums are useful when you want effects the tube paint cannot give, such as glazing, more texture or a different drying time.
Can you mix different paint mediums together?
Within one paint system, usually yes. Many acrylic mediums intermix, and oil painters often combine oil, resin and solvent. Test combinations on scrap first, and do not mix acrylic and oil mediums.
What is the most common oil painting medium?
Refined linseed oil, often combined with a solvent in early layers, is the traditional and most widely used oil medium. Alkyd mediums are also very common today for faster drying.
How much medium should I add to paint?
Start with roughly 10–20% medium and adjust by eye. Acrylic gels tolerate much higher amounts, while oil additives, retarders and watercolor mediums are best used sparingly. Always follow any label limits.
Final Thoughts
Paint mediums are simply tools for adjusting a paint’s binder: more of it, a thicker form of it, or a modified version that dries faster, slower, glossier or flatter. Once you see them that way, choosing one gets much easier. Decide what you want to change, pick the medium designed for that change in your paint system, and test it on scrap. For specific options sorted by acrylic, oil and watercolor use, browse our list of top medium picks for artists and crafters.
