Oil painting mediums confuse beginners more than almost any other topic. Tubes of paint sit ready, but which liquid should mix with them?
Your medium choice affects how long your painting lasts. It determines whether colors stay bright or turn yellow. The right medium makes painting feel natural, while the wrong one causes frustration.
What Are Oil Painting Mediums And Why Do You Need Them?
Paint straight from the tube feels thick and stiff. Paint mediums change how paint behaves on your brush and canvas. They thin paint for smooth blending or thicken it for bold texture.
Mediums control four main properties of oil paint. They adjust thickness and flow across the canvas. They speed up or slow down drying time between painting sessions. They shift the final look from glossy to flat. They increase transparency for building up layers of color.
The Three Main Categories of Oil Painting Mediums
1. Drying Oils
Drying oils form the base ingredient in oil paint itself. These oils harden when exposed to oxygen over time. Adding small amounts makes paint more flexible and transparent.
Linseed Oil
Linseed oil creates the strongest paint film when dry. It dries at a moderate pace, usually within several days. Paintings made with linseed oil have survived hundreds of years. This oil has one drawback worth knowing. It can yellow slightly if stored in darkness. However, exposure to light reverses this yellowing within days.
Stand Oil
Stand oil is linseed oil that underwent heat processing. The treatment thickens it to a syrup-like consistency. It creates an even smoother, more level paint surface. This processed oil dries faster than regular linseed oil. It produces a glossy, enamel-like finish when dry. Painters favor it for final layers requiring fine detail.
Safflower Oil
Safflower oil appears much paler than linseed oil. It yellows less over time, protecting light colors. Many manufacturers use it specifically for white paint. This oil dries slower than linseed by two or three days. Apply it only in final painting layers. Early layers need faster-drying oils for stability.
Walnut Oil
Walnut oil has been used longer than linseed historically. It appears almost colorless compared to other drying oils. Light colors maintain their coolness without yellowing. The dried walnut oil film proves stronger than poppy oil. It dries at roughly the same speed as linseed. Painters choose it for detailed work requiring precision.
Poppy Oil
Poppy oil looks extremely pale and transparent. It yellows less than any other common painting oil. Manufacturers sometimes use it in white and pale blue paints. Drying takes five to seven days on average. This slow pace suits painters working wet-into-wet for extended periods. The long open time allows endless blending.
2. Solvents: Thinners and Cleaners
Solvents thin paint and clean brushes between color changes. They evaporate into the air rather than drying like oils. Use them sparingly to avoid weakening paint structure.
Odorless Mineral Spirits (OMS)
Odorless mineral spirits replaced turpentine in most modern studios. The fumes remain much less noticeable than traditional solvents. Brands like Gamsol offer refined, artist-grade versions. OMS thins paint for initial blocking-in stages. It cleans brushes between colors during painting sessions. The solvent settles in jars, allowing you to reuse it.
Don't mistake "odorless" for "non-toxic" despite what labels claim. Use adequate ventilation even with refined versions. Small amounts pose minimal risk when handled properly.
Traditional Turpentine
Turpentine comes from pine tree resin. Artists used it for centuries before modern alternatives appeared. The smell proves strong and distinctive. Some painters prefer its traditional working properties. It dissolves paint slightly differently than mineral spirits. The cost has risen compared to modern solvents.
Turpentine requires good studio ventilation. The fumes affect some people more than others. Test your tolerance before committing to regular use.
Spike Lavender Oil
Spike lavender oil is technically a solvent despite its name. It carries a strong herbal scent that divides opinion. Marketing promotes it as a natural, healthier alternative. The solvent works fine for thinning paint in mediums. However, it fails as a brush cleaner. Paint particles don't settle in jars like they do with mineral spirits.
This makes spike oil expensive and wasteful for studio use. You must replace large quantities frequently. The environmental benefits disappear when you can't reuse it.
3. Modern Alkyd Mediums
Alkyds combine resin with oil painting properties. They dramatically accelerate drying time to just hours. Outdoor and single-session painters favor these products.
Liquin & Galkyd
Liquin and Galkyd represent the two most popular alkyd brands. Both reduce drying time from days to hours. They increase gloss and improve paint flow simultaneously. These mediums work well for quick layering techniques. Painters can build up multiple layers in one day. The convenience appeals to artists with limited studio time.
Alkyds carry a distinct chemical smell. The odor bothers some painters more than traditional solvents. Question marks remain about mystery ingredients in mass-produced formulas.
What "Fat Over Lean" Really Means
Fat over lean describes oil content in successive paint layers. Each new layer needs more oil than the one beneath. This prevents cracking as the painting ages. Oil-rich layers dry slower and remain flexible longer. Lean layers with more solvent dry faster and harder. A slow-drying layer under a fast-drying one causes cracks.
Practical Application
The rule sounds simple but multiple factors affect drying speed. Different pigments dry at different rates naturally. Canvas preparation changes how fast lower layers set. Temperature and humidity in your studio matter too. Cold, damp conditions slow drying dramatically. Warm, dry air helps paint cure faster.
For First Layers:
Use more solvent and less oil in initial stages. Thin paint and scrub it on with bristle brushes. The lean mixture dries quickly, creating a stable foundation. Fast-drying pigments work best for underlayers. Raw umber and burnt umber both dry rapidly. Lead white also cures quickly when available.
For Final Layers:
Add more oil and reduce solvent as you progress. Stand oil works well for detailed final passages. The increased oil content keeps upper layers flexible. Thick paint requires extra care with oil content. Heavy impasto needs sufficient oil to prevent cracking. Balance thickness with flexibility through proper medium ratios.
Factors That Affect Drying Time
Pigment choice influences how quickly paint sets. Earth colors dry much faster than most others. Ivory black takes weeks to cure completely. Your painting surface affects oil absorption significantly. Chalk gesso grounds pull oil from paint, speeding drying. Acrylic gesso absorbs less and dries slower.
Stand oil dries faster than regular linseed despite being thicker. This seems counterintuitive but heat processing changes its chemistry. The relationship between viscosity and drying isn't linear.
Simple Medium Recipes for Beginners
Lean Medium (For Initial Layers)
Mix two parts linseed oil with one part odorless mineral spirits. This thin mixture suits early blocking-in stages. The higher solvent content makes it lean and fast-drying. Brush this medium sparingly into paint on your palette. The thin consistency allows paint to spread smoothly. Initial layers dry within two to three days.
Fat Medium (For Final Layers)
Combine equal parts linseed oil and stand oil only. No solvent enters this mixture for upper layers. The pure oil content makes it appropriately fat. This thicker medium supports fine detail work beautifully. The stand oil component creates a smooth, level surface. Drying takes longer but produces excellent results.
Beginner's All-Purpose Recipe
Mix three parts odorless mineral spirits with one part linseed oil. This versatile formula works for most painting situations. The ratio provides good flow without excessive thinning. Keep small amounts in sealed glass or metal cups. Dip your brush and blend on the palette. A little goes much further than beginners expect.
Solvent-Free Alternative
Use walnut oil from the grocery store as your only medium. Verify the label contains no added vitamin E. This pure oil approach eliminates solvent exposure. The light drying properties feel similar to diluted linseed. However, it limits you to single-session painting. Building layers becomes difficult without solvent to lean paint.
Practical Tips In Applying Your Medium
How Much Medium to Use
Less is more when adding medium to paint. Start with a tiny amount on your brush. You can always add more if needed. Excess medium weakens paint structure over time. Too much oil causes paint to wrinkle as it dries. Pigment particles need to outnumber oil molecules for stability.
Most beginners add three times too much medium. The paint should feel slightly easier to move. It shouldn't look glossy or wet on the palette.
The "Couch" Technique
A couch means spreading medium directly on the canvas. Apply a thin layer before painting into that area. This makes subsequent paint glide on more smoothly. Use a makeup sponge to spread the medium evenly. Flip the sponge and blot up excess with the dry side. Only a whisper-thin film should remain.
This technique works well for smooth backgrounds. It helps when painting over dried layers too. The couch reactivates the surface for better blending.
When NOT to Use Medium
Thick impasto passages need paint straight from the tube. Medium thins paint and reduces its ability to hold texture. Palette knife work requires pure, unmodified paint. Some pigments contain enough oil already. Adding more creates problems rather than solutions. Watch for paint that already flows easily.
Dark passages often work better without added medium. Excess oil in darks causes yellowing over time. Keep shadows lean for better color preservation.
Varnishing: The Final Step
When to Varnish
Oil paintings need months to cure before final varnishing. Thin layers dry in six months typically. Thick paint requires a year or more to fully harden. Touch-dry paint feels solid on the surface only. Chemical changes continue deep within paint layers. Premature varnishing traps solvents and causes problems.
Types of Varnish
Retouching Varnish
Retouching varnish goes on touch-dry paintings needing immediate display. It forms a thin, temporary protective layer. The dilute formula dries fast and evens out sheen. Spray versions dry most reliably across the surface. Brush application works but requires skill. This varnish protects paintings until final varnishing becomes possible.
Apply picture varnish over retouching varnish once painting cures. The temporary layer doesn't interfere with permanent protection. Clean dust off carefully before the final coat.
Picture Varnish
Picture varnish provides permanent protection for fully cured paintings. It contains more resin than retouching varnish. The dried layer resists damage and unifies surface appearance. This varnish comes in gloss, satin, and matte finishes. Gloss shows colors at maximum intensity. Matte reduces reflections for viewing under bright lights.
Apply picture varnish with a wide, soft brush. Work in a dust-free room with good lighting. Multiple thin coats work better than one thick application.
Matte Varnish As Alternative To Matte Medium
Matte varnish provides the flattest possible finish. Beeswax or matting agents reduce shine. Apply it as the final step rather than mixing into paint. This approach preserves paint structure throughout layers. Mixed-in matte mediums can weaken paint film. Varnish offers the same visual effect more safely.
Some painters prefer natural paint sheen without varnish. Oil paint dries to a subtle satin finish. Personal preference guides this final decision.
Plein Air Easel Stand Recommendations:
Conclusion
Oil painting mediums unlock control over your materials. They transform stiff tube paint into responsive, flexible color. Drying oils, solvents, and alkyds each serve specific purposes in your process. Start with basic combinations before exploring specialty mediums. Practice with small amounts until you feel the difference each medium creates.