Oil Painting Solvents and Mediums: A Safety and Selection Guide

Why solvents matter

Solvents do two jobs in an oil painting studio. First, they thin oil paint so it flows and dries faster (most useful in the lean early layers of a painting). Second, they clean brushes and tools.

The risk is that all solvents evaporate, and what evaporates you breathe. The volatile organic compounds (VOCs) in traditional solvents can cause headaches, dizziness, and over long exposure can do real harm to the nervous system and liver. Choosing the right solvent and ventilating well are the two decisions that matter most.

Turpentine

Distilled gum turpentine is the traditional oil-painter's solvent. It is made from pine resin, has a strong piney smell, evaporates quickly, and is a powerful solvent for natural resins like damar and mastic.

The downsides are well documented. Turpentine has high VOC content, can cause skin sensitisation (dermatitis becomes increasingly common with prolonged exposure), and contributes to respiratory and neurological issues at studio concentrations. It is also a real allergen. Many painters who start their careers fine with turpentine develop a sensitivity after years of use.

Almost no contemporary painter actually needs turpentine. The exception is when working with natural-resin mediums (damar, mastic, copal varnishes), which require a strong solvent to stay in solution. If you are not using those, you can probably skip turpentine entirely.

Odourless mineral spirits

Odourless mineral spirits (OMS) are petroleum-derived solvents from which the most aromatic and toxic fractions have been refined out. The most common artist-grade product is Gamblin's Gamsol, which contains less than 0.005 percent aromatic compounds, well below the threshold considered irritating to most people.

Compared to turpentine, odourless mineral spirits:

• Evaporate much more slowly, which reduces inhalation exposure in a working session.
• Have far lower aromatic content, so the day-to-day risk of chronic harm is significantly reduced.
• Last longer in a brush-cleaning jar before becoming saturated, because slower evaporation leaves the solvent in the jar.
• Are not strong enough to dissolve damar or mastic, which is fine for almost all modern oil-painting workflows.

One important caveat. Because odourless mineral spirits are odourless, they do not warn you when concentrations are rising in poorly ventilated spaces. Painters can be working in unsafe vapour levels without smelling anything. Treat OMS as needing the same ventilation you would give turpentine, even though it feels gentler.

The fat over lean rule

One of the oldest rules in oil painting: each layer should contain more oil than the one below it. Layers that are richer in oil (fat) on top of layers that are leaner (more solvent, less oil) dry slowly enough to avoid cracking. Reverse the order and the upper layer dries faster than the lower, which forces the paint film into tension and eventually splits.

In practice, this means using the most solvent in the first layer (a thinned underpainting), reducing solvent through the middle layers, and using only oil-rich medium or pure paint in the final layers. Knowing how much solvent and medium you use in each layer is more important than which specific brand.

Mediums in plain language

A medium is anything you mix into oil paint to change how it handles. There are dozens on the market, but they fall into a few clear categories:

• Drying oils (linseed, walnut, safflower, poppy). Slow drying, increase flow, add gloss. Linseed is the most common. Walnut yellows less but dries slower. Safflower and poppy yellow least but dry slowest of all.
• Stand oil and sun-thickened oils. Pre-polymerised drying oils. Smoother flow, slower drying, very glossy. Used in glazing mediums.
• Alkyd-based mediums (Liquin, Galkyd). Synthetic resin in oil. Speed up drying substantially. Useful for layered work, but they can become insoluble over time, which makes future restoration harder.
• Solvent-only thinning. Just OMS. Strips oil from the paint and produces a leaner, faster-drying layer. Suitable only for early underpaintings. Avoid in later layers.
• Resin mediums (damar, mastic). Add gloss and toughness. Require turpentine to dissolve. Less common in contemporary practice.

Most working oil painters use one solvent (OMS) and one or two mediums (linseed oil and an alkyd) and stick with them for years. Variety in mediums is rarely worth the complication.

Ventilation that actually works

Most studio safety problems are ventilation problems. Solvent vapours are heavier than air, so they pool near the floor, where you breathe when sitting at an easel. A few practical fixes:

• Cross ventilation. Open a window on each side of the room, with the prevailing airflow moving across your easel rather than over your head.
• An exhaust fan low to the floor. A simple box fan in a window, set to blow out, with the fan as low as practical, removes pooled vapour effectively.
• Closed solvent containers. Keep brush-cleaning jars covered when not in use. Open jars are the largest single source of solvent vapour in most studios.
• No solvent in the living space. Studios that double as bedrooms or living rooms need a strict end-of-day cleanup. Cap and seal everything before you leave.

Rag disposal and fire risk

Oil-soaked rags are a real fire hazard. The drying process of linseed oil is exothermic; it generates heat. Rags piled together in a closed bin can self-heat to ignition. House fires from oil-soaked rags happen every year and are completely preventable.

Two safe options:

• Submerge rags in water in a sealed metal container until disposal. Water prevents oxidation and removes the heat hazard.
• Dry rags flat and outdoors on a non-flammable surface (concrete, metal) until completely hard. Once oxidised, the rags are no longer a fire risk and can be disposed of in normal waste.

Never crumple oil-soaked rags into a closed plastic bag or drop them into a normal household bin. The risk is small but it is real.

Brush cleaning without a solvent jar

Many painters now skip the solvent jar entirely. The simplest alternative:

1. Wipe most of the paint off the brush on a clean rag or paper towel.
2. Work a small amount of safflower or walnut oil into the bristles, then wipe.
3. Rinse with mild soap (Master's Brush Cleaner or a simple olive-oil bar soap) under cool water until the lather runs clean.
4. Reshape the brush with your fingers and store flat or bristles up.

This adds a minute or two to clean-up but eliminates the single biggest source of solvent vapour in a studio. For most painters, it is a clear net win.

A simple safer studio

The configuration most working oil painters land on:

• One bottle of odourless mineral spirits, used sparingly for early layers.
• One bottle of linseed or walnut oil for the main mediums.
• Optional: one alkyd medium for faster drying.
• No turpentine unless you are working with natural-resin varnishes.
• Cross ventilation and a low exhaust fan.
• Oil and water buckets for rag disposal.
• Soap-and-water brush cleaning.

The work does not suffer from any of this. The painter breathes a great deal less, and the studio becomes a place you can spend long hours without paying for it later.