Stepping into the world of oil painting is like opening a door to endless possibilities. The rich colours, the buttery texture, the slow drying time that allows for blending and contemplation – it’s captivating. But beyond the tubes of pigment lies another layer of magic, a realm of liquids and gels that can fundamentally change how your paint behaves and how your finished artwork looks and lasts. We’re talking about oil painting mediums and varnishes, the often-unsung heroes that give artists incredible control over their craft.
Many beginners start by using paint straight from the tube, perhaps thinning it slightly with a solvent like turpentine or mineral spirits. While perfectly valid, this only scratches the surface. Mediums are additives designed to be mixed directly into your oil paints to alter their characteristics. Think of them as modifiers, allowing you to tailor the paint’s consistency, drying rate, transparency, and final sheen to suit your specific needs and artistic vision.
Understanding Oil Painting Mediums
Why bother adding anything to your paint? Because the paint straight from the tube might not be ideal for every technique. Want to create thin, transparent glazes like the Old Masters? You’ll need a medium. Need your paint to dry faster so you can layer more quickly? There’s a medium for that. Want thick, juicy brushstrokes that hold their shape (impasto)? A specific medium can help achieve that too. They essentially extend the expressive range of your paints.
Mediums typically consist of a binder (usually an oil, like linseed or poppy) and often a solvent (like turpentine or mineral spirits) to affect viscosity and drying time. Some modern mediums use synthetic resins. The key is understanding how different components influence the paint.
The Classics: Traditional Oils
These are the mediums derived from natural plant sources, used by painters for centuries.
Linseed Oil: This is the most common and traditional binder used in oil paints themselves, and thus a very popular medium. It’s known for creating a strong, durable paint film. However, it has a tendency to yellow over time, which can be noticeable in lighter colours. It dries at a moderate rate.
- Refined Linseed Oil: The standard, treated to remove impurities.
- Cold-Pressed Linseed Oil: Extracted without heat, considered higher quality by some, potentially less yellowing but dries slightly slower.
- Stand Oil: Linseed oil that has been polymerized by heating it in the absence of oxygen. It’s thicker, flows well, levels brushstrokes, yellows much less than regular linseed oil, and creates a tough, glossy, enamel-like finish. It dries very slowly. Often mixed with a solvent to improve workability.
Poppy Seed Oil: Paler than linseed oil and much less prone to yellowing, making it a favourite for whites, blues, and pale colours. However, it dries significantly slower than linseed oil and forms a slightly less durable paint film. Overuse can potentially lead to cracking if applied over faster-drying layers.
Safflower Oil: Very similar to poppy oil in its properties – pale, slow drying, and less yellowing than linseed. It’s often used as a binder in commercial white and pale blue paints for this reason. Like poppy oil, it creates a less robust paint film compared to linseed oil.
Walnut Oil: Used historically (prominently during the Renaissance), walnut oil offers a balance. It yellows less than linseed oil but more than poppy or safflower oil. Its drying time is moderate, often falling between linseed and poppy oil. It provides good handling properties and a durable film.
The Accelerators: Alkyd Mediums
If the slow drying time of traditional oils tries your patience, alkyd mediums might be your solution. These are synthetic resin-based mediums that significantly speed up the drying process. An oil paint layer mixed with an alkyd medium can often be touch-dry overnight or within 24 hours, compared to days or weeks for traditional oils.
Alkyds come in various formulations, offering different levels of gloss, fluidity, or impasto qualities (like Liquin Original, Liquin Fine Detail, Liquin Impasto by Winsor & Newton, or Galkyd by Gamblin). They are very popular for their convenience, allowing artists to build layers much more quickly. Some artists find they have a slightly different ‘feel’ or handling property compared to traditional oils, sometimes described as slightly more ‘slippery’ or ‘plastic’.
Important Note on ‘Fat Over Lean’: This is a fundamental principle in oil painting, especially when layering. ‘Fat’ refers to paint with a higher oil content (or medium content), while ‘lean’ refers to paint with less oil, often thinned with solvent. You should always apply fatter (more oil-rich, slower drying) layers over leaner (less oil-rich, faster drying) layers. Reversing this can cause the upper layers to dry faster and crack as the lower layers continue to shift and dry.
The Thinners: Solvents
Solvents don’t add oil; they dilute the paint, making it thinner and speeding up the drying time by evaporation. They are crucial for creating washes, underpaintings, and for cleaning brushes.
Turpentine: Distilled pine resin. The traditional solvent. It has strong fumes and requires good ventilation. Gum turpentine is generally preferred for painting over mineral turpentine.
Mineral Spirits (White Spirit): Petroleum distillate. Less aromatic than turpentine but still requires good ventilation. Often used for brush cleaning and sometimes for thinning paint in initial layers.
Odorless Mineral Spirits (OMS): Further refined mineral spirits where the aromatic solvents (which cause the strong smell and are considered the most harmful) have been removed. While safer regarding fumes, they are still solvents and require ventilation. They evaporate slower than turpentine.
Protecting Your Masterpiece: Varnishes
Once your oil painting is completely dry (and this takes longer than you might think!), applying a final varnish is a crucial step for preservation and appearance. Varnish provides a protective layer against dirt, dust, grime, and UV radiation, which can fade pigments over time. It also serves an aesthetic purpose, unifying the final sheen of the painting – some areas might dry glossy, others matte, and varnish can give it a consistent finish (gloss, satin, or matte).
Crucially, varnish is intended to be removable. Over decades, varnish itself can yellow or collect stubborn grime. A professional conservator can remove the old varnish layer (along with the accumulated dirt) and apply a fresh coat, restoring the painting’s original appearance without harming the paint layers beneath.
Wait Before Varnishing! Oil paint needs to cure fully, not just be touch-dry. This process involves oxidation and polymerization, which can take 6 months to a year, or even longer for very thick applications (impasto). Varnishing too early can trap solvents and prevent proper curing, potentially leading to cracking or a cloudy varnish layer later on. Patience is key.
Types of Varnishes
Like mediums, varnishes come in traditional and modern varieties.
Damar Varnish: A traditional natural resin (from the Damar tree) dissolved in turpentine. It provides a high-gloss finish and saturates colours beautifully. However, Damar is known to become brittle and yellow significantly over time. While removable, its tendency to yellow is a major drawback for long-term preservation.
Synthetic Varnishes: These are now widely recommended by conservators due to their stability. They are typically based on synthetic resins like ketone or acrylic dissolved in mineral spirits or other solvents.
- MSA Varnish (Mineral Spirit Acrylic): A popular choice, known for its clarity, UV protection, and non-yellowing properties. Available in gloss, satin, and matte.
- Gamvar (Gamblin): Another highly regarded synthetic varnish developed in collaboration with the National Gallery of Art. It’s virtually odourless, non-yellowing, easily removable with Gamsol (Gamblin’s OMS), and saturates colours effectively. Available in gloss, satin, and matte.
Synthetic varnishes offer better longevity and stability compared to Damar, making them the preferred choice for many contemporary artists concerned with archival quality.
Retouch Varnish: This is a much thinner varnish, often a diluted version of a final varnish. It’s not intended as the final protective layer. Its purpose is to temporarily restore colours in ‘sunken-in’ areas (where the paint has dried dull because the oil has been absorbed by the layer below) during the painting process, allowing you to accurately judge colours and values. It can also provide minimal protection if a painting needs to be handled or transported before it’s ready for final varnishing.
Application Tips
Always apply varnish in a clean, dust-free environment. Ensure the painting is completely dry. Whether brushing or spraying, apply thin, even coats. It’s often better to apply two thin coats than one thick one. Let the first coat dry completely before applying the second, usually orienting your strokes at 90 degrees to the first coat for even coverage if brushing.
Experimentation is Key
Reading about mediums and varnishes is one thing; using them is another. The best way to understand how they affect your paint and your process is to experiment. Mix small amounts of different mediums with your paint on a palette or a test canvas. Observe the changes in handling, drying time, and appearance. Try glazing with a stand oil mixture versus an alkyd medium. See how different varnishes affect the final look of a test piece.
Understanding these tools empowers you to move beyond the limitations of paint straight from the tube. They allow for nuanced control, enabling techniques from delicate, transparent glazes to bold, textured impasto. They help ensure that the artwork you pour your time and effort into not only looks the way you envision but also stands the test of time. So, embrace the possibilities, mix it up, and see where these fascinating additions can take your oil painting journey.
