Oil painting holds a certain magic, doesn’t it? The rich colours, the buttery texture, the way light interacts with the surface – it’s captivated artists for centuries. But straight out of the tube isn’t the only way to work. Experienced painters know that understanding and utilising mediums and varnishes is key to unlocking the full potential of oils, allowing for greater control over handling properties, drying times, and the final appearance and longevity of their work.
Unlocking Potential: A Look at Oil Painting Mediums
Think of mediums as modifiers for your oil paint. They are essentially liquids you mix into your paint to change its characteristics. Do you want your paint to flow more easily for fine detail or glazing? Do you need it to dry faster to build layers quickly? Or perhaps you want to increase its gloss or create thick, impasto textures? There’s likely a medium designed for that specific purpose. Adding the right medium can transform your painting process and the final result.
The Foundation: Drying Oils
The binder in traditional oil paint is, naturally, oil. Adding more oil, or a specific type of oil, is the most fundamental way to alter your paint. Different oils have distinct properties:
- Linseed Oil: This is the workhorse, the most traditional and common drying oil used in oil painting. It creates a strong, durable paint film. Refined Linseed Oil is the standard, offering moderate drying time and some yellowing over time. Cold-Pressed Linseed Oil is often considered higher quality, potentially offering better clarity, but it can yellow more noticeably. Stand Oil is linseed oil that has been polymerized by heating, resulting in a thicker, honey-like consistency that levels brushstrokes, increases gloss, and yellows less than regular linseed oil, though it dries slower.
- Poppy Oil: Paler than linseed oil, poppy oil is often favoured for whites and light blues because it yellows significantly less. However, it dries much slower and creates a slightly less robust paint film compared to linseed oil. Overuse can potentially lead to cracking if applied over faster-drying layers.
- Safflower Oil: Similar to poppy oil, safflower oil offers less yellowing than linseed oil and is another good choice for pale colours. Its drying time and film strength are generally considered intermediate between linseed and poppy oil. Many modern paint manufacturers use safflower oil in their lighter colours.
- Walnut Oil: Used since the Renaissance, walnut oil provides good handling properties, yellows less than linseed oil (though perhaps more than poppy or safflower), and dries at a moderate rate. It was a favourite of some Old Masters.
Using these oils allows you to increase the transparency and flow of your paint. Adding more oil generally slows drying time (except for maybe some specific formulations) and increases gloss. The key is consistency – don’t make radical shifts in the oil content between layers, especially avoid oil-rich layers under leaner (less oil) ones, to prevent cracking.
Speeding Things Up: Alkyd Mediums
For artists frustrated by the slow drying time of traditional oils, alkyd mediums are a game-changer. Alkyds are synthetic resins dissolved in a solvent. When mixed with oil paints, they significantly accelerate the drying process, often making paint touch-dry within 18-24 hours, allowing for rapid layering. Popular examples include Liquin Original, Galkyd, and Neo Megilp. They come in various consistencies, from fluid to gel-like, and can increase gloss and transparency. While very convenient, some artists find they handle differently than traditional oils, feeling slightly ‘stickier’ or having a distinct smell.
Thinning and Cleaning: Solvents
Solvents don’t form part of the final paint film in the same way oils do; their primary role is to dilute the paint, making it thinner and more fluid, and to clean brushes and palettes. Adding solvent makes the paint ‘leaner’.
- Turpentine: Distilled from pine resin, genuine gum turpentine is the traditional solvent. It has a strong, distinctive odour and evaporates relatively quickly. Many artists love its working properties.
- Mineral Spirits (White Spirit): Petroleum distillates, such as Gamsol, Turpenoid, or Sansodor, are generally less odorous and less irritating than turpentine for many users. They are effective thinners and cleaners. Odorless Mineral Spirits (OMS) have had the more harmful aromatic components removed, making them safer for studio use, though good ventilation is always essential.
It’s crucial to use solvents judiciously within the paint itself. Too much solvent can break down the oil binder, leading to an underbound paint film that is weak, chalky, and prone to cracking or flaking off the canvas. A common rule is to use solvents more generously in the initial, thinner layers (the ‘lean’ layers) and gradually reduce their proportion, adding more oil or medium in subsequent layers (the ‘fat’ layers). This ‘fat over lean’ principle is fundamental to stable oil painting technique.
Ventilation is paramount when using any solvents like turpentine or mineral spirits, including odorless varieties. Always work in a well-ventilated area to avoid inhaling fumes, which can have cumulative health effects. Ensure good airflow, perhaps using an open window or an air extractor fan specifically designed for studio use. Never work in a small, enclosed space without proper ventilation.
Protecting Your Masterpiece: Understanding Varnishes
Once your oil painting is thoroughly dry (and this can take months!), applying a final varnish is a critical step. Varnish serves two main purposes: protection and aesthetic unification.
Why Varnish?
A layer of varnish acts as a protective barrier between your painting and the environment. It shields the paint surface from dust, grime, smoke, and minor scratches. Critically, a good varnish should be removable. Over time, the varnish layer collects dirt. A professional conservator can remove the old, dirty varnish layer using specific solvents without harming the underlying paint, revealing the original colours. A fresh layer can then be applied, effectively cleaning and restoring the painting’s appearance. Varnish also serves to unify the final surface sheen, evening out any distracting sunken (matte) and glossy areas that may have developed during the painting process, giving the work a consistent, finished look.
Types of Varnishes
Varnishes come in different formulations and finishes:
- Dammar Varnish: A traditional natural resin varnish, dissolved in turpentine. It imparts a high gloss and saturates colours beautifully. However, dammar is known to yellow significantly over time and can become increasingly brittle and difficult to remove as it ages.
- Synthetic Varnishes: Modern varnishes often use synthetic resins like ketone or acrylic (such as MSA – Mineral Spirit Acrylic) dissolved in mineral spirits or other solvents. Examples include Gamvar (developed in collaboration with the National Gallery of Art), Soluvar, and Regalrez-based varnishes. These tend to be more stable, yellow far less than dammar, remain flexible, and are generally formulated for easier removal with milder solvents. They are the preferred choice for contemporary conservation practices.
- Finishes: Gloss, Satin, and Matte: Most varnishes are available in different sheens. Gloss varnish provides the highest shine and colour saturation. Matte varnish minimizes reflections but can sometimes lighten the darkest values slightly or make colours appear less saturated. Satin offers a compromise, a subtle sheen that is less reflective than gloss but offers more richness than matte. You can often mix gloss and matte varnishes of the same type to achieve a custom satin finish.
Retouch Varnish vs. Final Varnish
It’s important to distinguish between retouch and final varnish. Retouch varnish is a thinner dilution of varnish, designed to be applied thinly to a painting that is touch-dry but not fully cured. Its purpose is to even out the sheen temporarily, correct ‘sunken-in’ passages, and provide some protection during the extended drying period before final varnishing is possible. It does not offer the same level of protection as a final varnish and is intended to be painted over or eventually covered by a final varnish layer.
Final varnish should only be applied when the oil paint is completely oxidized and cured – typically 6 to 12 months, or even longer for very thick paint application (impasto). Applying a final varnish too early can interfere with the paint’s curing process and may cause the varnish to fuse permanently with the paint layer, making future conservation difficult or impossible.
Always wait for your oil painting to be thoroughly dry before applying a final varnish. This usually means waiting at least six months for thinner paint layers and up to a year or more for thicker applications. Varnishing too soon traps solvents and prevents the paint film from curing properly, potentially leading to wrinkling, cracking, or the varnish becoming permanently fused with the paint. Patience ensures the longevity and future conservability of your artwork.
Experimenting with different mediums and understanding the proper application of varnish are integral parts of the oil painter’s journey. These tools offer incredible control over the paint’s behaviour and the final look and preservation of your art. Don’t be afraid to try different products (always read the manufacturer’s instructions!), make test strips, and see how they affect your colours and handling. Finding the right combinations that suit your specific style and workflow can significantly enhance both the process and the outcome of your oil painting endeavours.
