Understanding Oil Painting Mediums
Oil painting mediums can be somewhat of a mystery. What do they do? Cold-Pressed or Refined? What’s the difference between them all?
If you are content to live with variable drying rates, sinking in and all the vagaries of ‘raw’ oil paint, then there is no reason whatsoever to encumber yourself with mediums. However, if you aspire to recreate some of the classic effects of the past — such as those in the work of Turner or Rembrandt — you will need to modify your oil paint, as they did, with oil painting mediums.
What do mediums do? Painting mediums offer more than just extending oil colours from the tube. They modify the working properties by making oil colours either more fluid (for expressive mark making) or stiffer (for dense impasto work) in consistency. Mediums also shorten or extend the drying time of your painting and depending upon which on you use, they can achieve a variety of different sheens.
Most mediums are produced by combining a limited amount of ingredients. Once you understand these you are equipped with the knowledge to predict how any combination of them will work.
Oils with solvents
Drying oils such as linseed, poppy and walnut will oxidise into a translucent glossy film over time, giving oil paint it’s characteristic richness, luster an depth. Unlike solvents, oils increase the drying time of paints, and improve the overall adhesion and appearance. However, excess use of oils will not only substantially increase the drying time, but can cause the paint film to wrinkle. A comprise is to mix oil with solvents — often called ‘Van Eyck’ medium; a simple 1:1 oil/solvent mixture.
Waxes
Wax is commonly added in small amounts to paint as a stabiliser, but used in larger amounts it creates a textured impasto effect that tries quickly to a matt finish. Wax has been used for centuries to create softly luminous effects when painted thinly. A thin final coat of cold wax makes a wonderful matting agent, allowing paintings to be hung in difficult light. Wax is both brittle and easy to melt, limiting its use to rigid panels unless it is combined with another ingredient.
Resins
Painters have long used tree resins dissolved in turpentine (a varnish) to add both gloss to the paint and decrease drying time. Historically, all manner of resins were used — amber, dammar, gum arabic or mastic, for example — but most have fallen by the wayside as they proved unstable in the long term, causing the paint film to yellow, peel or crack. Despite these known defects, resins add such amazing and subtle effects to oil paints that they continue to be used. A modern synthetic resin known as alkyd promised to solve these defects, allowing painters to recreate effects similar to Turner, without the fading and cracking that afflicts his work.
Solvents
A solvent is a thinner such as turpentine or white spirit. Solvents significantly decrease drying time, but weaken and dull the paint film, making them ideal for imprimatura (stained ground) or other initial painting stages. Excess use of solvents will cause lack of adhesion or ‘chalking’, however, they often have unpleasant fumes. Solvents are also a key ingredient in resinous mediums. They can be used to rapidly underpaint oils and then be worked over in a matter of minutes. Solvents applied to upper layers of oils can create interesting effects. A low-odour solvent, such as Gamsol or Sansodor, will make this safer and more pleasant but extend the drying time.
Top Tip: Cold-Pressed or Refined?
Even though they are taken from the same seed, Cold-Pressed Linseed Oil is rather different to Refined Linseed Oil.
Cold-Pressed is extracted without heat, which means a good quality oil is extracted from the seed, but in smaller quantities. This means that it is a better quality oil , and should be used if you make your own pigments.
Refined Linseed Oil has been manufactured through a process using heat and alkali to extract the oil, which gets more oil out of the seed, but sometimes also brings some of the seed with it. It therefore goes through a refining process. It’s slightly cheaper than Cold-Pressed but still of a very good quality, making it the ideal medium if you’re simply mixing it with paint.
Feel free to contact me if you have any queries regarding oil painting. Connect with me on all socials @rhymesandoils
