Alkyd Mediums

You can use oil paint straight from the tube or dilute it with thinners. However, you can also experiment with drying oils, resins, waxes, and diluents to alter the characteristics of your tube color. Most manufacturers offer several types of medium that can improve the flow of paint, provide a satin or gloss finish and speed up or retard the drying time of oil paint. Last week, I explained how drying oils work as binders and as mediums. This week, we’ll take a look at Alkyd mediums.

Composition of Alkyd Mediums

Alkyd mediums are made up of resins produced by a reaction of natural oil with a poly-functional alcohol and poly-basic acid.

There are two ways of introducing an alkyd into your painting. The first and most common is the use of an alkyd medium. Alkyd painting mediums are popular because they are made with milder solvents and speed the drying time of oil colors. Liquin and Galkyd are the best-known alkyd mediums. M. Graham also makes a walnut oil-based alkyd, which is the glossiest followed by the Galkyd, with the Liquin having a more satin finish. Liquin and Galkyd contain lead, which speeds up the drying time, but can be toxic in a closed setting. For this reason, you should only use alkyd resins in an open area with good ventilation.

Benefits of Using Alkyd Mediums

Thin layers of oil colors mixed with alkyd resin painting medium will dry in twenty-four hours and make very tough, yet flexible paint films. Alkyd-based painting mediums can also add gloss and transparency to paint layers and help prevent drying in, which is when the darks in a painting lose their gloss and look matte compared to other parts of the picture. Good for layering, alkyd mediums can be used for very complex glazing applications. Drying time can be extended by adding a few drops of linseed oil. Mineral spirits can be used for thinning. 

Thick Vs. Thin Alkyds

Alkyds are available in a variety of properties, including thinning, thickening, glossy finish, matte finish, fast drying time, slow drying time and come in fluids or gels. Fluids can be obtained in both fast or slow-drying, high viscosity (thicker, can show brush marks), or low viscosity (great for washes). Gels are thicker than the high viscosity fluids, and can be used to show pronounced brush marks in the paint film and will not turn into a fluid as they are worked. Gels also come in various viscosities aimed principally at the painters who want to develop more impasto in their work.

Alkyd Paint

The second means of introducing alkyd into a painting is the use alkyd paints. There are several available, including Da Vinci, C.A.S., Gamblin, Grumbacher, and Windsor & Newton. Note: As a binder, alkyd resin cannot hold as high a pigment load as linseed oil. Alkyds can be mixed with regular oils and are reduced with the same solvents. To speed up the drying time of regular oils, you can substitute a few of your most frequently used oil colors for alkyd colors, such as white and ultramarine blue. Because these colors are used in so many mixtures, it speeds up the overall drying time of all colors.

Some Cautions

For optimal adhesion, alkyd mediums should not be used over the top of traditional oil painting mediums or unmodified, slow-drying paint. Regular oil paint can be layered over alkyds, but it is not recommended that alkyds be layered over oil, as the less flexible alkyd film may crack. Adding an alkyd resin will make a color layer fatter, while adding solvent will make a color layer leaner. Therefore, only the lower layers should contain solvent and the upper layers should contain increasing amounts of alkyd medium.

Conclusion

Alkyd resins can change the look and feel of your paint. Some artists don’t use any alkyd resins, claiming that they dilute the color intensity and lack the "jewel like" look of oil paint. While alkyds are a very durable material, they can become brittle with age and must be used judiciously by the artist. It’s worth experimenting with alkyd resins, especially when it’s important to speed up drying time. Just be careful to use them safely, correctly and sparingly.

Note on Comparing Food Grade to Artist Grade Oil

Last week, I forgot to mention that it’s best to use products that are made and sold for art production. An artist friend pointed this out to me and I thought I would pass this on. You should always use artist grade dryer oils when painting, since they have a longer shelf life than food grade oil, are of superior quality and there’s less of a chance of them going rancid. Artist’s linseed oil’s long shelf life is due to Alkali refinement (a ‘washing’ process) that removes most of the free fatty acids, mucilage and other impurities that can lead to rapid spoilage. How prone a particular oil is to going rancid is due to fatty acid composition. Flax oil has a shorter shelf life than safflower oil, due to higher percentage of fatty acids. Drying oils are mostly made up of unsaturated fatty acids (e.g. linolenic and linoleic acids). These fatty acids are the components that produce an “off” smell through oxidation, and also what makes oil paint dry.