A painting medium is an oily liquid that you use to adjust the body of the oil paint. It can thin the paint, make it dry faster or slower, or make the paint transparent or matte in appearance. It can even thicken the paint to the consistency of cake icing! The most common type of medium for oil paint is what the paint already has in it — linseed oil. The following premade mediums are commonly available:
- Standard: A standard medium is a mixture of materials, usually turpentine, linseed or other oils, and a resin. Each of these materials adds a characteristic to the medium, whether it's to aid in the drying, to provide a durable finish, or to keep the painting flexible on the canvas. You can find various types of mediums in stores from the same suppliers that make your paints.
- Drying: Some mediums speed drying of the painting; sometimes the painting will dry overnight. These mediums have the addition of driers that are tested for stability of the finished painting. Use care when you use these mediums. If a painting dries too rapidly, it may crack or develop fine hairline cracks over time.
- Glazing: You can use a glazing medium to create transparent layers of color. The mixture is also fast drying to allow repeated buildup of layers of glaze. You can apply a glaze to a painting in several ways.
- Impasto: Impasto is a way of painting in thick layers. You can apply the paint itself in a thick manner or you can use an impasto medium or gel. Add the impasto medium to the paint on your palette to create a thick, buttery mixture. Impasto mediums use either natural or synthetic oils and resins to give the paint a thick body.
- Alkyds: Several companies make painting mediums with synthetic resins known as alkyds. These mediums are very fast drying. Mediums made with alkyd synthetic resins were invented in the last 50 years and now come in a variety of consistencies from thin to thick impasto mixtures.