Oil pastels are considered a fast medium because they are easy to paint with and convenient to carry; for this reason they are often used for sketching, but can also be used for sustained works. Because oil pastels never dry out completely, they need to be protected somehow, often by applying a special fixative to the painting or placing the painting in a sleeve and then inside a frame. There are some known durability problems: firstly, as the oil doesn't dry it keeps permeating the paper. This process degrades both the paper and the colour layer as it reduces the flexibility of the latter. A second problem is that the stearic acid makes the paper brittle. Lastly both the stearic acid and the wax will be prone to efflorescence or "wax bloom", the building-up of fatty acids and wax on the surface into an opaque white layer. This is easily made transparent again by gentle polishing with a woolen cloth; but the three effects together result in a colour and contrast layer consisting mainly of brittle stearic acid on top of brittle paper, a combination that will crumble easily. A long term concern is simple evaporation: palmitic acid is often present and half of it will have evaporated within 40 years; within 140 years half of the stearic acid will have disappeared. Impregnation of the entire art work by beeswax has been evaluated as a conservation measure.
The surface chosen for oil pastels can have a very dramatic effect on the final painting. Paper is a common surface but this medium can be used on other surfaces including wood, metal, hardboard (often known as "masonite", a defunct namebrand), canvas and glass. Many companies make papers specifically for pastels that are suitable for use with oil pastels.
Building up layers of color with the oil pastel, called layering, is a very common technique. Other techniques include underpainting and scraping down or sgraffito. Turpentine, or similar liquids such as mineral spirits, are often used as a blending tool to create a wash effect similar to some watercolor paintings.
There are a number of types of oil pastels, each of which can be classified as either scholastic, student or professional grade.
Scholastic grade, for example the Loew Cornell brand, is the lowest grade: generally the oil pastels are harder.