Oil pastels are small sticks of pigment mixed with oil and a wax binding element. They are more or less shaped like crayons but are much softer and easier to blend. Oil pastels were created in Japan to allow school students to spend more time drawing freely and creatively with colors and less time tediously copying writing characters in black ink. Oil pastels were a cheaper alternative to chalk pastels and oil paints. Although popular among artists for their versatility, oil pastels do have some drawbacks.
Oil pastels are soft and are therefore more fragile than other handheld art media like hard pastels, crayons or colored pencils. It's very easy to snap an oil pastel in half if you press too hard on it. However, if you don’t vary the pressure on the pastel, the range of effects you can get with it are quite limited.
Oil pastels are more expensive than crayons or colored pencils. Artists often have to purchase them in entire sets, which makes simply replacing one or two as you use them up difficult. You can buy individual pastels in better art shops and online, but the expense sometimes equals that of simply buying another entire cheap set. Also, you tend to use up an entire stick of oil pastel much more quickly than a colored pencil or a tube of paint.
This is both an advantage and a disadvantage. Oil pastels can be blended, which allows artists to make new colors and create effects. However, this can make them difficult to work with. Many artists find oil pastels too messy. They often smudge their work accidentally, or get oil pastel all over their hands and papers. When you're using dark colors, smearing can make it more difficult to add lighter colors without blending them together. Leaving backgrounds clean is almost impossible, so you will always have to fill in your backgrounds with color so your drawings don't look dirty. Additionally, you must apply a varnish to each drawing or it will become smeared beyond recognition. There are special brands of oil pastel varnish, but you can also use watercolor fixative spray.
Loss of Precision
Oil pastels generally cannot be used as sharply and precisely as paint or pencils. The lines in oil pastels will almost always be soft and blurry, making fine details difficult without using a knife or some other medium. It’s impossible to maintain a sharp point on an oil pastel, especially since the finer and higher-quality oil pastels are even softer than the less expensive ones.