When making a sketch or croquis, an artist places a carton—a piece of thick cardboard—under the support medium (paper) to hold it in place. In French, “carton” means cardboard.

There are two basic types of cartons used for sketches: a “single” type consisting of one sheet of processed cardboard and a “double” type comprising two sheets of cardboard. “Double” cartons are folded and hinged on one side with thread or cloth. Artists often put sketches or unused paper between the two sheets of a double carton to keep the paper clean and free of wrinkles. The strings on the edges of double cartons can also be tied together to hold the paper, making it easy to carry it. Cartons come in various sizes. The approximately 680 × 530-mm size holds charcoal paper, for example. There are also slightly smaller cartons called “medium-size” or “quarto” (560 × 400 mm) for half-size charcoal paper.

When sketching with a carton, use bulldog clips or similar items to hold the carton and paper together on all four corners. Make sure that the paper is in the center of the carton, is properly aligned both horizontally and vertically, and creates a flat, smooth drawing surface. When drawing without an easel, you can place bulldog clips on two corners of the carton, thread string through the holes in the bulldog clips, and then hang the carton around your neck to create a simple drawing board.

In addition to being a drawing board, “carton” also refers to a full-scale, paper-based rough sketch (called an “ébauche” in French) of a mural, fresco, or other large work. Some artists also use “carton” to mean a sheet of paper that acts as a support medium.

Cartons need to be handled carefully. Putting too much paper between the sheets of a carton or leaving things on top of a carton can cause the carton to warp or bend, making it difficult to use as a drawing board. Cartons are available for purchase at art supply stores and stationery stores.