Endorsed by the Oil Pastel Association of America. Each stick offers uniformity of color distribution and handles evenly and cleanly without stickness; with the feel of a fine chalk pastel. These are easy to handle and blend and may be applied to almost any surface. They are used extensively over acrylic and oil color. Holbein oil pastels will not readily break or crumble. Because of the wax content and use of highly refined mineral oil they will never harden completely eliminating the drying out and cracking that can be seen in pastels that use vegetable oil. Great performance without health risk; Holbein oil pastels are rated as requiring no health label according to the ASTM health standards. The manufacturer recommends that no attempt be made to fix the surface but suggests mounting under glass.