This charm is an example of water etching. The technique is fun, easy, and can be used to create different levels of depth in a work.
The technique is done by drawing a design on a dry clay piece. Then, using nail polish, the areas that are to be raised are painted. The polish acts as a resist. It is a good idea to paint the back of the piece too as it can get water on it. The edges can be painted to create a raised effect or left unpainted to recede. Since this process removes clay, the original clay piece should be made several cards thicker to make sure it doesn't get too thin. When the polish is dry, take a damp sponge and begin wiping across the surface of the piece. Rinse the sponge and repeat until the desired depth is reached. (Be sure to save the dirty rinse water..... there's silver in there!) Texture can be added to the recessed areas (while they are still wet) with a stencil brush, using a stippling effect.