Tortoiseshelling

Genuine tortoiseshell was used in the Eastern hemisphere at one point to adorn boxes, wall panels, and other items. Introduced to Europe, tortoiseshell became popular in the seventeenth century, and Europeans began to appreciate tortoiseshell's distinctive coloring and markings. Now that real tortoiseshell is not commonly used, a tortoiseshell finish can be achieved with paint — either oil- or water-based.

Tortoiseshelling is one painting technique that is striking but can be extremely overwhelming if covering a large surface. It is generally a better idea to use a tortoiseshell finish as a trim or accent on walls, instead of over the entire wall. Tortoiseshelling the individual panels on doors can also provide a pleasing effect, especially when used in conjunction with ivory or cream-colored paint.

To perform oil-based tortoiseshelling, you should first apply an undercoat of a solid color that provides a good base for the tortoiseshell effect, such as a rich cream or yellow color. Next, apply an oak varnish — either light or dark — with a stiff, flat varnishing brush. Work diagonally across the area to be painted from one top corner down. While the varnish is still wet, brush it into a zig-zagged series of bands in different widths. When working on wood, you should thin the varnish, but on plaster walls, use unthinned varnish.

Next, soak a rag in paint thinner and use this to soften the edges of the painted bands. Paint on a diluted raw umber paint, again in a zig-zag pattern. Do the same with a burnt umber paint in the middle of the raw umber. Soften the whole surface by using a dry brush to work the edges until you are happy with the effect.

Tortoiseshelling can also be performed with water-based paints, but usually on a smaller scale. For this, you need to start with a gesso base and apply a coat of terracotta paint, which can be made of two parts burnt umber, two parts light red, one part titanium white and one part yellow ochre, mixed into white latex paint. After this is applied, mix a glaze using one part light red and one part burnt umber and coat the terracotta base, adding a little bit of ivory black to create a mottled effect. Use a dry brush to soften the edges, and apply another glaze using a very little bit of cadmium yellow.

Of course, the tortoiseshell approach can be used with other colors as well, to create a mottled effect that, while not resembling actual tortoiseshell, can be quite interesting. If you are using water-based paints for tortoiseshelling, you should apply a satin varnish to give depth to the process.