CUERDA SECA, OR DECORATING WITH BLACK LINES
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We often have customers ask what they can use to outline shapes in black, then fill in the broad areas with color. Sometimes this technique is referred to as Cuerda Seca, which you can read more about below.
Here are several ways to do this.
Using a slip trailing bottle, draw lines with Black Wax Resist. The wax repels the glaze which you then apply to the colored areas. When the wax burns out a black line is left behind. Note: If you have a glaze that flows a lot, it still may cover the black line because the wax will burn out before the glaze starts to flow. To apply the colored glaze sections, some people use a brush and others use a slip trailing bottle to apply it in a puddle.
Using a slip trailing bottle, draw lines with engobe. Engobes have a chemical formula in-between a slip and a glaze. Because they are clay based like a slip, they have stiffness. Therefore, they can be applied thick and raised up off the surface, and will stay that way. Because Engobes have some flux like a glaze, they have some sheen without having to be covered with a clear glaze. Examples are: Spectrum Raised Accent Colors, Duncan French Dimensions, and Laguna Engobes.
The same technique as #2, but using slip. You can purchase ready made slip, or apply colorants to slip made from your clay body. If the slip is mixed thickly enough, it will make a barrier to the colored glaze areas, so you can fill them easily. This method will leave a dry surface, or can be covered with a clear glaze. Ready made slips include Potter's Slip. Colorants include stains, oxides, or colored underglazes such as the Duncan EZ strokes which are highly pigmented.
You can also apply the lines using a slip trailing bottle and a black glaze. Depending on the glaze and your firing temperature, the glazes may move and the line may not be crisp. But some people really like wavy this effect. In fact the product often referred to as Cuerda Seca often has this.
Apply the colored glaze first, then scrape it off where you want your line to be. Fill the line with slip, engobe, another glaze, etc.
Sometimes syringes are used instead of slip trailing bottles.
If you do a lot of line drawing, the AirPen is the perfect tool. It ensures smooth lines with no sputtering and globs.
About Cuerda Seca...
The Cuerda Seca technique derived from the Spanish/ Moorish technique which used animal fat and grease and mineral pigments such as iron or manganese. A brief description of that technique is : A linear design is first applied to the bisqued clay surface. The design may be applied freehand by brush, painting lines with a mixture of manganese and oil as the medium. Nowadays mineral oil is generally used, or wax resist is substituted for the manganese oil mixture. With tile, the design was often traced via carbon paper onto the bisqued clay surface. Then, with the manganese/ oil mixture, lines were painted onto the surface, following the carbon paper lines. The design could also be silk screened onto the bisque, using a paste-like mixture of manganese / oil medium or other workable wax/oil medium Glazes were generally inlaid with bulb syringes into the areas between the lines, occasionally brushes were used to pool or float in glaze to an area. Malibu used rubber bulb syringes, with different sized tips.
The manganese /oil or wax resist lines serve to keep the different glazes separated. With the manganese /oil technique, the oil burns out and the manganese imparts a dark line onto the clay. The effect is likened to a glazed 'stain glass' or cloisonné effect. I suppose health concerns about use of manganese can easily be addressed by subbing materials.
A companion technique to cuerda seca is the Cuenca method, where raised ridges in the clay, instead of wax or oil resist lines serve to separate the different glaze colors. (Thanks to Stephanie Stephenson for this explanation of Cuerda Seca)