Creating Visual Effects With Specks
Specks can also be used to add the third dimension of height or depth to coatings in a controlled manner. They can be used to create a hobbed look or, conversely, to create indents in the finished glaze surface. Combining a soft glaze in sized color speck form with a harder glaze coating can produce interesting glaze effects, especially on vertical surfaces. Sized color specks can be used to simulate iron spots in brick and quarry tile surfaces and can also be used to produce the popular “enamelware” coating on whiteware bodies. They can also be used to produce unusual effects depending on the coating composition.
Using sized color specks, there is almost no limit to the number of designs that can be created.
Where Can Specks Be Used?Sized color specks can be used anywhere an enhanced glaze effect is desired, but they are most commonly used on ceramic tile and structural clay products. They can either be specified directly from a supplier and incorporated into a company’s own glaze formulation, or can be found in many off-the-shelf glazes from hobby glaze manufacturers. Using sized color specks adds a new dimension to a company’s existing product line and can enhance marketing appeal.
What Types of Specks Are Available?Sized color specks are available in just about every color and formulation imaginable. While specks have been used for centuries to add visual interest to otherwise mundane ceramic surfaces, new speck formulations and combinations are making today’s ceramic products even more exciting and easier to sell.
Pebbles and Dents. Pebbles are hard specks that retain their size and remain above the glazed surface after firing rather than melting down in the glaze, resulting in a hobbed look. Dents, on the other hand, are much softer than the glaze in which they are fired and create visually appealing depressions in the finished glaze surface.
Reactive Specks. Reactive specks are based on soft fluxes and contain materials such as titanium dioxide, fluorspar, various phosphates, rutile, copper oxide/carbonates, iron oxides and manganese. These materials often react in unpredictable ways in different glaze compositions to produce unique effects. In some cases the specks may blossom out into “fingers” or crystals that spread into the glaze. However, determining how the specks will react is largely a matter of trial and error since the formula of both the specks and the glazes in which they are used is often proprietary. Companies that want to use reactive specks will need to be willing to spend time testing them in their glazes before using them in production.
Staining Specks. Most color specks are sized through at least two screens—a coarse screen and a fine screen—to eliminate specks that are either very large or very small. Some color specks, however, are sized through just one screen, such as 60 or 80 mesh, leaving the very fine particles in the mix. These fine particles act like stains within the glaze, coloring and tinting it to a color that is similar to the specks. The larger specks in the mix then stand out as more intense shades of the same color.
Transparent Specks. Transparent specks are specks that become transparent when fired. They can be used with matte glazes to create a “magnifying glass” effect. The specks melt out but remain shiny in the glaze, enhancing or magnifying the color and adding a sparkle to the final product.
Color Blends. Several different colors of specks can be blended together and used in the same glaze to create yet another visual effect. For instance, a combination of black, cobalt blue and white specks can create a “denim” look, and that formulation can be altered even further by using very few blue specks to create a “stonewashed denim” look. Blending different brown specks can produce a “tweed” look, while blending metallic colors can produce a “gunmetal” effect. While some of these color blends can be obtained from the speck supplier, manufacturers can also experiment to achieve their own unique effects.
Black Specks. While far from unusual or new, black specks are often incorporated into tile glazes where they offer a secondary benefit—the ability to ship virtually 100% of the product manufactured. When manufacturing plain glazed tiles, one piece of dust or kiln dirt in the glaze will cause the tile to be thrown into the “seconds” category. Black specks, however, hide such small imperfections, enabling tile manufacturers to maximize their profitability as well as their design.
How Do I Spec Specks?Speck sizes range from 4 to 200 mesh in very soft to very hard formulations and a variety of colors. Ceramic manufacturers or decorators simply need to determine the effect they’re hoping to achieve, and then select the specks accordingly. Speck suppliers are typically willing to send out several samples to allow the manufacturer or decorator to test the specks before purchasing a large quantity. Specks that produce effects that are close but not exactly what the manufacturer or decorator had in mind can often be adjusted to meet the company’s needs.
Are There Any Formulation or Firing Considerations?Sized color specks are available to work with almost any glaze formulation, so if one color speck doesn’t work, another one probably will. However, companies unfamiliar with using color specks may encounter several problems when trying to incorporate them into their glazes.
One common challenge is getting the larger, heavier color specks to remain suspended in the glaze. While organically bonded specks tend to resist settling, sintered specks often sink to the bottom of the glaze. The specific gravity of the glaze can be adjusted to compensate for this problem. When working with dipping glazes, the glaze must be continuously agitated to keep the specks in suspension.
Finely sized (80 mesh or smaller) or staining specks can be difficult to disperse in the glaze slurry. Adding small amounts of dispersants (such as liquid dishwashing detergent) will eliminate surface friction, allowing the specks to repel each other and disperse throughout the glaze.
To avoid grinding the specks below their specified size, specks should not be added to the glaze slurry until all necessary particle size reduction of the glaze has been completed. At that point, they can be gently blunged into the glaze to achieve the desired effect.
Another common problem occurs when the color specks don’t produce the anticipated effects after firing. Finely sized specks may disappear in a soft, high-fire glaze, while hard or more refractory speck compositions may not melt and could result in a coarse or rough fired surface. Specks should be specified for the specific firing process and glaze being used to ensure the best results.