Ceramic Color Pigments

Ceramic color pigments are inorganic compounds that contain chromophore ions and impart color to inorganic solids such as ceramic wares. They are widely used as coloring agents for ceramic glazes and bodies.

They possess high thermal stability and are chemically stable to the phases formed during firing of glazed or body products. They also provide chemical resistance to ceramic substrates.

Color and intensity

Ceramic color pigments, often referred to as ceramic stains, open up a whole new realm of color possibilities for potters. They are typically formulated as a calcined powder system that expands the potter’s palette and creates an infinite variety of ceramic colors in clay bodies, inglazes, underglazes, and onglazes.

They can also be mixed with metallic oxides to obtain a wide range of consistent colors. Many of these colors are soluble and toxic, so they must be stabilized by combining with metals or salts to produce colorants that will not fume or volatilize in the glazes or enamels they are used to decorate.

Some of the most common colorants in ceramics include copper, iron, and cobalt. The first two are usually available in synthetic forms that contain 5-15% impurities, whereas cobalt can be found as a naturally occurring mineral (magnetitite).

In addition to being widely used in porcelain and other glazed ceramics, copper is also very useful as a colorant in glass-ceramics such as glassware, tableware, and drinking vessels. It is used in alkaline lead and barium high-fired glazes to provide a wide range of blue-green colors, ranging from the darkest green to turquoise.

Another common colorant is iron, which is found in a number of natural clay bodies and can also be added to a glazed clay body or glaze. The color it imparts varies depending on the oxidation and reduction rates of the fire in which the clay is fired.

When a clay body contains iron, it is generally colored to a grayish or brownish hue. This is the result of the interaction between iron and oxygen, which results in an oxidized form of iron (rust) when exposed to the air.

To turn rust back into clean iron, we need to reduce it by exposing it to the air or adding another substance to the rust (oxides). In the case of ceramics, this can be achieved through a variety of processes such as acidifying the clay or using different firing conditions in the glaze or enamel.

Traditionally, black iron oxide was the most commonly used ceramic colorant. It has a high iron content and is easily prepared in the form of a powder by grinding or heat processing the mineral magnetite. It is then calcined at a temperature to yield a solid black pigment that is very effective for coloring enamels and glazes, ordinarily from 3 to 5% of the overall composition.

Stability

Ceramic pigments are inorganic color pigments formulated for ceramic glaze stains, porcelain glass and vitreous enamels. They are characterized by high resistance to thermal deformation and degradation. They can resist to processing temperatures up to 1300degC without altering the colors of their components. They are widely used in glass bottle, colored glass, stained glass, ceramics glaze and ceramic glazed objects.

The coloring properties of these pigments depend on the chemical composition and the granulometric size of their crystal structures. Some are very stable (rutile, spinel and zircon), while others are more soluble and dissolve in the glaze during cooling. This can result in a reduced color intensity or a different shade of the same pigment.

These pigments are usually formulated with water-swellable smectite clay. Depending on the desired color intensity and the final application of these pigments, the quantity of the smectite clay needed may vary from 1% to 10%.

For example, smectite clay is used in conjunction with titanium dioxide and chrome oxide green to give an orange tint to glass bottles and colored glass. It is also used with iron oxide red to give a blue tint to stained glass.

Another important characteristic of ceramic color pigments these pigments is their resistance to oxidation and corrosion. They are resistant to ozone, acid rain, strong acids and other corrosive agents commonly found in industrialized areas. They are also non-migrating and non-bleeding.

CICPs are the most stable inorganic pigments. Their color properties are excellent when they are applied in glaze stains, porcelain glass and vitreous glazes production. CICPs are very versatile and can be used in many other substances including silicone, latex, glass paint and ceramic paint, glass ink and ceramic ink, paper, rubber, laminates and co-extrusions, window profiles, wood grain laminate and decking.

In order to study the influence of temperature on the stability of these pigments, a ternary mixture of granite sludge (GS), marble sludge (MS) and electroplating sludge (ES) was prepared, as shown in Table 1. After homogenization by wet ball milling, these pigments were fired at a temperature of 1100degC for 30 min and at 575degC for 2 dwells.

Dispersion

Ceramic color pigments are used to add color to a variety of materials, including paint and coatings, thermoset composites, inks, plastics and textiles. They also are used for specialized applications, such as decorative and industrial coatings and automotive interiors and exteriors.

Most color pigments come from a combination of natural and synthetic sources. These can include both mineral and metal pigments. These can vary in the chemical stability of their molecules, as well as the particle size distribution.

Particle size is essential to the optical behavior of a pigment and its colorant stability, both of which are critical for achieving an optimal color and appearance in a glazed ceramic product. The particles must be fine enough to produce a diffuse reflection and to maximize the colorant’s coating power while maintaining chemical stability at the same time.

Inorganic ceramic pigments are formulated to meet these requirements, and they typically have particles in the range of 2 microns or smaller. This is because smaller particles can dissolve in a molten glaze and can cause the color to fade or change.

The pigments are then grinded in a ball mill to form a fine powder. The grinding process can be carried out wet or dry.

This process is used to produce various kinds of ceramics, such as porcelain and vitreous enamel. The resulting powder is then sprayed onto a refractory substrate and fired to form a colored glaze. The glazed surface is then protected by a hard, durable, chemically inert glaze that is easy to clean and wash.

During the ball milling process, a mixture of glass raw material (frit), a ceramic clay and inorganic pigments is mixed and dispersed with water. This produces a dispersion that can be added to the raw material glaze composition and then mixed with it during firing.

This technique produces a pigment that is more stable than the usual oxides that are found in glazes. The dispersion is also more resistant to fuming and volatilization in a kiln, preventing the colorant from changing its appearance during the firing process. It is also much less toxic ceramic color pigments than standard oxides, which can be harmful to the health of ceramic artists and the environment during production.

Pigmentation

Ceramic color pigments are inorganic coloring agents that contain chromophore ions and impart color to inorganic solids such as ceramic wares and glass. They are used as coloring agents for ceramic glazes and bodies, coatings, and inks. They have high thermal stability and refractoriness, which enable them to be used for a wide range of end-use applications.

The crystalline structure of these pigments is determined by the type of raw material used during their production process. The synthesis of these pigments involves various steps such as mixing, calcining, grinding and washing. These processes influence the pigment’s coloring power, tonality and chemical resistance.

These pigments are manufactured by combining various wastes from different industrial sectors. The sludge from electroplating (ES–rich in Cr and Ni), the sludge from the marble sawing (MS–rich in CaCO3) and the sludge from the granite sawing (GS–rich in SiO2) were combined to prepare the pigments.

ES, MS and GS were mixed in different weight proportions, such as ES:MS:GS (50:50, 25:75 and 75:25) and GS:MS:ES (30:20:50). The mixture was homogenized and fired to a maximum temperature of 1100 degC and a cooling rate of 5 degC/min until 550 degC.

The prepared waste based-inorganic pigments exhibited good coloring hue and tinting power when added to a transparent and bright lead-free glaze (TB) [SiO2 (51-53 wt.%); Al2O3 (41-43 wt.%); ZrO2 (7-9 wt.%); P2O5 (1-3 wt.%)] and an opaque matt glaze (OM) [SiO2 (54-56 wt.%); Al2O3 (20-22 wt.%); CaO (10-12 wt.%); K2O (3-5 wt.%); Na2O (3-5 wt.%); MgO (2-4 wt.%)]. The color was evaluated by adding the pigment to a standard ceramic body and evaluating it with a colorimeter.

The obtained pigments are thermally stable and exhibit good tinting power, originating nicely colored and defect-free ceramic materials. They are also capable of achieving a wide range of shades. In addition, they are environmentally friendly and have an economic value due to the absence of virgin raw materials. The studied waste-based-inorganic pigments complied with the requirements of CIE* a* b* coordinates and are therefore suitable for ceramic applications.