Pigments for Art and Industry
What Is a Pigment Exactly?
A pigment is an insoluble, non-reactive coloring solid material that is usually suspended into a liquid binder. Pigments are usually prepared into finely divided powder state to aid in dispersal and even application on solid surfaces. They must not dissolve in the binder or solvent and not chemically react with binder or solvent. If a colorant dissolves in a solvent to form a clear colored solution, then the color is classified as a dye.
Mineral and Natural Earth Pigments
Perhaps the oldest pigments available are the mineral natural earth pigments. These are pigments that occur naturally and are merely collected, cleaned, ground to a finely divided powder and suspended in a medium like fat, oil, egg whites or natural resin. The natural mineral pigments are iron oxides, ochres, and beige, natural clays impregnated by iron oxides and related metal oxides. The colors are not usually deep or saturated and consist mainly of beige, brown, brownish-red, black, green, grey, and yellow. Being mostly inorganic, these pigments are opaque and easily dispersed.
Synthetic Inorganic and Mineral Pigments
One of the first synthetic inorganic pigments were used in ancient Egypt. Egyptian blue is a calcium copper silicate colorant that was made from the high-temperature fusion of sand, lime and copper ore. Later, the wonderful red vermilion was synthesized from sulfur and mercury by alchemists searching for the philosophers stone.
By the 19th century, the rapidly growing field of chemistry had yielded a whole new collection of vibrant permanent pigment colors to add to the artists' palette. The cadmium reds, yellows, and oranges, cobalt blues, violets and greens and chromium pigments like viridian(hydrated chromium oxide) and chrome yellow(lead chromate). This was the industrial revolution which brought about the mass production of premixed paints not only to industry but also artists and craft people.
Synthetic Organic Pigments
During the 20th century, two world wars and new forms of transportation propelled the world into a much faster pace of technological advancements. The development of the internal combustion engine created a new need for petroleum feed-stocks. Not only was petroleum an invaluable energy source, it quickly proved to be the main source of many organic chemical feed-stocks for the industry. The pigment industry is no exception. Many of the colors were discovered by accident while scientists were trying to create other chemical products. Colorants such as pthalo blues and greens, the quinacridone reds and violets, the arylide yellows, and aniline colors. Many of these colors show varying degrees of transparency, have vivid or intense colors, and high tinting strength. What this means is the ability to be added to a paint binder in a far lower concentration. Of coarse, organic pigments are generally hydrophobic and more difficult to disperse. They usually require higher amounts of wetting and dispersing agents to get them into water based coatings.
A pigment that has recently seen widespread popularity in many craft circles is mica pigment. Based on a natural flake silicate mineral, these pigments come in an unlimited array of colors and special effects. Due to mica"s tendency to opalescent and Interference(think oil on water here) properties, they dazzle any surface they cover. Many automotive finishes are based on mica nowadays because they are both cheaper and less toxic than traditional synthetic pigments. Also, as an added bonus, most mica pigments are fade resistant unless light-sensitive dyes are used as additives.
Other properties that make mica a favorable colorant is that they are chemically inert hence blend with just about any coating medium. They can add sparkling iridescence to a finish with just a small amount added. Their unique particle shape allows them to be easily dispersed in both water and solvent based paints without forming agglomerates.
Universal Tints and Pigment Dispersions
Another useful way to color paint mediums and resins is using pigment in liquid form. The commons form is universal tints. A universal tint is called that because they can be used in virtually any finish or medium as a colorant. They typically consist of a very finely ground solid pigment, a surfactant, emulsifiers like glycols, and water. These mixtures are ground in pigments dispersion machinery until a smooth even color mix is obtained. Typically, these tints are used at 5% concentration to paint medium or less. For deep colors, up to 10% is used. Using 15% or higher concentration would affect the drying and curing characteristics of the paint finish or resin.
Aqueous pigment dispersions are usually offered from specialty art suppliers. These are used for water-based acrylic artist mediums to created custom colors or paints with varying tint strengths.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2019 Jason