Mordant in the context of Colloidal

Etching is traditionally the process of using strong acid or mordant to cut into the unprotected parts of a metal surface to create a design in intaglio (incised) in the metal. In modern manufacturing, other chemicals may be used on other types of material. As a method of printmaking, it is, along with engraving, the most important technique for old master prints, and remains in wide use today. In a number of modern variants such as microfabrication etching and photochemical milling, it is a crucial technique in modern technology, including circuit boards.

In traditional pure etching, a metal plate (usually of copper, zinc or steel) is covered with a waxy ground which is resistant to acid. The artist then scratches off the ground with a pointed etching needle where the artist wants a line to appear in the finished piece, exposing the bare metal. The échoppe, a tool with a slanted oval section, is also used for "swelling" lines. The plate is then dipped in a bath of acid, known as the mordant (French for "biting") or etchant, or has acid washed over it. The acid "bites" into the metal (it undergoes a redox reaction) to a depth depending on time and acid strength, leaving behind the drawing (as carved into the wax) on the metal plate. The remaining ground is then cleaned off the plate. For first and renewed uses the plate is inked in any chosen non-corrosive ink all over and the surface ink drained and wiped clean, leaving ink in the etched forms.

A dye is a colored substance that chemically bonds to the material to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and may require a mordant to improve the fastness of the dye on the fiber.

The majority of natural dyes are derived from non-animal sources such as roots, berries, bark, leaves, wood, fungi and lichens. However, due to large-scale demand and technological improvements, most dyes used in the modern world are synthetically produced from substances such as petrochemicals. Some are extracted from insects and/or minerals.

Sizing or size is a substance that is applied to, or incorporated into, other materials—especially papers and textiles—to act as a protective filler or glaze. Sizing is used in papermaking and textile manufacturing to change the absorption and wear characteristics of those materials.

Sizing is used for oil-based surface preparation for gilding (sometimes called mordant in this context). It is used by painters and artists to prepare paper and textile surfaces for some art techniques. Sizing is used in photography to increase the sharpness of a print, to change the glossiness of a print, or for other purposes depending on the type of paper and printing technique.

Natural dyes are dyes or colorants derived from plants, invertebrates, or minerals. The majority of natural dyes are vegetable dyes from plant sources—roots, berries, bark, leaves, and wood—and other biological sources such as fungi.

Archaeologists have found evidence of textile dyeing dating back to the Neolithic period. In China, dyeing with plants, barks and insects has been traced back more than 5,000 years. The essential process of dyeing changed little over time. Typically, the dye material is put in a pot of water and heated to extract the dye compounds into solution with the water. Then the textiles to be dyed are added to the pot, and held at heat until the desired color is achieved. Textile fibre may be dyed before spinning or weaving ("dyed in the wool"), after spinning ("yarn-dyed") or after weaving ("piece-dyed"). Many natural dyes require the use of substances called mordants to bind the dye to the textile fibres. Mordants (from Latin mordere 'to bite') are metal salts that can form a stable molecular coordination complex with both natural dyes and natural fibres. Historically, the most common mordants were alum (potassium aluminum sulfate—a metal salt of aluminum) and iron (ferrous sulfate). Many other metal salt mordants were also used, but are seldom used now due to modern research evidence of their extreme toxicity either to human health, ecological health, or both. These include salts of metals such as chrome, copper, tin, lead, and others. In addition, a number of non-metal salt substances can be used to assist with the molecular bonding of natural dyes to natural fibres—either on their own, or in combination with metal salt mordants—including tannin from oak galls and a range of other plants/plant parts, "pseudo-tannins", such as plant-derived oxalic acid, and ammonia from stale urine. Plants that bio-accumulate aluminum have also been used. Some mordants, and some dyes themselves, produce strong odors, and large-scale dyeworks were often isolated in their own districts.

Mordant red 19 is an organic compound with the chemical formula C₁₆H₁₃ClN₄O₅S. It is classified as an azo dye.

It is a mordant used in textile dyeing, usually in combination with chromium. It is usually found as the sodium salt.