An opacifier is a substance added to a material in order to make the ensuing system opaque

Opacity (optics)

Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

. An example of a chemical opacifier is tin dioxide

Tin dioxide

Tin dioxide is the inorganic compound with the formula SnO2. The mineral form of SnO2 is called cassiterite, and this is the main ore of tin. With many other names , this oxide of tin is the most important raw material in tin chemistry...

 (SnO₂), which is used to opacify ceramic glaze

Ceramic glaze

Glaze is a layer or coating of a vitreous substance which has been fired to fuse to a ceramic object to color, decorate, strengthen or waterproof it.-Use:...

s and milk glass

Milk glass

Milk glass is an opaque or translucent, milky white or colored glass, blown or pressed into a wide variety of shapes.First made in Venice in the 16th century, colors include blue, pink, yellow, brown, black, and the white that led to its popular name....

; bone ash

Bone ash

Bone ash is the white, powdery ash left from the burning of bones. It is primarily composed of calcium phosphate. It is commonly used in fertilizers, polishing compounds, and in making ceramics...

 is also used.

Opacifiers must have a refractive index

Refractive index

In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

 (RI) substantially different from the system. Conversely, clarity may be achieved in a system by choosing components with very similar refractive indices.

Opacifiers must also form small particles in the system. Opacifiers are generally inert

Inert

-Chemistry:In chemistry, the term inert is used to describe a substance that is not chemically reactive.The noble gases were previously known as inert gases because of their perceived lack of participation in any chemical reactions...

.

Sometimes opacifiers are added to medical implants to make them visible under X-ray

X-ray

X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...

 imaging. This is especially true in the case of most polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

s which are often unrecognizable in the body when viewed using X-rays.

In solid rocket propellants and some translucent smokeless powder

Smokeless powder

Smokeless powder is the name given to a number of propellants used in firearms and artillery which produce negligible smoke when fired, unlike the older gunpowder which they replaced...

s, the primary method of heat transfer into the propellant grain from the combustion process is by radiation, and opacifiers such as "lamp black" may be added to the propellant mixture to ensure the heat does not penetrate far below the surface of the grain, which could cause detonation. The opacifiers also prevent sub-surface overheating and localized premature ignition in the grains where imperfections absorbing the thermal radiation are present. Carbon black

Carbon black

Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...

 is commonly used for this purpose; other possible additives are nigrosin

Nigrosin

Nigrosin is a mixture of synthetic black dyes made by heating a mixture of nitrobenzene, aniline and aniline hydrochloride in the presence of a copper or iron catalyst. Its main industrial uses are as a colorant for lacquers and varnishes and in marker-pen inks...

, Prussian blue

Prussian blue

Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....

, methylene blue

Methylene blue

Methylene blue is a heterocyclic aromatic chemical compound with the molecular formula C16H18N3SCl. It has many uses in a range of different fields, such as biology and chemistry. At room temperature it appears as a solid, odorless, dark green powder, that yields a blue solution when dissolved in...

, etc. in amounts ranging commonly between 0.1-0.5%.