Literally meaning “flow”, a flux is a liquid in which some solid substances melt at a lower temperature than their usual melting point. To some materials, a certain liquid may act as a good flux while it isn’t for others. Temperature and pressure are two factors of great influence. Water, at normal pressure and temperature, acts as a flux for sugar but doesn’t for gold. In relation to jewelry, it is used to aid goldsmiths with soldering and to dissolve the chemicals needed to create some types of synthetic gemstones. It is also used in similar conditions as a medium to heat, diffusion treat, and (glass) fill gemstones.