Didymium

For the amoeboid species see Didymium wildpretii.

Didymium (Greek:twin element) is a mixture of the elements praseodymium and neodymium. It is used in safety glasses for glassblowing and blacksmithing, especially when a gas (propane) powered forge is used, where it provides a filter which selectively blocks the yellowish light at 589 nm emitted by the hot sodium in the glass, without having a detrimental effect on general vision, unlike dark welder's glasses. The strong infrared light emitted by the superheated forge gases and insulation lining the forge walls is also blocked thereby saving the crafters' eyes from serious cumulative damage such as Glassblower's cataract. The usefulness of didymium glass for eye protection of this sort was discovered by Sir William Crookes.