Didymium 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 blocks the yellowish light emitted by the hot sodium in the glass, without having a detrimental effect on general vision, unlike dark welder's glasses. Blocked also, is the strong ultraviolet light emitted by the superheated forge gasses and insulation lining the forge walls thereby saving the crafters' eyes from serious cumulative damage. (See also arc eye, also known as welder's flash or photokeratitis.) General Name, Symbol, Number praseodymium, Pr, 59 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance grayish white Atomic mass 140. ... General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Atomic mass 144. ... Eye protection refers to protective clothing for the eyes, which comes in many types depending upon the threat that is to be reduced. ... Sculpting hot blown glass. ... A blacksmith is an artisan specializing in the hand-wrought manufacture of metal objects, such as wrought iron gates, grills and railings, light fixtures and furniture, sculpture, weapons, decorative and religous items, cooking utensils and tools. ... Propane is a three-carbon alkane, normally a gas, but compressible to a liquid that is transportable. ... A blacksmiths forge For finery forges (making iron) see finery forge. ... Coloured and Neutral Density filters An optical filter is a device which selectively transmits light having certain properties (often, a particular range of wavelengths, that is, range of colours of light, or polarizations), while blocking the remainder. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... UV redirects here. ... Arc eye, also known as arc flash, welders flash, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by welders who have failed to use adequate eye protection. ... Arc eye, also known as arc flash, welders flash, corneal flash burns, or flash burns, is a painful ocular condition sometimes experienced by welders who have failed to use adequate eye protection. ... Arc eye is a painful condition sometimes experienced by welders who have failed to use adequate eye protection. ...

Didymium photographic filters are often used to enhance fall scenery by making leaves appear more vibrant. This is accomplished via the the special properties of the substance which causes the removal of part of the orange region of the color spectrum. When present, this group of colors tends to make certain elements of a picture appear "muddy". In photography, a filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. ...

Didymium is also used in calibration materials.

Didymium (Gr. "twin element") was discovered by Carl Mosander in 1841 and was so named because it is very similar to lanthanum, with which it was found. Mosander wrongly believed didymium to be an element, under the impression that "ceria" (sometimes called cerite) isolated by Jöns Jakob Berzelius in 1803 was really a mixture of cerium, lanthanum and didymium. He was right about lanthanum being an element, but not about didymium. Mosander did as well as could be expected at the time, since spectroscopy had not yet been invented. His three "elements" accounted for at least 95% of the rare earths in the original cerite from Bastnaes, Sweden. Mosander may have named "didymium" with a bit of tongue-in-cheek: an allusion to the fact that his four children had been born as pairs of twins! Didymium had not been difficult to find, since it was providing the pinkish tinge to the salts of 1803 ceria when in trivalent form. The real tour de force was to find the colorless lanthanum in the mixture! During the period when didymium was believed to be an element, the symbol Di was used for it. Carl Gustaf Mosander (Kalmar 10 September 1797 – Lovö, Stockholm County 15 October Swedish chemist. ... 1841 is a common year starting on Friday (link will take you to calendar). ... General Name, Symbol, Number lanthanum, La, 57 Chemical series lanthanides Group, Period, Block 3, 6, f Appearance silvery white Atomic mass 138. ... The periodic table of the chemical elements A chemical element, or element for short, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. ... Jöns Jakob Berzelius Statue of Berzelius in the centre of Berzelii Park, Stockholm Jöns Jakob Berzelius (August 20, 1779 - August 7, 1848) was a Swedish chemist. ... 1803 was a common year starting on Saturday (see link for calendar). ... General Name, Symbol, Number cerium, Ce, 58 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Atomic mass 140. ... General Name, Symbol, Number lanthanum, La, 57 Chemical series lanthanides Group, Period, Block 3, 6, f Appearance silvery white Atomic mass 138. ...

In 1885 Carl Auer von Welsbach discovered that didymium was really a mixture of the elements praseodymium and neodymium, and effected the separation by a fractional crystallization of the double ammonium nitrates from nitric acid. He wanted to name his two elements "praseodidymium" and "neodidymium" ("green didymium" and "new didymium", respectively), but a syllable was soon dropped from each. The "didymium" name lived on in untruncated version, in part due to the use in glassblower's goggles. 1885 (MDCCCLXXXV) is a common year starting on Thursday of the Gregorian calendar (or a common year starting on Saturday of the 12-day slower Julian calendar). ... Carl Auer von Welsbach ( 9 September 1858 - 8 April 1929) was an Austrian scientist and inventor who had a talent for not only discovering advances, but turning them into commercially successful products. ... General Name, Symbol, Number praseodymium, Pr, 59 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance grayish white Atomic mass 140. ... General Name, Symbol, Number neodymium, Nd, 60 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white, yellowish tinge Atomic mass 144. ...

During World War I, didymium glass was reputedly used to send Morse Code across the battlefields. Didymium did not absorb enough light to make the variation in lamp intensity obvious, but anyone with binoculars attached to a prism could see the absorption bands flash on or off.

The name lived on also in the rare earth industry. In the USA, commercial "didymium" salts were what remained after cerium was removed from the natural abundance mixture obtained from monazite, and thus contained lanthanum as well as Mosander's "didymium". A typical composition might have been 46% La, 34% Nd, 11% Pr, remainder mostly Sm and Gd, for material extracted from South African "rock" monazite (from Steenkampskraal). European usage was closer to the Mosander composition. Such cerium-depleted light lanthanide mixtures have been widely used to make petroleum-cracking catalysts. The actual ratio of praseodymium to neodymium varies somewhat depending on the source, but is often around 1:3. Neodymium always dominates, which is why it got the "neo" appelation, being responsible for most of the color of the old "element" in its salts. Typically, in ores, neodymium is higher in relative abundance in monazite, as compared to the bastnaesite compositions, and the difference is noticeable when unseparated mixtures derived from each are examined side-by-side: the monazite-derived products are more pinkish, and the bastnaesite-derived products are more brownish in tinge, due to the latter's increased relative praseodymium content. (The original cerite from Bastnaes has a rare earth composition highly similar to that of monazite sand.) In the late 1920's Leo Moser recombined praseodymium and neodymium in a 1:1 ratio to create his "Heliolite" glass, which has color-changing properties between amber, reddish, and green depending on the light source. [One can only hope that an appropriate intermediate fraction of the Pr-Nd separation might have been used, to save some expense, since at the time, separated praseodymium and neodymium oxides were the most costly glass colorants in use.]

Recently, it was found that praseodymium could be included in the neodymium-iron-boron magnet composition without excessive sacrifice in magnetic strength. This has the effect of "stretching" the neodymium supply, while simultaneously finding a home for the under-utilized praseodymium. For such magnets, the appropriate mixture can be prepared directly by solvent extraction without purifying either component separately. Maybe we should soon be calling them "didymium-iron-boron" magnets!