Tengwar is the writing system used for the One Ring inscription and the Doors of Durin.
J.R.R. Tolkien created Tengwar as a script associated primarily with the Elves. The system is also called the Fëanorian script because Tolkien’s internal history attributes its creation to Fëanor. Tengwar characters can represent consonants and vowels through a structured arrangement of letters and marks.
The inscription on the One Ring is written in Tengwar, although the language of the inscription is Black Speech. This distinction matters: a script is a writing system, while a language is the spoken or written language being represented. The Doors of Durin at Moria also use Tengwar in their inscription, alongside other lettering.
Tengwar is often confused with Cirth, another Tolkien writing system. Cirth consists of angular runes and is especially associated with Dwarves, while Tengwar has the more flowing forms familiar from many Elvish inscriptions. “Angerthas” refers to an extended system of runes derived from Cirth.