Ink
Ink in the UPDV is named in two registers: as the literal medium by which a scribe records dictated prophecy, and as a foil to the deeper writing the New Testament preachers prefer.
The Scribe's Tool
Ink first surfaces in the account of Baruch's work for Jeremiah. When the officials questioned him after the scroll's reading, his answer made the practical detail explicit: "He pronounced all these words to me with his mouth, and I wrote them with ink in the book" (Jer 36:18). The scroll exists because a prophet spoke and a scribe wrote, with ink as the visible carrier of the words.
Letters In Place Of Visits
In the Johannine letters, ink is the thing the writer is content to leave behind once a face-to-face visit becomes possible. "Having many things to write to you⁺, I would not [write them] with paper and ink: but I hope to come to you⁺, and to speak face to face, that our joy may be made full" (2John 1:12). The same posture closes the third letter: "I had many things to write to you, but I am unwilling to write [them] to you with ink and pen" (3John 1:13). Ink is adequate for the message, but presence is preferred for the joy.
Spirit Instead Of Ink
Paul takes the figure further. The Corinthians themselves are the letter, and the medium is not ink: "being made manifest that you⁺ are a letter of Christ, served by us, not written with ink, but with the Spirit of the living God; not in tables of stone, but in tables [that are] hearts of flesh" (2Cor 3:3). The contrast pairs ink with stone on one side and the Spirit with hearts of flesh on the other; the ordinary writing tools name the limit that the new covenant exceeds.