I was able to get something bolder by using the uppercase delta glyph. But it isn't perfect.
-Greg % - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - % \version "2.22" embiggenChordNames = #(define-scheme-function (size) (number?) #{ \with { chordNameFunction = #(lambda (in-pitches bass inversion context) (define exemptions (list musicglyph-markup)) (define (helper mu) (if (list? mu) (if (memq (car mu) exemptions) (markup (#:fontsize (- size) mu)) (map helper mu)) mu)) (let ((orig (ignatzek-chord-names in-pitches bass inversion context))) (markup (#:fontsize size (helper orig))))) } #} ) \paper { ragged-last = ##f } \layout { indent = #0 \context { \ChordNames \embiggenChordNames #2.5 } \override ChordName #'font-name = #"Open Sans Soft Cd SemiBd" \override Staff.BarLine.hair-thickness = #4 \override Staff.BarLine.thick-thickness = #8 } IntroChords = \chordmode { \time 6/8 \set majorSevenSymbol = \markup { Δ } \set minorChordModifier = \markup { − } a2.:m7 c2.:maj7 des2. f2.:dim a2.:m6 e2.:aug a2.:m eis2.:7 } << \new ChordNames \with { \override BarLine.bar-extent = #'(-1 . 3.5) \consists "Bar_engraver" } \IntroChords >> % - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - %