They found Burns, who was known to make his own ink, used stale beer, carbonised elephant tusk, lard and sulphuric acid as the main ingredients in an ink known as “Ivory Black’, although the quality of the various components shifted slightly over time as his fortunes rose and then declined.
https://www.thedrinksbusiness.com/2018/07/robert-burns-used-stale-beer-to-make-his-ink/
> They found Burns, who was known to make his own ink, used stale beer, carbonised elephant tusk, lard and sulphuric acid as the main ingredients in an ink known as “Ivory Black’, although the quality of the various components shifted slightly over time as his fortunes rose and then declined.
https://www.thedrinksbusiness.com/2018/07/robert-burns-used-stale-beer-to-make-his-ink/