Black Gold

HP Black Ink 56: 19mL¹, $34.87². Density approx. that of water, 1g/mL.

The density of gold is approx 19g/mL.

Price of gold: $46.15 /g

Price of HP#56: $34.87/(19mL * 1g/mL) ~= $2/g

30mL bottle of Pelikan 4001 Fountain Pen Ink: $10.95

1L bottle of Pelikan 4001 Fountain Pen Ink: €30 ~ $43

Pelikan 4001 by weight: $10.95 / (30mL * 1g/mL) = $0.37/g

Pelikan 4001 by weight: $43 / (1L * 1kg / L) = $0.04/g