Carbon Ink That Stays in the Bottle and on the Page: Pigment Loading, Opacity and Settling Time for a Low-Cost Writing and Printing Ink

This paper addresses a practical question in viscosity: a serviceable black ink can be made almost anywhere from carbon pigment, water, a binder and a preservative, and recipes circulate freely. Using a self-contained computation from stated assumptions, the study evaluates the options across the range a small operation ordinarily meets and identifies the point at which the balance of cost, quality and material use changes. The headline findings are that lowest loading meeting od 1p2 is 6; od at that loading is 1.2; settling days at that loading is 113; od at 20g is 1.83; settling days at 20g is 28. These figures come from a simulation study: the work is SIMULATED, NOT MEASURED, no physical trials were performed, and every number reported is taken from the deposited computation output so that any reader can reproduce or refute it with local values. The practical value of the result is a rule that can be applied at the point of work without further calculation, together with the tabulated cases from which the rule was derived and a statement of the assumptions on which it depends. Where the computation shows that a widely used practice wastes money or material, that finding is stated directly; where it shows that a popular economy is genuine, the size of the genuine saving is stated with equal directness, so that effort can be directed to the economies that are worth having.