These inks are a part of the Keystone Formula fountain pen ink line, Birmingham's traditional dye-colorant ink. The 50mL volume will provide approximately 62 standard converter refills assuming a 0.8mL draw.
Birmingham compartmentalized their fountain pen ink recipes into four principal categories characterized by differentiating elements of the colorant component in the formula. A colorant is a dye or pigment that exhibits color. An ink vehicle is a series of chemicals used to transport colorant from storage reservoir to substrate (paper).
Keystone Formula inks are engineered using water-soluble dyes to produce a broad spectrum of colors with a variety of unique and desirable writing properties. Fitting the bill for a traditional fountain pen ink, this series by far the most popular.
Please note that Saltmarsh is one unique hue! Depending on the type of light in proximity to the ink it can change from a marshy green all the way to a light coffee brown. The ink shifts to the coffee tone in daylight, and back to the green tone in most (though not all) indoor lighting.
