The Bleeding of Inks in High Humidities.

Some pigments used in printing inks have a sufficiently high water solubility that they bleed when exposed to atmospheres of high humidity. Under these conditions, halftones printed with them will change color and when the printed picture is a color proof, it may be impossible for the printer to match it. A test has been developed which permits the estimation of the degree of bleed for any printing ink. It is made by printing a light halftone (5%) on the paper selected for the printed job, exposing this sheet to an atmosphere of 100% relative humidity at room temperature for 16 hours. Bleeding is indicated by a deepening of the color. The color change is measured by instrument.