A Study of the Afterchrome Process

Abstract

The following aspects of the afterchrome process have been examined‐1. The dyeing of afterchrome dyes prior to chroming2. The effect of dichromates on wool during afterchroming3. The effect of dichromates on chrome dyes during afterchroming.The main difference between chrome dyes and acid dyes of comparable constitution is the greater sensitivity of the former to precipitation by acid. Several of the more commonly used chrome dyes are out of solution under normal dyeing conditions, and yet have excellent level‐dyeing properties.The rate of uptake of chromium by wool during afterchroming is independent of the presence of dye on the wool. When afterchroming at the boil, the pH of the liquor rises steadily, owing to the reduction of chromic acid to neutral tervalent chromium compounds, but this effect is much less marked at 80° and 90°c. The rate of absorption of chromium is very sensitive to the pH of the chroming bath, but is only slightly affected by temperature.During afterchroming at low pH values, there is a tendency for certain dyes to be destroyed by oxidation. The chrome lakes formed by afterchroming with dichromates have much better wet fastness than those formed by aftertreatment with salts of tervalent chromium.