A hydrophilic colloid is hardened with a vinyl-sulfone hardener in the presence of a borate compound in an amount sufficient to accelerate the rate of hardening. The borate compound is preferably a compound of Formula (I), or a salt, hydrate or precursor thereof: B(L).sub.n (I) wherein each L is independently --OH, --OR, --NH, --NR, or a substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, or substituted or unsubstituted heterocyclic group; R is a substituted or unsubstituted alkyl group or substituted or unsubstituted aryl group; and, n is 1, 2, or 3, with the proviso that at least one L is --OH. Preferred borate compounds are sodium and potassium borate, and hydrates thereof, and phenyl boronic acid.