A formulation and process for making a formulation for leather tanning using highly complexed Chrome III salts coupled with polymer complexing agents of medium and low molecular weight in the range of 500 to 10,000. Complexing polymers can contain vinylic acid/ester co-polymers, polyamine/polyamide co-polymers and polymers condensed from saturated carbon linked aromatic groups based on phenol and naphthalene sulfonates or other aromatic rings.