The invention relates to a formulation for use in chrome or chrome-free tannage. Said formulation comprises a clay mineral, which after 30 minutes of intense stirring in water at 50 °C has an average particle diameter of less than 2 µm, or a bimodal size distribution consisting of a first fine-particle fraction, whose average particle diameter is less than 0.5 µm and a second coarser fraction, whose average particle diameter is less than 5 µm, said values being defined according to the ISO 13320-1 determination method by means of combined laser light diffraction and light diffusion, the proportion of the first fine-particle fraction lying between 10 and 90 wt. %. The formulation also comprises one or more substances from one or more of the following groups: organic polymers, aldehyde tanning agents, sulphone tanning agents, resin tanning agents, phenol tanning agents, stuffing agents, vegetable tanning agents, colorants and pigments.
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