White leather may be produced by alum or formaldehyde. The latter gives much more water-resistant leather. The combination of formaldehyde with collagen, hair or silk in unbuffered and buffered solutions has been studied. Less formaldehyde is taken up by silk than by hair or collagen. With all three, greater fixation occurs at high pH values. The presence of the salts studied has little effect on fixation of formaldehyde on silk, increases it on collagen, and decreases it on hair. Formaldehyde tanning is thought to involve its combination with the free amino and imino groups, and the sulphydril groups of keratins. Results suggest that formaldehyde tanning is best done at pH values between 8 and 10. Buffered solutions control pH, and salts help to prevent cracky grains.