There is some controversy over the use of this salt as a leather/acid buffer. The major arguments against it seem to be that it may cause a whitish discoloration to appear on the surface of the leather (potassium sulfate discoloration) and, unless applied to the flesh and grain sides of the leather, it is ineffectual. If the latter argument is correct, it would mean that leathers used for bookbinding could be treated only one time.
Potassium lactate should not be applied to powdery (red rot) leathers, nor to suede leathers, as it will result in the blackening of both. (173 , 265 , 366 )