Aqueous solutions of synthetic tanning agents

An aqueous solution of a synthetic tanning agent, which comprises

• (A) 5 to 60% by weight of a lithium salt of a synthetic, anionic aromatic tanning agent selected from the group consisting of (I) a condensate of sulfonated phenol or cresol and formaldehyde, (II) a naphthalenesulfonic acid/formaldehyde condensate, (III) a formaldehyde condensate of a aromatic hydroxy compound with an aralkyl halide, (IV) an urea/formaldehyde condensate of a phenol or phenolsulfonic acid, (V) a condensate of a sulfonated diaryl ether and formaldehyde, (VI) a condensate of sulfonated diphenylene or terphenylene and formaldehyde, (VII) a condensate of 4,4'-dihydroxydiphenyl sulfone and sulfonated 4,4'-dihydroxydiphenyl sulfone with formaldehyde, and (VIII) a condensate of a diaryl ether sulfonic acid and 4,4'-dihydroxydiphenyl sulfone an formaldehyde,
• (B) 0.03 to 0.50 parts weight, calculated as the metal atom of the component (B), of a water-soluble chromium, aluminum, iron or zirconium salt or a mixture thereof, per part of component (A), provided that not more than 0.375 part of chromium is present,
• (C) 0 to 60% by weight of an alkali metal salt of ethylenediaminetetraacetic acid or of a pyrophosphate, and
• water to make up 100% by weight.