tannage

Tannage is the process of converting raw animal hides or skins into stable leather that resists decomposition and water damage. It involves treating collagen proteins with tanning agents to cross-link fibers, increasing strength, durability, and dimensional stability. The choice of tanning agent determines the leather’s properties, appearance, and feel.

The principal tanning methods are vegetable tanning and chromium tanning. Vegetable tanning uses natural tannins extracted from bark, leaves, or fruit, producing firm, long-lasting leather with a characteristic patina that develops with use. Chrome tanning employs chromium(III) salts to rapidly stabilize hides, yielding softer, more flexible leather with high heat resistance. Other methods include aldehyde tanning, oil or fat tanning, and alum tanning, each producing distinct textures and performance traits.

The tanning process typically follows several stages. Skin preparation includes soaking, liming to remove hair and degrade proteins, fleshing, and degreasing. This is followed by bating, deliming, and sometimes pickling to adjust pH. The actual tanning step introduces the tanning agents and cross-links the collagen. After tanning, retanning, fatliquoring to restore suppleness, dyeing, and finishing treatments are applied to achieve the desired color, texture, and water resistance.

Historically, tanning dates to ancient civilizations and evolved significantly with industrialization. Vegetable tanning dominated in many regions for centuries, while the introduction of chrome tanning in the late 19th century revolutionized production by increasing speed and yield.

Environmental and regulatory considerations focus on effluents and chemical handling. Chrome tanning requires careful wastewater management due to chromium compounds, whereas vegetable tanning is often viewed as more environmentally friendly, though it can be slower and more capital-intensive.