TANNINS FOR LEATHER

Leather is a durable and flexible material made from the skin or hide of animals (commonly cattle, goats, sheep, pigs, buffalo, deer, and exotic animals like alligator or ostrich).

• Purpose of tanning: Fresh hides contain proteins (mainly collagen) that are prone to decay. Tanning stabilizes the collagen fibers, making the leather resistant to decomposition, flexible, and long-lasting.

• Types of leather (based on tanning process):

1. Vegetable-tanned leather (uses plant tannins)
2. Chrome-tanned leather (uses chromium salts) 
3. Aldehyde-tanned leather (uses glutaraldehyde/formaldehyde) 
4. Combination-tanned leather (mix of vegetable and chrome methods)

Tannins are central to vegetable tanning, one of the oldest and most traditional leather-making methods.

• Tannins bind to collagen fibers in hides via hydrogen bonding and hydrophobic interactions. 
• This crosslinking stabilizes the protein structure, preventing microbial attack and decay. 
• Tannins make the leather more rigid initially, but it becomes supple with use.

 Vegetable-tanned leather is popular for luxury goods, craft leatherwork, belts, saddles, and heritage footwear. In sustainable fashion, vegetable tanning is gaining market share as consumers demand metal-free leather.

Vegetable tanning uses plant materials rich in polyphenolic tannins:

• Bark: Oak, chestnut, hemlock, mimosa (Acacia mearnsii) 
• Wood: Quebracho, mangrove 
• Leaves: Sumac 
• Fruits & pods: Tara pods (Caesalpinia spinosa) 
• Other sources: Myrobalan, valonia

 PROS: 

• Biodegradable and eco-friendly (no heavy metals) 
• Ages beautifully with a natural patina 
• Firm, good for tooling and carving
   

CONS: 

• Stiffer initially, sensitive to water 
• Longer processing time 
• Less color variety compared to chrome-tanning