Oil tanning:
Chamois leather is produced by oil tanning. Characteristics of oil tanned leather:
- Fat/ Oil containing with unsaturated carbon linkage.
- Contain the soft & silky property
- Doesn't become hard.
- Shrinkage temperature is 70°c.
- Wets back rapidly.
- Cream yellow color.
- Orthopedic purpose.
Principle of oil tanning:
- The pelt is prepared to open & plump up the fibre structure by good liming & later delimed well. In some cases grain side are shaved-off after pre-liming treatment of HCHO.
- The pelt is treated with about 25-30% of its weight of cod/fish oil & drumming for 6 to 8 hours to break open the fibre structure & to allow oil to penetrate inside the pelt to combine well.
- On the application of oil, as water in oil emulsion is formed & slowly water content of pelt is reduced & oil penetrates into the pelt.
- After the application of oil the pelts are hang up in hot & humid temperature. Auto oxidation & typical aldehyde odour noticed.
- The period of auto-oxidation is 2 to 3 weeks forming various oxidation products (e.g: acronaldehyde, crotonaldehyde, peroxide) assist in tanning. The end point or completion of tanning is determined by yellow color.
Characteristics of oil:
- Contains minimum 18-20 no of carbon in which unsaturated may 8-10
- Acid value is low. (Below 5)
- Iodine value is high (120-180)
- Shouldn't be rancid.
- Usually fish oil/Cod oil.
- Fish oil is preferable for actually blown.