Shrinking Temperature of Leather

The change of area is tested by exposing the leather to boiling water. A so-called "boiling test" is performed
at the end of tannage for wet chrome-tanned leathers. Dry leathers are first soaked in water at 20 ± 2 °C for one hour.
Determinarion afthe degree af shrinkage:
Leather samples of exactly 10 x 10 em are prepared and the outlines drawn on paper or preferably on graph paper. Then the leather sample is immersed in boiling \vater for exactly 1 minute and after shon draining placed onto the paper with the previously drawn outlines. The loss of area compared to the original sample is determined by plainmetering. It is indicated as % degree of shrinkage.

This test determines the temperatures at which leather begins to shrink under the action of damp heat.

Shrinkinge temperatures and types of tannage:
 Chrome leather                                       90-100 °C
 Vegetably/synthaically tanned leather       70-85   C
 Aluminium/iron !ealher                             70-80  °C
 Aldehyde leather                                     75-85   C
 Chamois leather                                      65-70   C
 Alum/Glace leather                                  70-75   C


The resistance of leather to higher temperatures varies considerably depending on the type of tannage.
Damage caused by shrinkage is irreversible in most cases.In vegetably tanned leathers.temperature exceeding
45 degree C may darken the tanning color and impair distension of grain up even before shrinkage.

 Determination of The shrinking temperature
  A strip of length 50 mm is cut Out to be tested, If the leather is max. 3 , strip is 3 mm wide, if the
  thickness exceeds 3 mm the strip is 2 mm wide. Two small punched into the ends of the strip. hooks. 350 ± 10 ml of warm. distill water filled into a 500 ml glass vessel (inside diameter 70 ± 2 mm), and the vessel is placed (80~IOO watt output) which heat slowly by 2. °C per minute. The vertical thermometer with a measuring range  50 - 105°C (maximum deviation circular dial with pointer and a rigid which a thread is led. To tighten the thread a 3 g weight is fixed to the outer end and the strip of  leather to the other end. A magnectic stirrer is connected to heat the water evenly. When the leather clearly starts to get warped or to shorten the temperature is read off and is indicated as «shrinking temper-Jture".