Lim Chin Chin*, Michael Tay Ming Kiong
International Association of Forensic Sciences, 16th Triennial Meeting
August 2002, Montpellier, France, abstract No. PO-278 (poster presentation)
Objectives: This paper studies the causes of damage to two leather products subjected to different environments.
Nature of study: Tanned leather is a strong and durable material commonly used in footwear, bags, belts, straps, lanyards, wallets, pouches, holsters, whips, jackets, garments and saddles. Its strength comes from a densely woven 3-D network of strong collagen protein fibres. This study applies current knowledge on the structure and properties of leather to interpret microscopic observations, and suggests possible mechanisms for the damages.
Materials and methods: This study is based on evidence submitted in 2 recent cases. One article was a torn mouldy leather belt found on a decomposing body dumped in an equatorial forested area. The other was a torn leather bullet pouch, used and stored in a relatively dry environment. Investigators questioned whether these articles were torn or mechanically cut by a cutting instrument, and whether the damages were deliberately or accidentally caused. The methods used were stereomicroscopy, and flexing, tearing and cutting tests on control samples. Photomicrographs illustrate the observed damages and the mechanisms that created them.
Results: Damages in both leather articles were not caused by cutting instruments. The leather bullet pouch was a top grain pigment finished leather. Damages in this pouch were found to be induced by tearing of leather along a stitched seam after the stiff leather had been weakened by dessication and prolonged wear and tear. Needle holes along this stitched seam created critical failure points, and when a pulling force was applied to the leather, the extremely strong braided sewing threads acted as a cutting edge, which tore the dry brittle leather. Lab tests using a similar control leather pouch demonstrated that repeated flexing along the seam resulted in crack initiation and tear growth. The mouldy belt was found to be degraded by humidity and fungal attack, resulting in loss of tensile strength and tear resistance. A control segment of the belt was repeatedly flexed, and found to tear with the application of a twisting force by human hands. We will discuss the possible causes of damage to leather, such as water, body perspiration, pH, heat, UV, dessication and loss of oils, poor tanning, cyclical environmental changes (humidity and temperature), attacks by micro-organisms, fungi and moulds and atmospheric pollution.
Conclusion: Properly tanned leathers are extremely strong materials capable of enduring for years – even centuries; however, if poorly maintained, handled or stored, leathers are susceptible to unintended damages and can be parted and torn without the aid of external cutting instruments in a much shorter than expected time-frame.