From the suede type leather sample no bloodstain particles were lost. After applying a blood droplet a visible blood stain was left at the surface of the leather, but most of the blood seemed to be absorbed by the fibrillated leather structure.
From artificial leather large blood flakes were obtained (Fig. 2G). Although these surfaces are considered to be smooth, the uneven surface structure of this material is reflected in the particles showing darker shades in welled areas.
Somewhat larger but more cracked flakes, which show deep lines, were shed from bloodstains on human GW786034 (Fig. 2H). At the opposite, small and fragmented particles without any structural detail were lost from blood that had dried on a fingertip.
When a droplet of blood is deposited on a substrate, it may stay on the surface or penetrate into the structure. This depends largely on the nature of the substrate and its wettability and imbibition characteristics .
On non-porous substrates blood cannot penetrate (no imbibition). The wettability of the substrate determines the initial shape of the droplet (as well as the ultimate shape of the stain). During the desiccation stage a depressed central part and a thicker corona are formed due to the gelation process. For larger stains (diameter over 4.5 mm) radial crack formation occurs in the corona, the number of cracks being higher for bigger stains  and . The size of the scale-like plaques pilus result from crack formation depends on the drying conditions. Slow drying under high relative humidity leads to larger plaques . Eventually these plaques can be lost in a process called delamination or flaking  and .