Fig. 3

a One half of the cocoon (horizontal cut, average length 5.0 cm) showing the inner (smooth) and the outer (coarse) surface morphology. b SEM image: the outer surface of the cocoon exhibiting the rough morphology. The particulate covering the surface of the silk fibers. c A high resolution SEM image of the outer surface of the cocoon showing the uneven texture due to the presence of crystals of different sizes. d At higher resolution SEM image cuboidal shaped crystals were irregularly stacked over one another. Dimension of the cuboidal crystals: the crystals were of approximately 1–2 μ in length and 1–2 μ in breadth. e The SEM image of the inner surface of the cocoon exhibits a smooth texture with intertwined silk fibers crisscross’ the surface. f It shows the inner surface between the fibers with irregular gaps with few particulates. There were very few crystals found in the inner surface of the cocoon. g SEM image of the outer surface of the cocoon after the calcium oxalate monohydrate layer has been leached out. The outer surface of the cocoon showing smooth texture after removal of the calcium oxalate monohydrate crystals. h Outer surface of the treated cocoon at a high resolution SEM image showing the spots where calcium oxalate monohydrate crystals were embedded in the native cocoon prior to leaching. i SEM image of the inner surface of the cocoon after leaching away of the calcium oxalate monohydrate from the outer surface. As noticed earlier in the untreated cocoon, the SEM image of the inner surface of the cocoon exhibits a smooth texture with intertwined silk fibers criss-crossing the surface