Abstract

Experimental lime-sulphide treatment has been assessed from the fibre structure of the pickled pelt ( after fixing it in fornialin + salt) com pared with that from “normal” processing:— soaking, liming, deliming, bating and pickling, or soaking, painting, liming, deliming, bating and pickling. Ease of unhairing and removal of epidermis have also been considered. The investigation included experiments on the influence of temperature, composition of the lime liquor, alkaline baths subsequent to painting, duration of piling in paint and composition of the paint.

Unhairing and epidermis removal are shown to be two different processes under the conditions of lime-sulphide treatment, in which un hairing is only removal of hair shaft leaving the root and a short length of shaft within the grain layer. The paint, penetrating from the flesh, appeared to have passed the root, both bulb and club types, as well as newly initiated hair papillae, and begun attack on the hair at the level of the sebaceous gland. Breakdown of the hair shaft can extend both inwards toards the root and outwards along the free hair shaft: the hair cuticle was more resistant than the internal structure. Readily visible damage to the free hair shaft was caused by high amount of water in the paint or high amount of sulphide in the presence of high amount of water.

The “normal” paint used in the experiment was approximately 08 g Na2S+ 5 g lime + 7 g water to 100 g pelt, and at the end of piling for 24 hours belly unhaired readily but butt did not. With this paint, increased time in pile did not improve the degree of unhairing, nor did 218 raised temperature which did however, improve the removal of epidermis. Liming after painting completed unhairing and removal of epidermis, but it seems possible that caustic soda after painting might have an adverse effect on unhairing if this has not at least begun at the end of piling. Caustic soda in the paint did not improve unhairing, but where the hair was loose the renioval of epidermis was seen to be easier than in its absence.

Painting opened up fibre bundles but did not open up the weave pattern, in contrast to liming or to painting followed by liming, after which fuller fibre bundles and less compactly interweaving pattern occurred. Increasing sodium sulphde in the paint increased splitting up and, especially when the pelt was piled at raised temperature, led to separa tion and a damaged appearance of the fibre structure. Caustic soda in a lime-sulphide paint, increased the fullness of the fibre bundles. Raised temperature had a marked effect in opening up the structure, particularly of the belly, which, at room temperature, usually appeared little opened up.

Immersion and movement in lime liquor containing a low concentra lion of sodium sulphide satisfactorily unhaired the pelt, and, especially at raised temperature, opened up the fibre structure.