Abstract

In experiments on rapid processing of pelts with paints made of sodium sulphide and caustic soda thickened with lime, good pull was achieved after 2 h with a paint at 2000 mgEq NaOH/l containing not less than 6° Be sodium sulphide (4% Na₂S). The temperature in pile was controlled by the temperature of the pelt at painting. Raising the temperature in pile (18°C was compared to 22°C) favoured wool loosening but unduly loosened the “scud” (epidermal residue left over the pelt) especially if the paint contained a high amount of caustic soda. After a 2h wool pull and liming at cool temperatures (16° was compared with 26°C falling to 23° overnight) the pelt was more mottled than the normal current production. Liming at 32°C and pH 12.5 reduced mottle to a level satisfactory for nappa leather and gave fuller feeling leather, but one of three cooperating tanners found some dull grain in leather from 2 h pull and warm liming. Liming at 32°C may be dangerously warm for works conditions: temperature not higher than 28° is recommended. The relation between the blood vessels in the skin and plumping on the one hand and, on the other, increased temperature and opening up of the fibre structure explains the development of mottle and its avoidance by warm liming.