Bating

1.0 Bating - Puering

1.1 Removes most of the lime
1.2 Produces a silky grain
1.3 Removes all swelling and plumping
1.4 The scud or dirt, short hairs, grease and lime soaps, dark coloured pigments, traces of epidermis are all loosened so that they can easily be removed by scudding
1.5 remains of the hypodermic tissue (flesh) are loosened so that they can be removed
1.6 Increases the degree of stretch possessed by the finished leather
1.7 Help suppleness, feel, pliability
1.8 Puering refers to dog dung
1.9 Bating refers to pigeon dung or hen dung or a substitute
1.10 Substitute is pancreatic enzyme (trypsin)
1.11 This substitution was discovered by Joseph Turney at Turney Bros. in Nottingham UK and Rohm of Rohm and Haas company, at turn of century
1.12 Small skin tanners, especially, continued to use dung into the 1950's
1.13 For pancreatic bates (now universally used) pH best is 8, temp about 100 degrees F.
1.14 Acts on reticulin, elastin and degraded protein
1.15 pH controlled by lime and ammonium salts
1.16 Some bates are pre-made to include pancreol plus NH4Cl, plus wood flour
1.17 The wood flour content can leave a brown deposit
1.18 Pancreol can be bought separately and the ammonium chloride added
1.19 The amount of bating done with shoe upper leathers is decreasing
1.20 Upper leather bating is done to soften and open up the grain, so it follows a surface delime only
1.21 Calf skins are difficult. The smaller the skins the more so. Too much bate gives loose flanks, but too little gives cracks as a result of lack of opening up
1.22 Goat skins are tough, and given a longish bate
1.23 Wool sheep have a fairly open structure and are given a shortish bate
1.24 Bate and delime are sometimes put together to give just sufficient bating to ensure clean and supple grain
1.25 Mechanical agitation helps loosening and removing the scud and fat.
1.26 Ration of skins to water 1:4. This allows skins to open up and float without washing
1.27 Bated pelts are slippery, non elastic, flaccid
1.28 Bated goods are very reactive
1.29 Scudding is done about this stage
1.30 Skin tanners used to check for a well bated skin by seeing if it would go through a wedding ring

2.0 Drenching

2.1 Treatment of bated pelts with an infusion of bran or flour or its equivalent
2.2 To continue and complete the removal of lime (which was largely done in bating)
2.3 To swell the pelt slightly, separating fibres into fibrils
2.4 To cleanse and free the grain entirely from scud and thus produce an absolutely clear white pelt
2.5 Frowned upon as an uncontrollable process
2.6 Enzymes in bran produce organic acids
2.7 CO2 also produced as bubbles of gas within the skin, causing the skin to float
2.8 This floating is called rise, and indicates that a certain amount of acid production. Sometimes done 2 or 3 times
2.9 These bubbles help separate the fibres
2.10 Organic acids neutralise any lime
2.11 Safer than bran drenching is adjustment of pH by addition of weak organic acids (lactic, acetic)
2.12 If pH is required below 4.3 salt is used to prevent swelling
2.13 If skins are tanned while swollen leather comes out hard and sometimes brittle
2.14 Uneven swelling distorts, weakens the fibre structure
2.15 Gases produced are hydrogen (45%), Nitrogen (26%), Carbon dioxide (25%) and oxygen (2%)
2.16 Acids produced are lactic (77%), acetic (19%), formic (3%), and butyric (1%)
2.17 These acids dissolve the remaining lime
2.18 The particles of bran cleanse the skin, absorbing dirt and grease
2.19 Sometimes done instead of pickling, giving stock a mildly acid reaction before tanning