Reducing vein marks in hides during processing

Vein marks are very difficult to get rid of completely but can be minimised by taking special care in the process operations. Pronounced veininess is caused due to inherent problems in the feeding/starvation of cattle and so on. Due to the marks, the collagen fibre structure in that particular area is permanently changed. There are two types of vein marks appearing in leather. One is a convex vein, which only appears when the blood is left in the vein and is very unusual. The other type are concave veins and these are the type that normally appear. This is the topic of discussion which we will deal within this paper. The appearance of veins is often related to factors not controllable in the beamhouse operations. These include, breed, gender and age of the animal, nutrition, use of hormones, method of slaughtering, the way the hide is handled, how it is cured, and the storage and transportation methods employed before processing. Efforts towards minimising vein marks in the beamhouse with enzymes have shown results but they have a tendency to reduce the total hide substance. The vein depth is still visible though, even after the enzyme treatment and even though the marks may not be visible during finishing. They do become pronounced after lasting if you make shoe uppers. So vein marked wet-blue that would be OK to make bag and other softee leathers and also printed leathers are not suitable for shoe upper or glazed finished leathers. A relatively better solution would be to reduce the vein marks in the liming operation, using high quality sodium sulfide along with sodium hydrosulfide (iron content less than 10 ppm) in flaked form. Similarly the use of pure hydrated lime powder instead of poor quality slaked lime lumps are also considered as a factor, because the separation of the individual fibre is important. In the bating operation, there would be scope for minimising the vein mark with high quality bating agents such as Oropon G type mild bates, which are based on modified pancreatic enzymes along with a protease enzyme. The pancreatic enzyme has been obtained from pig pancreas, which can operate a degradation process of non-collagenous, globular proteins in the fibre structure. It is important that the removal of residual protein and scud from the grain by enzymes is done during bating. But to ensure a proper bating action it is essential to maintain the temperature of 37°C in the process bath. Enzymes are a biological catalyst, which enable specific organic substances to be degraded. In leather processing such characteristics are being used very selectively. For example, a protease enzyme has a high degree of selectivity in removing unwanted proteins remaining inside the fibre structure, while leaving collagen fibres undamaged. So, specific enzyme treatments, even after making wet-blue leather, would be helpful to reduce vein marks and a perfect removal of growth marks. A technique could be applied in the retanning process, which is based on the system to tighten the grain (Magnopol FTP) and lubricate the vein structure (Chromopol V) and then further retanning which could include Sellatan HO, a mellow flexible replacement syntan, to further tighten the grain structure. The use of Sellatan LV allows the dyes to penetrate through to the flesh side and not from the grain as it usually is and so reduces the visibility of the vein marks. They can be further minimised by applying a resin finish. Leathers of softer types and normal resin finishing would be ok while glazed finishes should be avoided. To sum up, to avoid making the vein mark problem worse, we suggest the following ideas: * keep uncontrolled protolytic effects to the minimum by adding preservatives in rawhide preservation if using sea salt as main curing element * get rid of as much bacteria as possible by washing using enough of the correct bactericide in the soaking process * short soak with controlled not too high temperature * reducing the temperature in liming. Try to equalise the state of the hides as quickly as possible, preferably in the presoak. Use only 0.2% of soda ash in the soak; regulate the pH by using additives * avoid very strong liming * reduce time of liming Reducing the amount of lime is desirable but it is important to achieve sufficient opening-up; this can be done by raising the alkalinity with caustic soda; or use of Erhavit DMC; reduce the amount of lime or the liming time even more. The use of polyphosfates such as Borron NF in soaking, liming and deliming, could also become helpful * reduce bating time; the more the hides are putrefied (ammonium smell in the presoaking float; hair slip after main soak) the less bating should be done * Use complexing acids in deliming instead of only ammonium salts, such as 0.3% fatty alcohol (Borron SAF) after salt before acid to distribute natural grease uniformly through out the pelt in pickling * to actively reduce vein marks, it is best is to make a strong tanning and a good filling retannage of hides. * use 0.3-0.5% Magnopal TGR in basification to make the grain more tight, flat and to fix more chrome. In the tables are two recipes, which could be used to minimise both growth marks and veins.