Now the skin is ready for the working eycle, which we have summarised in the following phases:
SOAKING: this phase has the purpose of bringing the back to the condition that it was in straight after flaying. It is necessary first of all to give back all the water lost during the preservation treatments and it must be cleaned of such impurities as blood, excrement etc. Another important function of soaking is that of solubilising part of the globular proteins and albumins. This operation has to be carried our with different techniques depending on the type of skin used. The skins which we use do not require particular skill as they are fresh salted skins and the duration is no longer than 12-24 hours in most cases. In any case it has to be taken into consideration that a skin that is well soaked, that is soft and clean, will react much better to subsequent treatments. When the soaking is complete, the skins are drained of excess water and then weighed, thus obtaining the soaked weight, on the basis of which the quantities of products necessary for the following operation, liming can be calculated.
is a treatment through which the skin is of all those substances which
cannot be trasformed into leather, that is the epidermis (with all its
productions) and the subcutaneous layer.
the liming having finished, a washing process is now necessary to ease
fleshing, as otherwise the skin would be slippery and therefore difficult
DELIMING: deloming eliminates alkaline substances which have permeated the skin: sulphurs,sulphydrates and lime. Thus the skin's ph, which was higher than 12 after liming, is brought down to a ph of 7.5 - 8.5, values at which it is possible to carry out the bating. The skins must be stressed in the drum as little as possible and at a low number of rotations (4-6 per minute). Before carrying out this operation the skin needs to be washed with water (300%) in order to clean it and to eliminate the most part of the lime. Then we add 2% ammonium chloride (nh4ci). Therefore with deliming, the skins that have undergone the liming process and which appear swollen to various degrees, "deflate" and the ph is taken to levels of 7.5/8.5. The drum is 1-2 hours and it is the left to rest for approx. 12 hours.
the aim of this phase is to eliminate the protein residues which are not
needed and follicle and epidermal residues; to loosen the skin fibres,
thus completing the liming preparation; furthermore it must make the grain
smoother and cleaner. To do this bates are needed, which at the beginning
of the century were merely dog and pigeon excrement, whereas today enzymes
extracted from the pancreas mixed together with ammonium salts to lower
the ph are used. Small quantities of enzymes are needed to react and they
must be diluted on an inert support. In our case this is how we operate:
we add 200% water, 1% ammonium chloride and we turn the for 20°; after
that we add 1% enzyme oropo r and we turn for 50'. This all must take
place at a temperature of 36-37° and at a ph of 7-8.
after thr skins are unhooked and left to rest for a day, they are staked
with a special machine called staking machine, to make the skin soft and
with a round feel. The skin is then rolled, this machine giving the skin
a finer grain.