Process

Skin is hardly useable in its natural state because it is subject to rotting and temperature variations. tanning therefore has the function of eliminating these problems by using suitable substances of vegetable, animal and synthetic origin. skin is made up of 1% epidermis, 85% derma and 14% the subcutaneous layer or "flesh". the part which tanning involves is exclusively the derma that hence becomes leather. this is constituted by strips of fibre composed of finer fibrils, which interweave and form a net of tissue. in the tanning activity it is important to distinguish between the upper part of the derma, which touches the epidermis, which constitutes the grain, characteristic of every animal species, and the underlying part known as the flesh split.

After the skin is naturally flayed and salted for preservation, it is suitably cut depending on the type of part of skin that we wish to produce. our company, using all the skin, will carry out the so-called "offal rounding", that is from the skin we obtain the "shoulders", and a pair of sides, as is illustrated in the diagram alongside ). we carry out the rounding by hand as every skin is different.

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.

LIMING: 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.
At the same time changes are made to the fibrous structure of the derma with a collagen regulated hydrolysis. The liming process therefore obtains:

DEPILATION

PARTIAL SAPONIFICATION OF FATS


A MORE OR LESS PRONUNCED SWELLING OF THE DERMA:limed skins appear slippery, swollen and very sensitive to mechanical and chemical processes and to changes in temperature. Liming is considered fundamental in working skins because errors in carrying it out are difficult to put right with the subsequent operations.

FLESHING-TRIMMING-SPLITTING: the liming having finished, a washing process is now necessary to ease fleshing, as otherwise the skin would be slippery and therefore difficult to work.
By doing this the ph again becomes neutral. The fleshing is carried out using a machine with a carrying cylinder covered in hard plastic, upon which the skin is placed; this cylinder is operated by a pedal which puts it into motion in order to bring it nearer another cylinder, this with propeller blades, which rapid rotation takes off the flesh.
Now the grain, defects and various small surface cuts can be clearly seen. After that we go on to splitting which is carried out with the splitting machine. It works by passing the skin between two cylinders where there is a spinning blade which divides the grain from the flesh split.
Following these operations the pelt weight of the skin is obtained, on the basis of which the percentages of products needed for the operations up to and including tanning can be calculated.

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.

BATING: 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.

ACIDIFICATION: at this point the skin, which is still in the drum, is acidified, that is the ph is taken from 7-8 to 4. Only now is the skin ready for tanning.


TANNING:
tanning is essentially the impregnation of the skin substances that fix onto the skin irreversibly and prevent rotting without (photo?) Altering the softness, flexibility and structure. The tanning method that we appy is strictly vegetable and uses vegetable tannins such as mimosa, chestnut and quebracho.

FATTENING: after tanning the skins are taken out of the drum and spread out on a level surface. After this they are put on a press (see photo) which removes the excess water inside the skin. After approx. 4 hours of pressing the skins are put back in a special drum for tallow fattening where the skins are fattened.






SETTING OUT:
the skin is then out of the drum and after a day of rest is set out, that is smoothed out on a machine (see photo). This machine puts a strong pressure on the skin with a cylinder with specially set out blades, which flattens the skin as much as possible. Thus the grain of the skin is well smoothed and the fibres themselves are all placed in the same direction and the resulting product has superior physical characteristics

DRYING: the treated skins are completely dried in 4/5 days at temperatures which vary from 20 to 30 degrees. Drying must be performed with care and our skins are hung to air with special hooks in order to dry the skin in the most natural way possible.

STAKING: 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.

Now, after being worked for about a month, our vegetable-tanned kip type skin is ready to be worked by our esteemed customers.