How Leather Hides Are Made
Are you interested to know how leather hides
are made? Well, here's a quick guide through the tannery.
Before I start, let me tell you about a lady I met who was absolutely
horrified when she found out that her yellow leather chair was
dyed and spray finished.
 "You're
joking!", she said. "I thought that was the natural colour
of the leather!"
Now really . . . have you ever seen a YELLOW COW? How about a
BLUE one?
It just goes to show how a lack of knowledge can create some
pretty wild and abstract ideas.
To put an end to some of these, let's take a tour through
the tannery . . . the place of many secrets!
A Quick Tour Through The Tannery
1. THE ABATTOIR
Once the hides are removed from the cow, they are cured by soaking
them in a salt solution. This is to stop them from deteriorating
and going rotten. After this process, they are sent to the tannery.
2. LEATHER HIDES CLEANED
The hides are then soaked and cleaned to remove the salt solution.
A lime solution is added to remove hair, dung and excess flesh.
And believe me, this process really stinks!
3. SORTING THE LEATHER
The hides are sorted according to the amount of defects they
may have such as scarring, tick marks, barb wire marks and holes.
Upholstery leather requires larger areas of unblemished hide,
whereas other leather products such as shoes, saddles etc can
utilise the smaller pieces. As a result, this makes upholstery
leather generally more expensive.
4. SPLITTING THE HIDES
The hides to be used for upholstery are then split into two.
The top is split away from the bottom using a machine with a very
long, sharp blade. The top layer is called the 'Top Grain' or
'Top Split', whereas the bottom layer is called the 'Bottom Split'.
Now the 'Top Grain' is the strongest and most supple part of the
hide and this is used for upholstery. The 'Bottom Split' is used
in other products such as shoes, etc.
5. TANNING THE SKINS
The hides are then put into a large rotating drum of chemical
to preserve them . . . permanently. This is called 'Chrome Tanning'.
This also helps to increase the strength, durability and reduce
shrinkage.
6. SORTING AND GRADING THE LEATHER
After tanning, the hides are then graded. This is a process of
sorting out the hides according to their quality which is determined
by the number and size of imperfections such as those mentioned
in the sorting procedure.
7. RE-TANNING & DYING THE HIDES
The leather is put into another large rotating drum of chemicals
which include oils for lubricating and softening, and other chemicals
for adding firmness, tear strength and fastness. Dye is also added
to stain the leather to a colour that is related to the finished
colour.
8. THE LEATHER IS DRIED
As you can imagine, the leather is absolutely saturated at this
point and is then stretched out on large frames and force dried
in a drying room.
9. EMBOSSING THE SURFACE OF THE LEATHER
Leather with excessive scarring is then sanded smooth and embossed
with an artificial grain.
Corrected Grain Leather
If you have seen leather that has an even grain and looks a bit
like vinyl, then the chances are, it has gone through this process.
This type of leather is 'CORRECTED GRAIN' leather and an example
is shown in the picture on the right.
Full Grain Leather
Now 'FULL GRAIN' leather has had nothing done to alter the natural
surface and is softer and contains the natural markings of the
hide. The next picture shows an example.
10. SOFTENING
The leather is then softened in a large rotating drum, very much
like a tumble clothes dryer.
11. PIGMENTING THE LEATHER
The leather is put through an automated finishing machine, which
sprays on the desired colour. Normally several coats are applied.
12. SEALING THE LEATHER
Once the colour is applied, a clear sealer is sprayed on for
added durability. The lustre of this coating can be adjusted to
give a high gloss, satin, or dull finish. The sealer has waxes
and modifiers added to give the leather its feel qualities.
13. LEATHER HIDES ARE WAREHOUSED
The leather is finally graded according to quality, colour and
weight. Each hide is then put through an automated measuring machine,
to measure its area. Upholstery leather measures around 4.5 to
5 sqm.
 How
Are Leather Hides Tested?
Each batch of leather is tested to make sure that the quality
remains up to standard. The following are some of the major tests
performed:
A laboratory device is used to test the ability of the leather
to resist fading.
Upholstery leather should be able to stand up to normal use without
the finish rubbing off. The rub fastness is tested by a machine
where a piece of felt is rubbed back and forth against the leather.
The felt must be able to rub across the leather a certain number
of times without damaging the finish.
A machine flexes a piece of leather thousands of times to simulate
years of wear and tear. The leather is checked for cracking and
splitting.
The adhesion of the finish is tested by gluing a metal plate
to a piece of leather. The force that is needed to remove the
plate is measured.
The tear strength is tested by a machine that holds a piece of
leather and pushes a metal probe into the leather. The amount
of force needed to puncture the leather is measured.
A piece of leather is put into a machine very similar to the
one used to test rub fastness. Instead of using felt, a block
with sandpaper is used.
Well, this is a quick overview of how leather is processed and,
if you ever get a chance to go through a tannery, you will find
it to be a fascinating place.
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