[17] The corkwood or cork of commerce is the external part or “periderm”
of the cork-oak; and when it has attained a diameter of approximately
12.7 centimeters or the tree measures forty centimeters in circumference
according to the Spanish governmental regulations, which the tree does
usually by the time it is twenty years old, the bark may be removed. The
stripping generally takes place during July and August, and it is a
process which demands skill and care, if injury to the bark is to be
avoided. In Algeria the French strippers sometimes use crescent-shaped
saws, but under the usual Spanish method a hatchet, with a long handle,
is the only implement employed. The bark is cut clear through, around
the base of the tree, and a similar incision is made around the trunk,
just below the spring of the main branches; the two incisions are then
connected by one or two longitudinal cuts, following, so far as
possible, the deepest of the natural cracks in the bark. Inserting the
wedge-shaped handle, the tree’s covering is then pried off. The larger
branches are stripped in the same manner, yielding, generally, a finer
grade of cork than that of the trunk. The thickness of the bark ranges
from 1.27 centimeters to 6.85 centimeters, while the yield also varies
greatly from twenty to 75 kilograms[18] per tree, depending upon its
size and age. After the first stripping the tree is left in the
juvenescent state to regenerate, and great care must be taken in the
stripping not to injure the inner skin or epidermis at any stage of the
process, for the life of the tree depends upon its proper preservation,
for if injured at any point, growth there ceases and the spot remains
forever afterward scarred and uncovered. It is also necessary to avoid
stripping during the prevalence of a sirocco, which would dry the inner
skin too rapidly and therefore exclude all further formation of cork.
[17] Armstrong Cork Co.’s pamphlet.
[18] Kilogram = 2.205 pounds.
The Capgrand-Mothe system, which, as known, consists of dressing the
trunk with the same cork just removed, and leaving it so dressed for a
couple of months, has not met with approval, as being impracticable on a
large scale. After the stripping, the phellogen, the seat of the growing
processes, undertakes at once the formation of a new covering of finer
texture, and each year this, the real skin, with its life-giving sap,
forms two layers of cells, one within, increasing the diameter of the
trunk, the other without, adding thickness to the sheathing of bark.
After eight or ten years this sheathing is removed, and while more
valuable than the first stripping, it is not as fine in quality as that
of the third and subsequent strippings, which follow at regular
intervals of about nine years. At the age of about forty years the oak
begins to yield its best bark, continuing productive as a rule for
almost a century.[19] The cork of the first barking is called
Corcho-Bornio, Borniza or virgin, and is so coarse, rough, and dense in
texture that it is of little commercial value. The second barking is
called “pelas,” or secondary cork, and this and subsequent barkings
constitute the cork of commerce. As the bark is removed it is gathered
up in piles (rusque) and left for a few days to dry. Having been
weighed, it is next carried either in wagons or on the backs of burros
to the boiling station, where it is stacked and allowed to season for a
few weeks. It is then ready for the boiling process. The outside of the
bark in its natural state is, as may well be imagined, rough and woody,
owing to exposure to the weather. After boiling this useless outer
coating is readily scraped off, thereby reducing the weight of the
material almost twenty per cent. The boiling process also serves to
remove the tannic acid, increases the volume and elasticity of the bark,
renders it soft and pliable and flattens it out for convenient packing.
After being roughly sorted as to quality and thickness, the bark is then
ready for its first long journey, and as the forests are generally
located in hilly or even mountainous country, the faithful burro must
again be called into service. Truly the Spaniards’ best friend, though
the worst treated of all, these patient little animals present a most
grotesque appearance when loaded from head to hind quarters with a huge
mass of the light bark. Down from the hills they go in trains of thirty,
forty or even a hundred, threading the rocky bridle paths in single file
and wending their way through the narrow streets of quaint villages
where traces of Moorish occupancy may still be seen, to the nearest
railway station. The corkwood is there freighted to the various sea-port
warehouses in Spain and Portugal, Seville, Spain being perhaps the
largest depository and user of raw material.[20] This historic city,
situated on the banks of the Guadalquivir, presents a very animated
sight in the summer months, and plays a very important part in the cork
industry, for besides the numerous warehouses for storing and shipping
there are factories for the manipulation of cork and its conversion into
the many useful forms in which it has proven of value. Before shipping,
the bales are opened, the edges of the bark trimmed and the bark then
sorted into the various grades of quality and thickness again. The
importance of this last mentioned operation cannot be overemphasized, as
the whole problem of the successful and economical manufacture of corks
center about it. After sorting it is ready to be rebaled for shipment,
this generally being done by placing the large, flat pieces called
planks or tables, at the bottom of the bales, and above them the small
pieces which are covered in turn with larger sections; then the whole
mass being subjected to pressure to render it compact, afterward being
bound up securely with steel hoops or wires. Each bale carefully marked
indicating the grade or quality, loaded directly into ocean-going
steamers and shipped to the ports of the world.
[19] Mr. Lamey, the author of a study upon cork in Algeria, published
some interesting tables in this work regarding the annual
increase and the mean thickness of cork. According to him
cork-bark should not be removed before it has attained a
thickness of 2.032 cm., and the formation of new cork has been
well explained by Mr. Mathieu in his “Forestry Flora.”
[20] Armstrong Cork Co.’s pamphlet.
From this meager description we at least can learn what “corkwood” is,
the limited sphere of its growth, the constant care necessary to insure
a successful harvest or gathering, the peculiarities of the tree, its
longevity and the general mode of preparing the bark for shipment; the
narration in no wise doing justice to this most interesting material, in
its natural state, for its growing is a fascinating tale in itself; but
for the purpose of this writing the foregoing has been deemed sufficient
to convey an understanding of it.
As we have now seen how this wonderful material grows, its haunts and
dwellings, we will look at it more closely and see what it really is,
how this particular formation comes about and its peculiarities.