(See “Waste Utilization”)
Since the Crown Seal stopper, for beer bottles particularly, has come
into vogue, there has been a great demand for cork disks which form the
medium for air tightness and this has given the cork-worker an
opportunity to utilize a grade of corkwood that usually had but little
commercial value, that is, a thin bark.
It may be well to state here for the uninitiated that the Crown Seal is
made up of a tin cap, corrugated on the lapped edge, for gripping the
top of the bottle, a corkwood disk and a water-proof paper between the
disk and cap, a very ingenious device.
As you have already read in a previous chapter that corks are cut
vertical parallel, or, to state more clearly, the axis of the stopper
must be parallel with the axis of the tree that furnished the bark; and
the desired direction is easily recognizable by the colored striae due
to the annual layers of suberous substance that are observed in the
direction of its axis, this rule being followed because cork is found to
be more impervious to liquids if cut in this manner. It will be readily
seen that if disks are cut horizontally parallel, that is, the annual
layers running at right angles to the axis of the disk, this grade of
cork can be utilized to great advantage. The mode of cutting is by a
horizontal revolving blade, which slices the cork to the desired
thickness, usually a quarter of an inch, and then it follows the usual
course of punching, etc. From these operations a great deal of waste
accumulates, and this would be a great loss if methods were not devised
for its utilization. Many firms work up this waste on the premises, but
most of it is shipped out and its conversion forms a separate part of
the corkwood industry, which will be described later. We might say now
that the cork is made, for it has been cut and shaped into the desired
commercial size; and all that remains is to sort them and ship them
away. But if commerce desires sizes and quality, it has also exacted
many other requirements of a cork before it is acceptable and we will
now take up the further manipulation of cork before it leaves the
factory. Naturally, this corkwood, coming such a distance and being
handled by so many in the general processes just described, gets more or
less dirty, and aside from that perhaps in the growing the tissue has
not remained as white as is desired, so before the cork can leave the
factory it has to be washed or cleaned. And in this washing I will not
say that there is not an attempt to improve the looks of the corks in
order to get a better price. Now this washing or bleaching is carried on
in the simplest manner and is just soaking the corks in water and a
chemical and then placing them in a centrifugal spinner, which is
nothing more than a perforated receptacle made to revolve within an iron
jacket, which is connected to a drain, naturally forcing the material
against the periphery and thereby causing the excess water and acid to
pass out through the perforations, this system becoming quite common in
cork factories to-day, greatly facilitating the drying, which is done
mostly by the atmosphere. This is all there is to the mechanical part,
but curiosity prompts us to inquire what chemicals are used to clean the
corks, so I have ascertained the principal ones, but of course every
manufacturer will have his own way of doing this part of the work,
although the principle remains the same. An old way was to wash them in
water containing chloride of tin or oxalic acid and then subjecting them
to the fumes of burning sulphur, but the sulphur bleach has been
discontinued. Bioxalate of potash has also been used in solution, as
also chloride of lime, ammonia and sulphuric acid. Another way is to
wash in a 10 per cent solution of hydrochloric acid and then immerse in
a solution of sodium hyposulphate and hydrochloric acid, finally washing
with a solution of soda and water. All of these produce the desired
effect when mere cleaning and bleaching is all that is required: but in
the poorer grade of cork, mostly a thick cork that has been jaspered or
contains micro-organisms, a system of treatment with formol or methylal,
ethyl alcohol or spirit wine and formaldehyde and impregnating with
casein has been used. These bleaches are applied to regular stoppers and
disks alike, but in addition to this the disks are given a bath of hot
paraffin, or glycerine and paraffin, which improves their resistance and
retards discoloration. This generally being done in a steam-jacketed
kettle, or tumbling barrel, and then placed in a centrifugal to remove
the excess of water and paraffin.
In some factories, and when the customer requests it, the name is
branded upon the stopper by irons heated by gas, gasolene or in a coal
fire, automatic gas heated machines being most general.
In the foregoing it has been shown how the stopper and disk are made,
and although there are many different manufacturers of corkwood
stoppers, it will be found that the _modus operandi_ just described is
followed generally, with perhaps a variation in the details. The waste
material, “recortes” as stated is collected and used in various ways,
but either in conjunction with other materials or alone in a granulated
or powdered state.
The following chapter will enumerate the three principal uses of waste
corkwood, and as these cover the fundamentals of the other uses it will
not be necessary to describe them, e.g., linoleum, made by mixing
cork-flour and linseed oil.