Smelting
When smelting began at Amlwch is not certain.
However the system has been described in a number of eye witness
accounts.
It is thought that the initial smelters were built alongside the
Afon Amlwch in an area now know as Craig y don. The original
building was 112 feet long by 50 feet wide. The river was diverted
to make a small reservoir to be used in the works.
In 1797 Aikin described the smelting works.
The two smelting houses, of which one belongs to each company,
contain 31 reverbatory furnaces, the chimneys of which are 41 feet
high. They are charged every 5 hours with 12 cwt of ore which yields
½ cwt of rough copper, containing 50% of the pure metal. The price
of rough copper is £2-10-0 per cwt. The coals are procured from
Liverpool and Swansea.
The smelting works at the end of the 19 th century.
Lentin in 1800 said only 20 smelters remained in the Amlwch area.
He described the smelting process in great detail and compared it
with the processes used in his native Germany
...The first operation, which is carried out with the ore in the
smelting works consists of further divesting the ores of the
Sulphur, which had not been removed during the first roasting...
...The chimney or flue of such a furnace must be 55 - 60 feet high,
rise vertically and be one square foot internally. This height is in
no way superfluous, rather the intensity of the heat depends on it.
There is no longer any doubt that the heat does not originate in the
fuel but rather comes from the oxygen air that is a component of our
atmosphere. In this air the fuel is so bound through a substance
which the analytical chemist calls oxygen, after Lavoisier, that it
cannot express its propensity to heat. This oxygen can, meanwhile,
be removed at suitable temperatures by several bodies, in
particularly carbon which is copiously contained in all combustible
substances, and what results then, depending on how fast the
separation occurs, is either gentle warmth or the most intense heat.
Because all metallurgical smelting processes and, in particular, the
copper smelting process, demand very high temperatures, one has to
endeavour to construct a smelting furnace which allows for the
decomposition of the largest possible volume of oxygen air in the
shortest possible time.
...I have already said above that calcining furnaces are built
following the same principle as the smelting furnace and that they
only differ themselves in that the hearth is horizontally bricked up
with fire-proof artificial stones. Yet I have to note that instead
of the openings which Schlüter presented in his drawing as the tap
hearth and as the discharge opening, through which the slag is
removed, there are two large openings affixed which can be closed
with iron trapdoors and serve to introduce the ore, and following
that to stir it.
In such a furnace two to three tons of ore 40 - 60 hundredweight are
shovelled through both of the openings just described, evenly spread
about and initially subjected to a roasting heat, which, however,
towards the end of the operation is greatly increased. During this
time the ore is frequently stirred with iron rods which are affixed
to rollers on the front of the furnace in order to control them
better.
The time which is required for sufficient Calcination of such a
quantity of ore cannot be set because it depends on the degree of
roasting which the ore has had; usually, though, 12 hours is
sufficient. Actually it often does not require even that much time
to separate off all the Sulphur present, which can be separated by
this method.
At this point the calcined ore is brought to the foundry and smelted
with the addition of flux in the following way. To 12 hundredweight
of ore, which constitutes a load for this kind of furnace, 42
hundredweight of copper slag and two hundredweight of carbonized
anthracite or coke are added. The anthracite is carried in first,
then the ore and over these comes the roughly broken up slag.
Everything is thrown into the outlet using a shovel; For the
opening, found in Schlüters drawings through which the ore should be
placed into furnace with a funnel, is not found on a copper smelting
furnace, and the outlet is stopped up with a door of clay and
cemented shut. A roasting heat is applied for about one to one and a
half hours so that, if there were still Sulphur present in the ore,
this could completely volatilise. The temperature of the fire is
raised to the highest degree and maintained at this level,
uninterrupted, for two to three and a half hours, which is why the
anthracite is always added in small portions, so that no noticeable
decrease in temperature takes place through adding too great a
quantity. Then the door of the outlet is taken away to check the
state of the smelting, which should be so far along that the mass is
nearly fluid but the slag is still semi-solid.
The smelter then throws a few shovels full of anthracite over the
melting mass, closes the outlet again, increases the heat and keeps
it at the highest temperature until the smelting is complete. This
takes about six hours from the beginning of the operation.
During the smelting the tap hearth which consists of a frame of iron
plates six feet long, three feet wide and 18 feet high, is put in
order. The forms into which the whole molten mass will be poured are
prepared in these using damp sand. The shape of the forms is
arbitrary; however, one usually gives the shape of an inverted
pyramid which has an upper surface eight inches wide. There are as
many of these shapes cut into the sand as space allows, with a space
of four inches between each one, in which a communicating gutter is
cut so that the excess molten material from the first can flow into
the second and that from the second into the third, etc. The form
which is connected directly with the tap is cut out a little wider
and deeper than the others because it mainly takes the metallic
part, while the others, in contrast, are filled only with slag.
When the ore is sufficiently melted, then the furnace is opened,
which is achieved by cleaning away the clay which has sealed the tap
hole or mouth of the furnace with a scraper after which the molten
mass runs into the forms. When all the molten material has run out
of the furnace, the furnace is charged anew by throwing little,
moistened pieces of anthracite into the hearth so that the heat
drops, whereupon one puts in the hard coal and other ingredients.
And so the smelting operation continues, uninterrupted, and one puts
40 hundredweight through the furnace in 24 hours.
When the mass in the tap hearth is suitably cooled down, the pieces
next to the tap hole are removed and the slag is separated out from
the metallic part. This is achieved very easily with a few blows of
the hammer. The slag is thereafter brought to a special place where
one breaks it into bits in order to get out the stone granules which
might still be there, although this does not often occur because the
smelting proceeds very completely, and the mass remained in the
fluid state in the furnace long enough so that the metallic portion
could separate out from the slag. These metallic parts have a
blackish green appearance, are granular and compact like basalt when
broken and sound like it if one hits them with a hammer.
The reguline or metallic portion, which is in the same state as that
which the people in our copper works call Sporstein, is broken into
pieces the size of a fist, and 60 hundredweight of it is brought to
a special furnace, which has the same construction as the smelting
furnace, with the exception that, instead of a tap hearth, a water
container is brought near the furnace and is set up so that fresh
water can flow continuously.
In this furnace the stone is roasted for 12 - 16 hours; the heat is
then gradually increased in intensity so that the mass melts, and in
this state about a hundredweight of anthracite is thrown onto the
melting mass. When everything is quite fluid, the slag which has
been produced on the surface is removed. A lead gutter lined with
clay reaches from the tap hole to the water container. The fluid
stone flows along the gutter into the water where it is granulated
into pieces the size of beans through the constant movement of the
water.
The purpose of this operation is first to fluidise a part of the
Sulphur through the long roasting and then, through the subsequent
granulation, to produce a greater surface area in order to be able
to dislodge the Sulphur more effectively.
After the granules have dried somewhat, they are put into a
calcining furnace and calcined with very active stirring for 26
hours at a temperature as intense as one can use without melting the
mass. Then the granules are melted in a smelting furnace, which does
not have a tap hole and whose hearth is so constructed that the
greatest depth is in front of the outlet.
When everything is sufficiently melted, the slag is removed, and the
molten mass is emptied into iron boxes washed out with clay using
large ladles. The boxes are 16 inches long, 11 inches wide and 11
inches deep, and one places a suitable number of these in a
half-circle in front of the furnace. Two workers, who have pulled
moistened sleeves of rough linen over their arms to keep off the
heat, alternate in taking a shovelful of the material from the
furnace and fill the boxes one after the other, in that each one
pours a ladleful into a box. While the last box is being filled, the
metal in the first has solidified to such an extent that a new layer
can be poured on to it without binding with the first. So the boxes
are filled, one after the other, producing a number of thin cakes
which are approximately 1/4 inch thick and which can be separated
when they are properly cooled.
The purpose of this procedure is to give the mass, which is now in
the state of a very impure black copper and which one can no longer
break into bits, a large surface area so that the pieces of Sulphur
still present can be more easily volatilised.
For this purpose the cakes of black copper are put in another, but
similarly constructed furnace, where they will be roasted for 16
hours with the heat increasing in measured increments, so that the
metal melts very slowly. After everything is fluid, one allows the
metal to simmer for a few hours so that the calcined parts can
scorify, and one removes the slag through the outlet. Then one lets
the fire die down a bit and pours the fluid black copper into iron
boxes as before.
The metal is now in a state where it can be purified. This, however,
does not take place in the same way as in our own copper works but
rather in a way which distinguishes it, in that the copper at these
works is made completely pure immediately so that it can be worked
by coppersmiths without further refining.
To achieve this one places the cakes in the refining furnace, which
is just like the previous furnace, and roasts it for 16 hours,
gradually increasing the temperature so that the copper melts
slowly. When this has happened, 25 to 30 pounds of lead is put onto
the three tons of copper which one will refine all at the same time.
Then one maintains a strong heat for several hours so that a proper
slag can form and the impurities still found in the copper can
dissolve out. The slag is removed from time to time so that the
calcination of the metal pieces being scorified can proceed even
better with the introduction of fresh air.
When the scorification is coming to an end, enough coal dust is
thrown on to sufficiently coat the surface of the metal. Then the
refiner shoves a tree in the furnace and presses it into the metal
as strongly as he can. Because one uses elms or young oaks from four
to six inches in diameter which have been freshly cut or left to lie
in water to keep them damp, a violent bubbling occurs in the copper
when one pushes the tree into it. This is allowed to continue for
several minutes. Then one throws coal dust over the copper again and
the bubbling recurs. This process continues until the copper has
reached the requisite degree of purity. One ascertains this by
removing a little copper with a small test spoon. As soon as the
copper solidifies, it is quenched in water and breaks into bits. If
the colour is a bright brick red, and the break shows that it is
fine-fibred and as glassy as satin, then it is of the required
purity. If, on the other hand, it is blistered inside and dark red,
then one has to carry out the previous procedure, which one calls
phlogistics for a longer period of time. One must even add some
lead, if the metal is still not ready, whereby, however, the
phlogistics must always be repeated.
When the copper has reached the desired purity, it is either poured
out as cakes in the previously described manner, granulated or
poured out in small bars, which are formed like bars of sealing wax
and are usually called Japanese copper in Germany but should
actually be called lacquered copper because the English word
japanned copper signifies this. Also it is generally known in
England that all the copper produced by this firm is produced in the
country and is used in business with the East Indies.
The cakes, most of which are treated in the rolling mills of the
company, are usually one and an half inches thick. In order to
maintain this thickness, it is necessary that both of the workers
who do the pouring shovel as quickly and at as regular intervals as
possible so that when the first one has poured out his ladleful, the
other one can follow on immediately so that the metal does not
solidify before the next ladleful arrives.
The boxes are washed out with clay beforehand and the bottom cakes
are only poured thinly because they have to be melted again. When
the pouring is finished, the boxes are cooled in a tank with water.
Then the cakes are taken out, trimmed at the edges, stamped and
numbered and sent off from the works.
Granulation occurs in the following way. A cylindrical container of
copper which can be brought up again afterwards with the help of a
crane winch is let down into a round 12 foot deep tank, through
which water continuously flows, A copperplate dome is place over the
tank, with an opening on one side for the ladle carrying the metal.
This hole must, for this occasion, be much smaller than the hole
used in pouring of the plates because the metal can only be poured
into the water in small portions, on account of the violent
explosion, which would occur if too much metal hits the water at
once, and because too much copper ladled out at once would also
solidify in the ladle. For this reason this process is carried out
by only one worker. He scoops up some copper, puts the spoon through
the opening of the dome over the tank and gradually shakes the
copper into the water where it sinks to the bottom producing
crackling sounds and frequently, blue flames. The copper falls two
to three feet through a column of air before it reaches the water
and by doing this takes on a form which has a distant resemblance to
the texture of a feather. One therefore calls these granules
feather-shot to distinguish them from the rounder granules which one
gets when the copper is poured directly into the water. Because the
granulation takes a lot of time, one has to ensure that the metal in
the furnace does not get too cold; to protect it against calcining,
the surface is dusted with coal dust.
Granulation was used everywhere in England in the preparation of
brass, for which it is also undoubtedly more suitable than refined
copper because the granules consists of very thin plates which can
mix with the calamine better and offer a larger surface area for the
developing zinc vapour to penetrate. However, more of this when I
discuss brass production.
The so-called lacquered copper is poured in the form of ingots.
Several such forms are fastened to an iron wheel which is positioned
over a tank filled with water, which is likewise positioned very
close to the front of the furnace. When the metal reaches the
necessary refined state, a young lad, using a paint brush, paints
the form with oil, and the pouring master, using a spoon which holds
just about what the form will hold, pours the metal in the forms.
In the meantime another worker holds ready a container with water
which he pours on the copper in the form; As soon as the copper
solidifies, he turns the wheel so that the bar cools itself
completely in the water in the tank.
The copper is poured into the form next to the first form following
the same procedure; however, before one paints the form with oil it
is first carefully dried out with a cloth. Otherwise the water
mixing with the molten copper could cause a dangerous explosion for
one of the workers. One uses the forms in rotation so that there is
enough time for them to cool again before introducing molten copper;
otherwise the copper would stick to them.
This is the simple process which produces a quality of copper which
one values so much abroad, which, however, the English smelters who
produce it regard as less pure than cake copper. The oil with which
the forms are painted before each casting serves to hinder the
effect of oxygen from the air as well as the cooling water and keeps
the outer surface completely metallic. The outer surface also
becomes shiny through the sudden pulling together of the particles
in the same way that any metal takes on a higher shine when its
surface particles are brought closer together through pressure,
under the coin press, for example.
The working up of the precipitated copper is less difficult than the
procedure for the ore. At the first smelting one places eight
hundredweight of precipitate with four hundredweight of slag and
half a hundredweight of anthracite in the furnace, takes away the
slag when everything is well melted and pours the metallic part,
which is very impure black copper, in iron boxes to make cakes.
These undergo a 24 hour roasting and are then slowly melted and
poured out. The same operation is repeated again, after which the
metal is sent for refining.
These then are the English smelting and refining processes, which I
cannot leave without first explaining a few operations which are not
common for us and without making a brief comparison between these
and the normal smelting methods used in Germany....