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The way in which hollowware such as
saucepans, kettles and dishes have been made is a good guide to quality, age
and durability. Methods differ between craftsman coppersmith and quantity
production and have changed through the years. Both can achieve fitness for
purpose and both methods have always had to be made at a price to suit the
market. The production techniques involved can include cutting, raising,
seaming, deep drawing, spinning, brazing, welding and riveting. For cooking
utensils, the insides are usually tinned after manufacture. Some recent
production is of course intended only as interior decor rather than being
for serious use.
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Hollowware has to be produced as a
three-dimensional vessel from flat sheet since neither casting nor hot
forging are usually economic options. Methods have developed significantly
through the centuries and these are generally obvious in the finished
product. Initially, the basic need is to form the sidewalls and join them
to a base. Spouts, handles and lids are fitted as needed. Traditional
techniques involve cutting out copper sheet to form the sidewall, forming it
to cylindrical shape and making a joint.
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A brazed butt joint is not strong enough
so an overlap must be used to give a bigger contact area for the join. A
simple overlap is still not strong enough to take a battering in service, so
the coppersmith’s technique is to make what appears to be a
‘cramped’, ‘dovetailed’ or ‘castellated’ joint. This involves forming a
feathering by hammering the edges of the sheet to about half their original
thickness and then cutting slits at right angles to the edge. These are
bent out alternately and mated with the edge to be joined. The flaps are
then hammered close to give a good friction fit that can be sealed by
brazing or silver-soldering. Note that the description ‘Dovetailing’ gives
a joint of different type to that found with wood. The ‘dovetails’ are not
keyed together right through the joint as for wood but overlapped and
cramped as described. Coppersmiths much prefer to describe the joint as
‘cramped’.
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Final finishing is by
planishing the joint surface flat, so that it is the same thickness as the
parent metal sheet. Normally, any handles or spouts are positioned to hide
much of the sidewall joint. |
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As metalworking production
techniques improved during the later 19th century it became
possible to make tools to cut a regular castellated edge to copper sheets.
This made joint making a much quicker and cheaper process. The serrations
are usually closer spaced than hand cut joints. |
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To fit the base to the
sidewalls with good quality smooth joints it is necessary to either bend up
the circular base to fit the sidewall or bend the sidewall under to allow
the base to be let in. The second technique keeps the brazed joint out of
sight under the vessel. These methods were used commercially in Europe and
America until around 1900. The technique can still be used and is still
seen on some modern imported products, frequently not of such good quality. |
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Improved machines have made
it possible to make deeper and deeper vessels out of one piece of flat sheet
by deep drawing or spinning. |
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Another way of making joints is by using
lockseams. This can be done by hand or machine and involves folding over a
narrow strip of metal from each of the pieces to be joined, interlocking
them, and soldering the joint to make it permanent and watertight. |
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A water can
made by Perry & Sons in the early 1900s that shows good quality lock seams.
The handle has laps either side for strength and the ribs add decoration and
rigidity. |
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Using a filler of high-zinc brass
it is easy to make brazed joints in copper items. Traditionally, this
was the filler used to finish cramped joints before hard solder became
available. It takes skill to make the joint neatly.
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An example
of poor quality recently made jointing and brazing that has been carried out
in making this lidded jug with far more enthusiasm than skill. |
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Hard solder is a
copper-silver alloy that melts at a lower temperature than braze metal.
It is used sparingly on joints made with fine clearances and leaves very
tidy joints. |
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Traditionally, handles were fixed to the
body of a vessel by riveting using copper rivets to give a good strong
joint. Before rivets were available commercially they were made by the
coppersmith from offcuts of copper folded and hammered to a round shape to
fit the holes. Careful hammering ensured that a very neat joint was
produced. Commercial rivets still need careful hammering to give a good
round head with no splits.
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A splendid
riveted repair to a damaged Victorian kettle that stands the test of time. A
unique item for collectors! |
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A really
ugly riveting job on a modern hand-made jug not made in Britain. The handle itself is also
split at the joint. |
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Where joints may still be needed in the
production of deep modern copper cookware, overlap and brazing has been
replaced as a jointing technique by mechanised arc welded (MIG -
metal-inert-gas) butt joints. Even after weld dressing, feint traces of the
joints may be evident but do not affect the fitness for purpose of the
products.
Arc Welding can now also be used for
making butt joints in thinner metal for holloware such as jugs. Initially
the development work was as an automated process to speed up the manufacture
of domestic hot water cylinders. Having succeeded for light duty pressure
vessels, the technique is now also used to help make holloware. Weld
dressing is needed to give two good smooth sides to the joint.
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is a
craft that developed when it became possible to keep a lathe revolving in
one direction rather than use a bow string to drive it in alternate
directions. A flat disc of metal is clamped against a shaped former held in
the chuck. While this rotates, a wooden tool is held against it and
pressure is applied to gradually form the disc to the shape needed. Bowls
are easily made and vessels with parallel sides are possible within limits.
Spinning marks are left by the tool, these being circumferential.
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Deep drawing
This method is now used to produce many
straight sided vessels and gives no need to form and join a separate base. This process also starts with circles that are cut
from sheet. They are held between two pressure rings while a shaped punch
forces the metal through the centre of a die in one of them. As the drawing
takes place, the sides of the vessel are formed by being drawn between the
punch and die. Some items may be made in one operation. Taller items may
need a second or third draw and possibly subsequent forming to make the
designed shape. Longitudinal drawing marks may well be evident, though with
good lubrication and unworn dies they should be minimal and easily polished
out. Frequently traces can be still be seen. The original rolling marks
may still be seen on the un-deformed base of the vessel.
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