The major constituent of pewter is tin which is produced from tin
ore, the major source of supply being the Far East and South
America. Tin is completely non-toxic, melts at a relatively low
temperature (232° C), has very good fluidity when molten, has good
formability, and readily forms alloys with other metals. It is a
relatively soft metal and it is for this reason that it is alloyed
with other constituents before being used in the form of
pewter.
ALLOYING
The alloys are made up
in large iron-melting pots and after melting and thorough mixing,
the alloy is cast into ingots for producing cast pewterware or slabs
for subsequent rolling into sheets.
In the alloying of pewter it is important that the mix is
accurately controlled both on quantities and temperature for
repeatability. Once manufacture procedures have been established in
a pewter workshop, it is important that the supply of raw materials
is consistent from batch to batch, whether it be casting ingots or
sheet materials.
ROLLING
The slabs of pewter in
their 'cast form' will have a rough surface and the upper surface
will have considerable shrinkage marks and depressions. The upper
and lower surfaces are therefore machined off. The slabs are then
passed through banks of rolling mills which progressively reduce the
thickness. It is important that the rolls of these mills are
polished to a high finish and every care must be taken to keep the
sheet clean to avoid dirt or other foreign substances into the
surface. During the reduction process, the pewter softens quite
considerably from its original 'cast' hardness. This is mainly due
to a reduction in crystal size and distribution caused by the
rolling and reducing action. The rolling and reduction continues
until the desired sheet thickness is reached.
SPINNING
Spinning is a
metal-forming technique, done on a suitable spinning lathe, by which
flat sheet can be easily formed into hollow vessels. Using formers
or burnishers, the spinner works the pewter discs on to former
chucks which come in many and various shapes and sizes.
PEWTERSMITHING
Pewtersmiths are
experienced in soldering which makes it one of the most important
techniques in the pewter workshop, as it is the standard method of
joining individual components to form an assembly. When carried out
with skill and the correct materials, the joints are extremely
difficult to detect. Using various solder alloys for the many varied
items made nowadays, the pewtersmith has to use his skill in
bringing the components to a soldering lamp, or in certain
circumstances the lamp to the component.
CASTING
Casting is the oldest
method of producing pewterware and in some countries it is still the
dominant method. Gravity casting into permanent metal moulds is the
traditional technique of producing cast pewterware. The technique
has been in existence for hundreds of years, and even today, the
bulk of cast pewter is produced by this means.
Slush casting is a method of making hollow castings without the
complexity of using cores, particularly where the profile or surface
finish of the inside is relatively unimportant. This makes it an
ideal method for reducing the weight of a handle or other attachment
to a main article without upsetting the balance or feel.
Rubber mould casting by the centrifugal method is, today, a very
common method of producing small items quickly, accurately and to a
high standard of finish and complexity. Impressions are formed in
two thick circular sheets of rubber, which are then clamped
together. The top sheet has a central hole which connects with
runways in the rubber which lead to the impressions. Molten pewter
is poured into the central hole of the top sheet, whilst the mould
is rotated at high speed. The pewter is forced along the runways
into the cavities by the centrifugal force. When the metal has
cooled, the two halves are parted and a radial display of cast parts
is seen.
FINISHING
Finishing is the last
process in the production of a piece of pewterware, but is by no
means a technique tacked on to the end of the other processes. It is
the finish that determines the final appearance and characteristics
of a piece of work. Firstly, stitched mops dressed with abrasive
compounds are used to cut away the surface, to remove irregularities
and imperfections. This is then followed by the final polishing on
swansdown mops, using rouge based compound. This gives an extremely
fine, sometimes mirror, finish and brings out the colour of the
metal.
It can be seen that there are many different skills in the making
of pewterware, too many to fit into this short introduction. The
skills mentioned have been handed down over the centuries and the
craftsmen of today are still proud of their heritage. We owe them
all a debt of gratitude for their continued efforts to turn out
superior articles of beauty.
