[The earliest times]
 Earthenware
salt-boiling vessels
 Sea-weed
used in the manufacture of brine-concentrate, which
is boiled down in clay pots.
Salt-pans
and kettles
With
larger kettles, substantial amounts could be more
efficiently processed.
Clay
salt-pans (used in many areas).
Ashes of sea shells were mixed with wood-ash
and clay to produce mortar for making large vessels.
Imported
iron kettles (eighth century).
A small number of iron salt cauldrons arrived from
China during the Nara period.
They were rarities of great value, not generally
used in ordinary salt production. A unique fragment
of an ancient cauldron is preserved at the Kanaya
Shrine in Chiba Prefecture.
[Middle ages]
Reed
salt-pans (South-western Kyushu).
The "reeds" were genarally bamboo fibres plastered
with clay or mortar. Also known as "bamboo kettles".
Stone-lined
kettles
These were lined with stones set in mortar.
Domestic
iron kettles
In
post-Nara times, Japanese kettles appeared.
Early
kettles at Shiogama Shrine.
Of the four ancient specimens at the Shiogama ("Salt
Kettle") Shrine on the coast of Miyagi Prefecture,
the oldest dates from the twelfth cerltury, while
the others are believed to have been cast during
the fifteenth century.
Other
traditional cast-iron kettles (Noto Peninsula, Ise
district, and elsewhere).
[Eariy modern era to Modern
era the present]
Giant
stone-lined kettles
Used
in the Ten Salt Provinces.
(Average size: 2.7m by 3.6m, with depth ranging
from 12 to 15cm)
Wrought-iron
kettles .
These were made of iron ships welded together.
They were used in the direct boiling method on the
north Pacific coast.
Western
style salt-kettles
After
1868, these replaced stone-lined ketlles.
[Modern era the present]
Improved
cauldrons (1928).
Preliminary
steam-heating system
From
1935 on, steam produced during crystallization was
used to warm brine-concentrate awaiting final boiling.
Vacuum-evaporation
process
In
1927 the first experimental plant was opened. During
the following decades the new method was adopted
throughout all major salt producing districts, where
it remains in use today.
In
1971, large-scale installations of vacuum-evaporation
eqipment were carried out.
Vapour
compression system
Large-scale
direct production of salt from sea-water was begun
in 1952. This method remained in use until 1971.
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