[The earliest times]
 Seaweed
burning
Dried seaweed burnt to produce edible salt-fiavoured
ashes
Sea-weed ashes soaked in sea-water, yielding
brine-concentrate liquid
Dried sea-weed washed in sea-water to produce
brine-concentrate
Use
of salt-beach production sites (sea-weed displaced
by salt-bearing sand)
The
use of sea-weed as a source abandoned in favour
of beach sand as a more efficient medium of salt
extraction (eighth century)
[Middle ages]
Construction
of salt-terraces with channels
Beach
sites gradually enhanced by man-made improvements
(ninth century).
Channelled
terrace prototypes.
Tidal changes utilised to flood salt-gathering site.
Method applicable in areas with marked difference
between high and low tide.
Natural
beaches
Unbanked tide flats or lagoons used in their natural
state, without man-made sea-walls.
Sea-walls,
and other improvements added; classic channelled
salt-terrace field form develops.
Banked-terrace
prototypes
Sea water carried to terrace by workers at site.
Method applicable in areas with minimal tidal difference
(the Japan Sea coastline) or in location's with
rough seas (the Pacific coast)
Natural
beach surfaces
Most common form; beach surfaces in natural state
used during the summer season.
Artificial
sand-terraces
Frequently found on the Noto
Peninsula and in southern Kyushu.
[Eariy modern era to Modern
era the present]
Channelled
salt-terrace systems.
From
the Edo period on, large-scale constuction carried
out in Inland Sea area.
Terrace
systems form basis of a full-scale industry.
Single-stage
salt boiling
Impracticable
except in north Pacific districts.
[Modern era the present]
Sloping
salt-terrace systems
Inclined
sand-terrace surface and evaporation racks are combined
to achieve more efficient use of solar and wind
evaporation. Employed at traditional channelled-terrace
sites from 1952 to 1959.
Ion-exchange
system
Electrical
energy is utilised to produce brine-concentrate
solution. This method was adopted in 1972; it replaced
the sloping-terrace method at commercial sites.
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