Millstones,
An Introduction
Notes by Charles Howell
The grinding of grain by primitive hand stones can be traced back even
further
than recorded civilization, although the methods used in prehistoric
milling are
a matter of some conjecture and speculation. It is certain, however,
that stones
used for grinding grain have progressed through the centuries, from the
small
stones held in the hand which were used hammer-like fashion to pulverize
grain
against larger stones or a rock face, to the highly efficient power driven
millstones that are still used to this day.
Geologists and archaeologists have come across primitive types of pounding
stones of a similar shape in various parts of the world. It is interesting
to
note that the methods used to reduce grain or berries to a more edible
form did
not very much by the people in the early civilizations of the Old World,
the
original peoples of the New World, or by the aborigines of modern uncivilized
countries. A similar kind of hammer stone appears to have been in universal
use
perhaps between 25 and 50 thousand years ago.
The improvements in the simple pounding methods came with the introduction
of
the mortar and pestle which gave more of a grinding action. The grain
was placed
in a bowel-like piece of rock, the mortar, and ground by the pestle,
a
club-shaped implement. This was held in the hand and worked up and down
striking
the grain. The same principle was also used with mortars fashioned from
a
section of a hardwood tree trunk, the grain being pounded with hardwood
pestles.
There were, of course, many variations in the kind of wood used and in
the size
of the mortars and pestles. The design largely depended on local timber
availability and the needs of the people using those grinding implements.
From the primitive hand stones, mortars and pestles, was developed the
saddle
stone or saddle quern. This device had a saddle shaped stone base, a
true
grinding action was produced by working a rubbing stone, shaped almost
like a
rolling pin, back and forth across the abrasive surface of this stone
base, on
which the grain was scattered. Later improvements to the saddle stones
were,
having the milling surfaces of a flat base stone and enlarged flat rubbing
stone
grooved so that the grooves crossed each other to improve the shearing
action.
This grooving of these early grinding stones, must have been one of the
first
steps towards a definite pattern of millstone dressing. To assist in
the
operation of the larger rubbing upper stones, handles were fitted at
either side
of the rubbing stone, so that more force could be used in a push and
pull
motion. This type was called a push mill. In later larger versions levers
were
fitted so that the whole of the force of the operator's body could be
utilized.
This improved type of mill was sometimes termed a lever mill.
About two hundred years B. C. rotary motion came into use, this was
a great
improvement and was first developed by the Romans. One of the early rotary
devices was the hourglass mill, or conical quern, in which the upper
stone was
suspended over the conical shaped lower stone. The top portion of the
upper
stone was hopper shaped and used to feed the grain through a perforated
iron
plate fitted in the center of the two sections. This iron plate, called
the
rynd, had a central socket eye which was pivoted on top of a spindle
fixed into
the lower stone, so that the upper stone did not rest directly on the
lower one.
The upper stone was turned by means of bars projecting from its side,
the
operator or operators, walking round the mill. The grain from the revolving
hopper gradually fed through the space between it and the lower, producing
coarser meal; while a thin shim, by bringing the stones closer together,
would
produce finer meal. This method of adjustment, although effectual, was
most
troublesome, as it involved the lifting off of the top stone every time
a change
in the texture of the meal was desired. The later bridge-tree method
is much
easier and more effective. To turn the upper stone, a wooden handle is
inserted
in the top surface of the stone, so that when grinding, the upper stone
revolves
and the lower stone is stationary. The grain is fed in through the eye,
radiated
from the center of the stones and is ground into meal by the action of
the upper
stone passing over the lower one, the meal emerges all round the periphery
of
the stones.
Animal power was also utilized to power the larger versions of the quern.
Even
today, primitive methods of grain grinding by camel, donkey or oxen power
are
found in India, the Middle East and many other countries.
The quern proved to be the only one out of all the ancient hand stones
used, to
survive amongst the majority of the civilized nations. One exception
being
Mexico, which in her present civilization still retains the Metata, which
is
rather an elaborate kind of saddle stone. In remote areas of Mexico,
the
traveler may still witness the grinding of corn by the women of the household,
using these ancient grain stones. Possibly every country in the Old World
has
used, or still uses, the Roman quern. In North and South America and
in Southern
Africa the quern does not appear to have been used. When the Western
Hemisphere
was discovered, the grinding of grain passed directly from the pestle
and mortar
method, to millstones powered by water wind and perhaps in isolated cased
by
horse or oxen power. Some of the early colonists did however bring small
quern
type mills with them from Europe and there were possible a few querns
fashioned
by the settlers in North America before power mills were erected. From the quern was developed the millstones that have been used in power
driven
mills for hundreds of years. The principle of the upper stone revolving,
the
runner, and the lower stone stationary, the bed stone, was the method
most
commonly used. One of the variations is, the upper runner mill, in which,
the
upper stone is suspended in a fixed position in a wood or iron frame.
The lower
stone revolves keyed or fastened into a spindle, which is adjustable
vertically
so as to determine the texture of the meal as in the application of the
upper
runner mill. Another type of grain grinding machine is fitted with vertical
stones. This machine was developed to a high state of perfection in the
late
19th century, the frame of these mills is often made of cast iron. The
stationary stone is in a fixed position, the runner stone is keyed to
a
horizontal shaft which is usually driven by flat belt drive. The drive
shaft is
adjustable end ways by a hand wheel on a screw attached to a thrust bearing,
this alters the space between the stones so that the particles size of
the
ground product can be varied. The thrust bearing is spring loaded, this
allows
the stones to open, should any foreign bodies, such as pieces of tramp
iron,
enter with the feed, thus preventing damage to the stones. The two stones
are
enclosed in a round case, almost like the a drum, the grain is fed in
between
the stones through a hole in the upper center part of the stationary
stone. The
meal emerges from the periphery of the stones and falls out at the bottom
or
side of the drum like case down an attached spout. The runner stone has
flat
iron sweepers fitted on its edge, these have a two fold purpose; to keep
the
case clear of ground meal and to balance the stone.
In all the early mills, the material of the millstones depended on whatever
hard
stone could be obtained locally. Transport of heavy stones was, of course,
difficult, so that any suitable local stone was used. The Romans seem
to have
been the first people to move stone for milling purposes an y great distance.
From the well known Andernach quarries in the Rhine Valley, Germany,
the Romans
shipped quern and mill stones to most parts of the European Continent.
This
stone is a blue black lava, commonly called "Cullin" stone.
Cullin is a
corruption of the name of Cologne, from which city this stone was shipped
down
the Rhine. The millstones produced from Andernach stone, were called
Blue
Stones, Rhine stones, Cologne stones and Holland stones. Quarries in
Germany are
still producing millstones at the present time. The best and most popular stone ever discovered for grinding wheat into
white
flour is the French Burr. This stone is a freshwater quartz and was quarried
at
La Ferte sous Jouarre near the town of Chalons in the Marne Valley in
Northern
France, the stone from this district became world famous. The remarkable
thing
about this stone from La Ferte sous Jouarre was that it was only found
in small
pieces ranging from about 12 to 18 inches long, from 6 to 10 inches wide,
by 5
to 10 inches thick, usually embedded in layers of clay. There were sometimes
pieces of a larger size, but none large enough to make a complete millstone
of
the usual size 4 feet to 4 feet, 6 inches diameter, so that the French
millstone
of popular size, had to be built up. One reason why French stones were
so
successful was their high percentage of porosity. Some pieces were simply
a mass
of porous cells and as the stones wore away, new cutting edges appeared
which
could be worked without being refaced or redressed. Other pieces of La
Ferte
sous Jouarre stone were extremely hard and of close texture. The more
porous
pieces of stone were often light brown in color and called "nutmeg" burrs.
The
hard, close textured pieces were usually of lighter color and called "white"
burrs. French stones produced a whiter flour from wheat because the extremely
hard nature of the stone was far less abrasive than any other stone used.
An
abrasive stone tends to shred the outer part of the grain of wheat, the
bran,
into a powder. This fine powdered bran dresses through the fine mesh
silk or
woven wire of the flour dressing machinery or bolters together with the
white
part of the wheat meal and the flour thus produced is of a darker color.
In the heyday of millstone milling, there were hundreds of firms of
French
millstones makers, and these people imported vast quantities of the La
Ferte
sous Jouarre blocks of stone into their respective countries. Even today,
it is
still possible to have new French millstones manufactured. The process
of
building the complete millstones from the blocks of rough stones, begins
with
selecting suitable pieces so as to form, usually two concentric rings
looking
rather like keystones of an arch. The number of sectional pieces used,
varies,
depending on the size of the blocks; some French millstones have as many
as
nineteen sections, while there are others with as few as four sections.
Where
there are two rings of stone sections, a good millstone maker will select
the
harder burrs for the outer ring and the softer burrs for the inner ring.
This
selection of stone is to allow for the extra wear on the outer ring as,
of
course, the periphery of the runner stone travels much faster than the
center
and also covers a larger area of grain or material contact. Apart from
this
obvious consideration, the area round the center of the stone, the eye,
has to
be slightly farther apart than the outer edge of the stones to allow
the grain
to enter between the stones. This "dishing" of the stones was
also known to some
millers as "bosoming." The sections of the stone are trimmed
and dressed so as
to be a good fit and form a perfectly round, solid millstone. The runner
stone
has a round hole in the center, usually about 10 inches diameter to form
the
eye, through which the grain is fed. The bed stone is built with a square
hole
in the center about 10 inches across, this is to accommodate the neck
bearing of
the driving or balancing spindle. The pieces of stone are cemented or
plastered
together and bound with iron bands to prevent bursting when the millstones
are
in use. These bands are usually "sweated" or shrunk on, this
is to say, that the
iron bands are heated to a red hot condition and thus expand. In this
red hot
condition the bands are driven over the edge of the stones and as the
bands cool
they contract to become extremely tight. The top of the runner stone
is usually
finished off with a layer of plaster of Paris, which is sometimes mixed
with
small pieces of stone and smoothed off to form a slightly convex top.
This
plaster of Paris finish also helps to increase the weight of the runner
stone
and is a saving in cost of the expensive imported stone, if this has
to be used
to increase the weight. When new, a French runner stone of 4 feet to
4 feet, 6
inches diameter is usually about 12 to 15 inches thick at the circumference,
which is known as the "skirt" of millstones, and 15 to 18 inches
thick at the
eye or center. The weight of these runner stones is upwards of 2,400
pounds. To
balance the runner stone when pivoted on top of the spindle, pieces of
iron or
lead are driven or fastened in appropriate points so as to correct the
balance.
From about the early nineteenth century, some makers fitted balance boxes,
usually four in number which were let into the top of the runner stone
at
opposite points near the rim, weights could be placed in these boxes
to correct
the balance. In England, a firm of millwrights, Messrs. Clark and Dunham,
patented a special cylindrical balance box which carried lead discs on
a screw,
these discs could be screwed up or down to balance the stone on both
its
vertical and its horizontal axis.
The French bed stone has the underside smoothed off to a perfectly level
finish
with a layer of plaster of Paris, so that the stone will lie flat on
its base.
To correct any uneven wear, the bed stone would be leveled by using wooden
wedges driven under the stone in the appropriate spots. In late nineteenth
century mills, bed stones were often set in cast iron "pans," in
the base of
these pans, usually at four opposite points, were set pins which were
adjustable
to correct the level of the stone.
In England, in southwest Yorkshire and the northeastern perimeter of
Derbyshire,
was found an excellent rock for manufacturing millstones. This type of
rock is
appropriately known as Millstone Grit. Known to British millers as "Peak" or
gray stones, they were widely used in the grain milling industry until
about
sixty years ago. However because of their abrasive nature they were not
too
suitable for producing white flour from wheat. Quite a number of Peak
stones are
still at work in the British Isles at the present time, some for grain
milling
and others are used for special purposes, such as grinding material for
the
chemical and paint industries. After French millstones became so popular
for
flour milling, the Peak stones were used for grinding coarse grain for
animal
feeds, shelling barley and hulling oats. Peak stones were exported to
several
countries, including the U. S. A. Today, there can be seen hundreds of
complete
and incomplete Peak millstones scattered about near the old quarry workings,
which are mostly situated in desolate moor land districts.
In the United States, the early mills were mostly equipped with stones
brought
in from Europe. The Cullin stones were very popular, there are many examples
of
these millstones at early mill sites, particularly near the eastern seaboard.
French millstones were used throughout the U. S. A. manly for grinding
wheat
flour and corn meal particularly after about 1750. There were many firm
engaged
in importing the blocks of the French stones, and making these blocks
into
complete millstones, was, for many years, an extensive industry. The
advertisements by some of these millstone makers, in the American milling
trade
journals, claimed that they had their own men in constant attendance
at the
quarries in France. By having this personal supervision over the quarrying,
the
makers stated that, only the very best quality burrs were selected for
use in
their millstones. A few of the firms engaged in building French millstones
in
the U. S. A. are listed as follows:
In 1774. James Webb, Little Queen Street on the North River, New York
City.
1791. G. Speth, New York.
1796. Samuel Wilson, 40 Cortland Street, New York City.
1797. Oliver Evans, 126 South Second Street, Philadelphia, Pa.
In Leffel's
Illustrated Milling & Mechanical News,
January 1876, there were
advertisements by the following millstone makers:
Edward P.
Allis & Co., Reliance Works, Milwaukee,
Wisconsin.
Samuel Carey, No. 7 Broadway, New York City.
William H. Dillingham, 143 Main Street, Louisville, Kentucky.
Nordyke,
Marmon & Co., Richmond, Indiana.
Straub Mill Company, Cincinnati, Ohio.
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