Colchester Archaeological Report 2: The Roman small finds

CATEGORY 6: OBJECTS EMPLOYED IN WEIGHING AND MEASURING
SCALES
Descriptions of the use of both the balance and the
steelyard can be found in Kisch 1966, 26-52 and
Liversidge 1973, 176-7.
Balance (scale with beam arms of equal length;
libra) (Fig 103; 2507)
2507 Fig 103 SF LWC 453(C), B165 F70. Cellar backfill. Period 5.
The arm of an equipoise balance with a central pierced lug
for suspension and pierced decorative terminals for
attaching the scale pans. Each half of the arm is graduated
by eleven punched dots into twelve divisions, each division
probably representing one ounce, uncia (27.29 gm). The
balance could therefore be used with a rider-counterpiece
suspended on the various graduated spots along the arm as
well as with weights in the scale pan (Kisch 1966, 36, 66).
Length of the arm 253.0 mm. A complete balance with pans
is illustrated in Ward-Perkins and Claridge 1976, catalogue
no 249.
Steelyard (scale with beam arms of unequal length;
statera) (Fig 104; 2508)
2508 Fig 104 SF BKC 3463(C), J275. On floor of building
destroyed in AD 60/1. The arm and scale pan of a steelyard,
total length 215.0 mm. The chains probably used to suspend
the pan from the arm are missing, as is the counterweight.
The pan was suspended from the very end of the thick part of
the arm, and the counterweight moved along the points of
the graduated scale until equilibrium was achieved, ie when
the weight suspended times the distance along the arm
were equal to either side of the fulcrum. This example, as is
usual, has two suspension hooks providing two different
fulcra, each with a corresponding scale marked on the arm
(see Kisch 1966, 66). The scale on the face corresponding to
the hook furthest in from the pan's suspension ring is
divided into six by slight transverse grooves, each length
thus given then being subdivided by eleven punched dots.
Each groove represents a pound, libra (327.45 gm) and each
dot an ounce, uncia (27.29 gm) of which there were twelve
to the Roman pound. Below this scale, opposite the sixth dot
of each pound, is inscribed an S formed by two crescents,
representing semis, or six ounces (163.73 gm) (ibid, table
12, chart 9). The other scale is less well preserved, but would
appear to be marked out with a combination of transverse
grooves and Roman numerals. (Numerals were used to mark
the scales on a steelyard from Pompeii (Ward-Perkins and
Claridge 1976, catalogue no 248), and a combination of
numerals, grooves and dots defined one of the scales on a
steelyard from Richborough, Kent (Henderson 1949, pl 38).)
Despite the poor condition of the scale, it is possible to
deduce the unit of measure involved and the minimum and
maximum weight represented at each end.
Fig 103 Balance arm (1:2)
99
The fulcrum provided by the outer hook on a steelyard
involves the measuring of much greater weights than does
that provided by the inner hook. It was usual for this greater
scale to take up more or less where the lower scale left off
(ibid, 131; Ward-Perkins and Claridge 1976, catalogue no
248). Therefore with a measure from 0 to 6 pounds on the
lower scale, the first stop on the greater scale should
represent 6 pounds. That this is so can be checked, for if the
first stop represents 6 pounds and if each subsequent stop
represents a pound, then the distance between the first stop
and nought, ie the centre of the fulcrum, should be
equivalent to that of six of the units marked on the arm. This
is indeed the case. Each unit (ie each pound) in the greater
scale measures approximately 5.0mm. The distance from
the centre of the fulcrum to the last transverse groove
marked on the arm is about 200.0mm, therefore up to 40
Roman pounds (just over 28.5 modern pounds) can be
weighed using the outer fulcrum, and the stops marked on
the arm ran from 6 to 40 pounds at one pound intervals.
Traces of Roman numerals can be distinguished at intervals
along the scale. However, apart from the row of three Xs
(possibly with other numerals) near the end of the arm, the
mid point of the central one of which lies at the point for 35,
there seems to be no correspondence between the
numerals and the more obvious divisions of the scale, ie at 5
or 10 pound intervals.
On the thin edge of the thick part of the arm uppermost when
the 6 to 40 pound scale is in use, traces of other letters or
numerals are visible. Nearest to the outermost hook is a
letter or numeral C (on its back in the illustration) and a
transverse groove. At least three other Cs can be
distinguished. As the other faces of that part of the arm are
blank, this is unlikely to be a decorative feature, and could be
expected to relate in some way to the scale, though how has
not been established.
The scale pan (found close to the steelyard arm) has a central
perforation 5.5 mm in diameter. The rim of the pan has been
folded over and there are two slight grooves round the
outside of the pan below, and at intervals equivalent to, the
depth of the fold. These grooves show through the metal on
the inside of the pan. The roughly-made rim makes it
unlikely that the pan was cast. Either spinning or turning
(Hodges 1976, 74-5) seems to be indicated. Riveted to the
pan at slightly unequal distances are three fittings (similar to
harness strap-loops, Fig 149). Each fitting has a penannular
ring passed through it which would have connected the
chains or threads used to suspend the pan from the arm. A
similar ring is fitted through the suspension hole at the end
of the steelyard arm. The diameter of the pan is
approximately 90.5 mm, its depth about 23.0 mm. Since the
pan is perforated and the steelyard could apparently be used
for large weights, it is apparent that this scale was not used
for the minute quantities involved in pharmaceutical
weighing, but for ordinary household or commercial
weighing of solid goods.