Denarius: September 2018

Roman Steelyard Balance

1st-3rd century AD

I bought an interesting, and small, Roman Steelyard scale in a recent auction. It was advertised as bronze. It is not magnetic, so I assume bronze is correct. The length of the beam is 150 mm. The seller advertised it as 240 mm. It is 240 mm if you hold the scale by the weighing hook, but it is impossible to weigh items that way. “A steelyard has a beam with unequal arms. The long arm has a weight suspended from it, which is moved until equilibrium is obtained. The load is suspended from the short arm of the beam.₁” This scale has two fulcrum points, or weight ranges (low and high). Weight range is switched by rotating the load hook 180^o and using the other fulcrum point.

The scale is good but not the best design available in ancient Rome. Scale accuracy is a function of repeatable distances between the fulcrum hanger, load hanger and weight hanger. The most accurate design had load and fulcrum points in the center of the scale arm and used football shaped dowels, see pics below of my small steelyard scale and two different 19^th century scales.

The weight range of this scale is indicated by stamped dots or lines on two sides of the scale arm. I could not make a regular pattern on either side. The low weight range scale arm had 14 dots and two lines. The high weight scale arm had only two dots (that I could see for sure) and about 8 lines (again hard to see). In a flat part of the scale arm were several counter stamps. I assume the stamps were some approval of the scale’s calibration. They are hard to see in hand or in pictures, but I guess there are a dozen or more. The counter stamps are not all the same. One looks a bit like PacMan with a wide open mouth.

This scale is a plane jane version. Some scales have decorations. I thought this one might be decorated because the seller mentioned a finial. A finial is an ornament at the top, end, or corner of an object. See pic below.

I am not sure what would have been measured with a scale this size, but I estimate the max weight would be about 6 US pounds or 3 Kg. I bent the holder of a scale when I attempted to put too much weight (3 asses, or 3 US pounds, including both the weights and some Aes Rude) on a two pan balance about this size.

The seller’s description, modified a bit:

Roman Steelyard Balance. 1st-3rd century AD

A bronze steelyard with impressed point scale, two lateral chains and finial with hook, lead weight with wire hook. 29 grams total, steelyard: 24cm overall (9 1/2"). Note: the overall length is only 150 mm! The extra 90 mm is when the chain and hook are counted as length.

[2 pieces: scale & scale weight]

Condition: Fine condition.

Provenance: Private collection, home counties, UK; acquired before 1980.

TimeLine Auctions; September 4 to 10, 2018: Ancient Art, Antiquities & Coins; LOT 1217

Scale Weight = 26.38 grams

Weight Dia = 17.8 – 18.2 mm

Weight height = 16.2 mm (56 mm including hook)

Scale beam length

15.6 mm from short arm fulcrum to short end

135 mm from short arm fulcrum to long end

150 mm total length

High range scale, short distance from fulcrum hanger to hook for holding item to be weighed

15 mm from short arm fulcrum to weight hook (high weight scale)

135 mm from short arm fulcrum to long end

27 mm from short arm fulcrum to minimum weigh point of long end

Ratio = 135 / 15 = 9.0

Ratio = 27 / 15 = 1.8

Low range scale, long distance from fulcrum hanger to hook for holding item to be weighed

28.9 mm from long arm fulcrum to weight hook (low weight scale)

123 mm from long arm fulcrum to long end

27 mm from long arm fulcrum to minimum weigh point of long end

Ratio = 123 / 28.9 = 4.3

Ratio = 13 / 28.9 = 0.45

Scale Range	Minimum, with one uncia weight that came with scale	Maximum, with one uncia weight that came with scale	Minimum, with one As weight	Maximum, with one As weight
Low, long arm	0.45 uncia = 12 g	4.3 uncia = 120 g	0.45 As = 150 g	4.3 As = 1,400 g
High, short arm	1.8 uncia = 49 g	9.0 uncia = 250 g	1.8 As = 590 g	9.0 As = 2,900 g

scale in high weight range mode

scale in low weight mode, note the scale weight is just the right weight to balance the scale, some scales place a plumb bob on the scale to help detect the balance point