Manufacturing Opium Weights
At all times opium weights have been cast in so called ‘lost moulds’.
Thanks to R.C. Temple’s report we know how standard opium weights were made in Upper Burma during the second half of the 19th century.
In 1888, during his stay at Mandalay, Temple had a whole set of standard weights cast. Having returned to England, Temple offered this set of weights as a present to the Pitt Rivers Museum in Oxford where it is still displayed today.
He describes the manufacturing as follows:
At first liquid bees wax is poured into two lead moulds. With the hardening of the wax the two halves were put together to form a complete figure and by the contours corrected by hand. The pedestal and the actual animal sculpture of larger opium weights were cast separately and joined together. The wax figure was thinly covered with clay, then, when dry, moulded with a mixture of clay and chaff. Having dried out, the mould was heated to melt the wax which was then drained off through tiny channels in the mould. Now liquid metal could be poured into the clay mould. When the metal was cold the clay mould was broken. The animal-shaped opium weight was finished by hand and the weight adjusted to the standard.
We still do not know when lead moulds came into use.
Apparently “duck” and “lion” standard opium weights were manufactured this way from the 19th century onward if not earlier. It is evident that standardized elephant opium weights from Laos were also produced in this way.
Before this time each wax model had to be formed by hand and it is certain that the manufacture of the rare types of weights was continued in the old manner.
Up until the last half of the 19th century weights were made of bronze, an alloy consisting of copper, tin and zinc.
The older opium weights (16th / 17th centuries), containing more copper, are of a reddish colour. During the late 17th and the 189th centuries, tin was the most prevalent metal in the alloy, giving a silvery hue. After that the opium weights were cast from a alloy with the soft yellow of bronze.
In the late 19th and the early 20th centuries, the material was brass.
The consistency of the alloy may help us to discover at what time a weight was cast, provided that other factors such as the motif, the seal or gauge mark fit the definition as well.
A brass weight, anyway, cannot be very old.
In the 14th century some weights have a stone-cored (pegmatite) base covered with a thin skin of bronze, about one millimetre thick, see this picture.