Puzzle jug solution? The mystery of an ancient Egyptian lamp.

Getty Museum

A "curious" type of lamp produced in Ptolemaic Egypt has caused even leading scholars in lychnology to scratch their heads over the years. The lamps are made of pottery, some examples on a wheel and some in a mould, they date from around the 3rd to 1st centuries BC and are said to be quite common at excavations in the Alexandria area.

Popularly known as 'jug' lamps, they do indeed resemble that type of object but what would be a spout is located near the bottom rather than at the top. The frequent presence of carbon residue around the 'spout' confirms that it is actually a nozzle for a wick and the object is a lamp.

But here's the conundrum that has puzzled scholars: Not only does a chamber that rises far higher than the fuel level dictated by the lowly placed nozzle seem completely pointless, the upper part of the chamber is riddled with holes. What on earth is the point of adding an apparently useless perforated extension above the fuel chamber of a lamp?

Could the object have been used as a burner to produce smoke (e.g. as insect repellent)?

No, the function I propose may have helped to discourage insects but not through the application of smoke. While carbon residue around the nozzle proves use of a flame there, that around the holes above it is merely secondary and there are no burn marks inside the vessel itself. In addition, that scenario would not explain why all the holes are concentrated in only one place.

Could the object have doubled as some kind of filter or sprinkler?

No, but it is likely that the object did perform two roles and it is those holes that give the best clue to the object's true probable purpose. While the bottom part of the chamber would have contained liquid fuel (such as olive oil) for the lamp to function, the part above the nozzle clearly did not. The contents of the upper part would need to be a relatively dry and solid substance.

That substance was almost certainly incense. Incense was used not only for religious and other formal occasions at public locations in the ancient world, it also played a traditional role in the domestic environment where it was commonly heated at household shrines, valued for its supposed medicinal properties or simply employed as an aromatic amenity.

If the upper part of the chamber was intended to hold incense, why are there no burn marks inside it?

Incense does not always need to be literally burnt to be effective. Merely heating it is sometimes a preferable alternative. Slow, gentle heating not only avoids the smell of charring and the discomfort of smoke, it releases the fragrance of the incense over a much longer period. The concept is still practised today.

How did the fuel and incense stay separate if they shared the same chamber?

It is important to bear in mind that these lamps tend to be very small (typically only 4 to 6 centimetres in diameter) and it was apparently not thought necessary - or even desirable - to create a physical barrier between the fuel and the incense. The liquid fuel would naturally sink to the bottom of the chamber and, as found in modern practice, lumps or pellets of incense heated on top of a bed of olive oil produce a harmonious aromatic blend.

Okay, so why the holes when any aroma would have vented perfectly well through the open top of the chamber anyway?

As I said, it is the holes that give the best clue to the object's probable purpose. But it is easy to misunderstand the reason for them. Confusion can be caused by incorrect assumptions about the direction of flow. I suspect the holes were not created primarily to let aroma out; they were created to let heat in.

Pottery is a poor conductor. The body of a pottery lamp does not become warm enough to have much effect on any incense placed inside it. The heat would be provided by the flame on the outside of the lamp - which is why all the holes are concentrated in only one place, directly above a scoop-sided wick-hole deliberately located as close to them as possible. The holes allowed the heat from the flame to reach the incense.

Conclusion: The objects would thus serve as both lamps and censers. Though not always immediately obvious to the modern eye, ancient technology could be quite ingenious.

RomQ Reference Collection

I was not around when the lamps were made and used, and of course my solution to their unusual form is only a hypothesis. Not quite as dramatic as solving murder mysteries perhaps but I personally find that trying to interpret the more intriguing artefacts from the past can be just as satisfying - even if my simple deductions may sometimes strike other sleuths as "elementary".