This famous Ancient Egyptian painting on Pharaoh (more accurately, Nomarch) Djehutihotep’s tomb (c. 1880 BCE) entered many tribology textbooks as possible evidence of the use of lubrication in Ancient Egypt. Engineers are quite enthusiastic, although Egyptologists are much more skeptical. A recent PRL article came to my attention, in which its authors discuss the effect of water on sand. A moderate amount of absorbed water creates capillary bridges between sand particles, and sand becomes much stiffer (e.g., you can build a sand castle of wet sand). This can also reduce the friction of wood upon wet sand in comparison with the friction upon dry sand.
A. Fall et al. “Sliding Friction on Wet and Dry Sand,” Phys. Rev. Lett. 112, 175502 (2014)
The Egyptians were pulling their sled through desert sand, which is very polydisperse. On such polydisperse sand the addition of a small amount of water reduces the pulling force by almost a factor of 2, according to our measurements. Our measurements in fact span a similar range of stresses as the Egyptians; an estimate of the maximum load they pulled is one ton per square meter or 10 000 Pa. We put up to 20 N on roughly 80 cm2, so we get to 2500 Pa, of the same order of magnitude. As for the archeologists, some have interpreted the pouring of the water in front of the sled as being purely ceremonial, which does not seem a correct interpretation in view of the results presented here… A friction coefficient of 0.33 was estimated, on the basis of the maximum pulling strength that the ropes were able to sustain.
The claim made it to the Washington Post and eventually to Wikipedia (from where I took the image above, you will see that the image is far from authentic):
Terrence McCoy (2014-05-02). “The surprisingly simple way Egyptians moved massive pyramid stones without modern technology” Washington Post.
“Bonn wrote in an e-mail to The Post. “In fact, Egyptologists had been interpreting the water as part of a purification ritual, and had never sought a scientific explanation. And friction is a terribly complicated problem; even if you realize that wet sand is harder — as in a sandcastle, you cannot build on dry sand — the consequences of that for friction are hard to predict.” He said the experiment not only solved “the Egyptian mystery, but also shows, interestingly, that the stiffness of sand is directly related to the friction force.” In all, the scientists say, “the Egyptians were probably aware of this handy trick.””
It is a very important observation, that wetting sand can reduce friction, in some cases even by half. However, the problem with the claim is that (1) the painting may be the pure imagination of an artist rather than a realistic description of any existing technology, (2) there is no evidence that the sledge moved “upon sand through desert,” (3) pouring liquid is obviously a ceremonial act, like fanning the burning incense in honor of the statue, which is also shown on the same painting (according to Egyptologist Newberry, who first studied the painting).
Below is what I wrote in my article ten years ago:
M Nosonovsky “Oil as a lubricant in the Ancient Middle East” Tribology Online 2 (2007), 44-49
The second evidence is the water lubrication allegedly used for transportation of heavy stone blocks, as shown in paintings from Saqqara and El-Bersheh, and it is even more questionable than the first one. The painting from the tomb of the Great Chief of the Hare Nome Tehuti-Hetep (or Djehutyhotep) in El-Bersheh (circa 1880 BC) shows transportation of a huge statue by many men (Fig. 1). D. Dowson (1998) writes:
“A most interesting feature of this painting is that it shows an officer standing in front of the pedestal pouring lubricant from a jar on to the ground immediately in front of the sledge. Sir A. H. Layard states that the lubricant was probably grease, but the scant archaeological evidence offers little support to this view, and others have described the lubricant as water… I am inclined to agree with the view that water was used as the lubricant, since the firmest evidence comes from the translation of the inscriptions on the wall pictures from El-Bersheh. Newberry recorded the following inscription related to the three men with yokes and jars: “carrying water by [men of] the house of eternity”.
Newberry also wrote: “… Another figure standing on the base pours water from jar in front of the sledge, perhaps only the ceremonial act, since even in large quantities water poured upon the ground could not assist the dragging.”
Interestingly, W.F. Parish, who was an engineer and not a historian, assumed that the liquid jar shown in the El-Bersheh painting contained “dark-green oil”, while the “extra men are shown with shoulder yokes suspending other vases with the days supply of oil”.
This contradicts the historical data that olive oil was practically unknown in Egypt during that period, and Dowson does not consider this possibility plausible. Then he argues, that “the sledge was drawn over wooden planks lubricated by water”, and that the man pouring water is “the first recorded oiler, greaser, lubrication engineer or tribologist”. Later he refers to an even earlier painting from Saqqara (c. 2400 BC) of transporting the statue of Ti, which has a similar motif of a man pouring liquid from a jar in front of the sledge, as an image of “the earliest recorded tribologist”.
In an attempt to further support his claim, Dowson (1998) makes a remarkable calculation. According to him, the painting from El-Bersheh shows 172 men who, assuming average force of a slave as 800 N, could achieve total drag force of 172 x 800 N = 137.6 kN. Assuming (quite arbitrarily) the weight of the colossus 600 kN, he then calculates the coefficient of friction as μ = 137.6 / 600 = 0.23 and compares it with that of wet wood-on-wood (μ = 0.2), concluding that “the sledge was indeed sliding over lubricated planks of wood”.
Of course, it is a bit naïve to assume that the painting shows the exact number of workers dragging the statue. For comparison, the painting from Saqqara shows a much smaller number of workers (in fact, only three men are shown, which would result in an unrealistically small value of μ even if modern lubricants were used). Furthermore, it should be kept in mind that tomb paintings and inscriptions are usually sacred in their motifs, and pouring liquid had a ritual or ceremonial meaning in many cultures, so the words “carrying water by the house of eternity” can hardly be interpreted as a direct reference for water lubrication. Moreover, there is another man shown in the same painting, holding a censer and fanning the burning incense in honor of the statue, which of course is another ceremonial act. While Newberry and other Egyptologists tend to consider the El-Bersheh motif as a ceremonial act, engineers enthusiastically claimed that it depicts lubrication.”
The actual image looks a bit different from what you see in Wikipedia. The painting was vandalized and partially destroyed in 1890; all the existing drawings are based on a single photo taken in 1889 by a Major Brown. This is artist’s rendering based on an old black-and-white photograph:
And this is the actual image today:
Please see also https://osirisnet.net/tombes/el_bersheh/djehoutyhotep/e_djehoutyhotep_02.htm
This is a funeral chamber, and purification of the deceased with water is a recurring motif in both inscriptions and paintings from the tomb. The term “a House of Eternity” (per-zet or per-djet) is an euphemistic name of a tomb (compare also with Hebrew בית עלמין “a house of eternity” = “a cemetery”). Therefore, the men of “the House of Eternity” who carry water (mu) are hardly “first lubrication engineers” as Dowson suggested. They are perhaps priests responsible for the purification of the body before entering its eternal dwelling place.
Below is also a description from Newberry, Percy E. [Editor] El Bersheh (Band 1): The tomb of Tehuti-Hetep — London, 1895, page 20
I went even one step further. I found the original publication by P. E. Newberry and the photograph, which he used to read the inscription. This is because you cannot see the hieroglyphs of interest (“water” and “house of eternity”) in recent pictures. Below you can see them.
This discussion demonstrates that it is very difficult sometimes to draw the line between ritual and technology when dealing with an ancient culture. Pouring water for the House of Eternity is definitely a purification ritual, but what if it also to some extant reduced the frictional resistance?