Researchers investigated the 18th Dynasty mummies of the royal architect Kha and his wife Merit, a couple who were believed to have undergone a short and poor mummification despite their relative wealth at death.
Their internal organs had not been removed and placed in canopic jars, as generally occurs in classical royal 18th Dynasty artificial mummification.
But all internal organs - brain, thoracic and abdominal organs, eyeballs as well as ocular muscles and nerves - were in excellent state of preservation after some 3,500 years.
"Elucidated 'recipes,' whose components had anti-bacterial and anti-insecticidal properties, were used to treat their bodies," the researchers added.
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The tomb of Kha and Merit was discovered by the Italian Egyptologist Ernesto Schiaparelli in 1906 on the cliffs surrounding the ancient village of Deir el Medina.
The researchers used new generation X-ray imaging and chemical microanalyses to better understand the type of mummification used to embalm the couple.
Besides the presence of the internal organs, X-rays showed that both mummies were richly decorated with jewellery, with Kha wearing funerary amulets.
Kha's external wrappings showed the presence of animal fat/plant oil mixed with a small amount of balsam, a plant gum and a coniferous resin.
The balsam and the coniferous resin, possibly cedar resin, provided anti-bacterial and anti-insecticidal properties.
Merit's embalming 'recipe' was notably different from Kha's. It consisted mainly of an unusual fish oil, mixed with a concoction made of balsam/aromatic plant extract, plant gum, conifer resin and beeswax.
The resin, and possibly the balsam, would have had to have been imported from the northeastern Mediterranean.
"Such findings don't support previous claims that the two were poorly mummified," said Egyptologist Joann Fletcher, professor at the University of York.
The mummies are kept at the Egyptian Museum in Turin, Italy.