An embalming plaque of wax

As time went by, they modified their recipes, choosing those with the best antibacterial properties.

The study was carried out by two chemists at Bristol University, UK, on mummies spanning 2,300 years of Egyptian history.

A variety of natural substances were found, some previously unreported.

"The presence of plant oils (and to a lesser extent animal fats) suggests that they were key ingredients in mummification," say the researchers, Dr Richard Evershed and Dr Stephen Buckley.

"[They] were probably used as a less-costly base with which to mix and apply more exotic embalming agents to their bodies and or wrappings," they report in the journal Nature.

Entering afterlife

Mummification was developed because the Egyptians believed no-one could enter the afterlife unless the most important part of the spirit, the "ka", could return to the body.

The dead body therefore had to be protected from decay and preserved in a recognisable form.

After centuries of experimentation, embalmers learned to remove decay-causing organs and treat the body with substances such as salts, resins, cedar oil, gum, honey and bitumen that had drying and anti-microbial properties.

It appears that fashion and cost may also have influenced the choice of materials.

"Wealthy Egyptians may have deliberately chosen the more expensive embalming fluid to impress family and friends, just as well-to-do people today select exotic woods and metal trims for their relatives' coffins," says Sarah Wissemen from the University of Illinois, Urbana, US, in an accompanying report.