The cream was remarkably well preserved, better than any other known examples of this age, though it gave off a bad-egg smell when the container was opened, making the archaeologists present step back for a moment.
Today, Prof Richard Evershed of the University of Bristol, with colleagues at the Museum of London, report in the journal Nature the first analysis of the rare cream, using a wide range of techniques.
They assumed it was pure fat and tried to dissolve it in an organic solvent. But half remained and X-ray analysis showed tin oxide. "I find it interesting because there are no reports of the use of tin in this sort of product from Roman times,' said Prof Evershed.
Then mass spectrometry, a method that "weighs" molecules, and other chemical tests identified that the fat came from a ruminant, probably a cow, and the presence of starch.
To create the cream required "a lot of effort", said Prof Evershed. "It is the culimination of a range of technologies and is not something you would do in your house."
The starch could have come from boiling roots and grain. The tin oxide, which is white, would have been made by oxidising tin after it had been smelted from grey-black tin oxide ore, from Cornwall. The fat would probably have come from slaughtered cattle.
He and his colleagues made their own version of what he calls "Londinium cream".
"I have a Petri dish full of it in my office," said Prof Evershed. "If you take a little out, it feels like slightly stiff Polyfilla. If you start rubbing it in, it feels greasy initially. Then as the fat gets into your skin, it gets powdery."
This powdery quality was created by the starch - still used for this purpose in modern cosmetics.
"It does whiten the skin, a slightly translucent white that can cover blemishes," said Prof Evershed. "Fashionable Roman women also aspired to a fair complexion and the Londinium cream may have served as a foundation layer."
When it was found, archaeologists speculated that the cream could have been used as face paint for religious ceremonies, or as a medicinal ointment.
Given the properties of the tin's contents, the lack of perfume, and because tin oxide has no known medicinal uses, it now seems clear it was used for beautifying the skin, said Francis Grew, the report's co-author. He works at the Museum of London, where the pot is on display.
The find was made by Pre-Construct Archaeology, which was given access to work on the site before the construction of a tower block that now contains flats, offices and a supermarket.
Roman writers reported that cosmetics and make-up were an important part of a wealthy woman's life.
Ovid wrote of beauty regimes, including depilatory creams of herbs and toners of ground poppy, moistened with water.
Mr Grew said it was not surprising that the satirist Juvenal poked fun at women who used the more unsavoury concoctions.
http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2004/11/04/ncream04.xml