How can we recreate old pharaos' perfumes? There is ongoing research where efforts were launched to find out the original constituents of a perfume for the female pharaoh Hatshepsut:



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In a perfume flask that was found in her tomb, there are apparently some remnants of the (assumed once-liquid) perfume that she used to wear. The perfume flask was sealed, so there was probably a very low amount of gas exchange taking place during the millennia that the flask took to wait for being discovered with its treasure.

However, there should still be a lot of reactions that can happen in this timescale, and since most of the reactions that just happen by themselves tend to lower energies, at some point different organic molecules would lead to the same product (e.g. acetic acid, or similar).

It seems to me, that then the only reasonable approach is to make a list of possible constituents and then start to play with the amounts thereof and model the decay reaction pathways. Then you could check if your theory predicts the experimental results.

Is this really how you find out what an ancient perfume was made of?

References:
Here, this, this one and that (talking about Tutankhamun, but the same principles would apply).
The analysis won't be done before lunch, but neither will it be an extremely difficult process.  Certainly some of the researchers will have a fragrance industry background  and access to necessary equipment like  a tandem gas chromatograph - mass spectrometer.  Also, Pharoah's perfumes were undoubtedly less complex than todays, and all oils used in perfumes are available as "known" compounds for comparison.  Additionally, all fragrances have been "fingerprinted" making identification of the compound in a sample fairly routine and straightforward.  By "fingerprinted" I mean that if a certain pattern of compounds can be detected than they will suggest the presence of a certain oil.  For example, look at lavender oil, there are about 30 chemical components in it - just like a fingerprint.

Perhaps the base solvent has evaporated through the wall of the container and oxygen has flowed into the container.  Certainly some of the ingredients will have degraded, but the container won't be full of acetic acid.  Some amount of an alcohol may have oxidized to the corresponding ketone, aldehyde or carboxylic acid, perhaps some amount of a conjugated diene may have oxidized to the corresponding dienol; but that shouldn't make the process that much more difficult.