Humans yearn for definite truths, yet they are not always possible to find. We want t0 be able to hold a piece of wood or an oil and with absolute certainty give our analysis. The reality is as with many things, such certainty does not exist by simply engaging our senses regardless of who you are.
We accept the fact that humans are not perfect, there are bits of that imperfection, the 'human element' in all the things that we do. When the human element is involved and in oudh, many elements influence the 'testing', from what you ate, to the weather, all of which can throw off the accuracy of a humans assessment. That being the case we then need to introduce some scientific testing aids, such as GC and GCMS etc to assist the nose. A persons experience and nose will help them go a long way in identifying if a oil is good quality or bad, pure or not pure. However it can't discern the exactness in quantity of adulterant, or other factors. Unfortunately there are people who claim that they are able to analyse down to a part in million, including who touched the oil. People who claim such, add to the fiction and hold the oudh community back from progressing towards objective.
Using our senses there are tips and pointers that one can look out for but they are not bullet proof. However combing the nose with scientific means does make the assessment much more bullet proof.
For a sensory assessment of an oil one can lookout for the following;
Colour - every oil has a natural colour, the natural colour of the oil is different to added colour. The difference being if the oil is applied to a piece of cotton then let 'dry' the adulterated colour will stand out on the cotton rather than spread like an oil stain.
Texture - is another of the physical signs if the oil has been adulterated. If the oil is sticky to the extent if rubbed between two fingers the fingers stick, this indicates interference in the oil. If the oil feels grainy like the feel of kerosene then that is a sign that those oils have been stretched.
Cotton Test - if you apply a dot on pure cotton and leave it for a few hours and return, this is the simplest way to pick up chemical adulterants, the adulterants will usually stay on the cotton as dominant non progressive scent. If the adulterant is another essential oil, then this will require a level of understanding of different scents from essential oils.
A good oudh can last on cotton for 3-4months and the scent will keep evolving.
water test - in a test tube if one part oudh oil and ten parts distilled water, then given a good shake, what should happen is the water should go milky-cloudy, then when rested and slightly warmed up the oil should split and rise to the top. If adulterants are in there they will remain in droplets when shaken. This test will require knowledge of type of extraction used, because if the oil has been extracted from resin, by cycling-fraction-multi-step etc, then resin will also behave in a similar manner i.e form droplets.