Yes, I admit, the following stuff all sounds pretty medical. But one of the basic needs of the collector of old wine bottles is to find out more about the state of the wine inside the bottle. The problem is that you don't really want to open the bottle. Too many people do not understand the need of recorking and so they might think that an opened and recorked bottle has been tampered with. So how can you assess the condition of the wine inside the bottle without having to open it?
You will not be able to change the conditions of storing that the bottle had been submitted to before you got it. But you can take care that the bottle will be stored in the best of conditions from now on. Even though Madeira wine does not depend so much on excellent storing conditions like other wines, you are well advised to store it in a cool place with a medium humidity. Before you rest your precious Madeira bottle for the next decades you will have to check the cork. This is the most important fact that is immediately responsible for the development of the wine once it has been bottled. It is almost impossible to determine the condition of the cork's material itself without extracting it from the bottle. I have tried to asses the structure of corks still in bottles with medical ultrasound but this proved to be rather unreliable. Also you have to remove the foil or wax cover to do this. You can try to asses the cork by examining the surface of the cork, but again this means you have to remove the cover. All this alters the original state of the bottle, something you would only do if you knew you really had to recork it. What you can do however is determining the length of the cork. The longer the cork, the higher the probability that it will survive the next years without loosing its ability to seal the bottle. If you can see the cork through the glass of the bottle neck everything is fine. Taking a picture with a camera with a flash will light the cork in a good way to determine its length.
Flashed cork in a bottle neck.
But what do you do when the cork is hidden under foil, wax, paper or a straw cover? The best way then to determine the length of the cork is x-raying the bottle neck. With the right exposure it is possible to find out about the length of the cork even under a lead capsule.
It might take two or three shots to get the right exposure but I guess your bottle really doesn't worry too much about radiation. The first example below shows a very short stopper cork covered by a lead foil capsule. The second shot shows a medium sized cork covered by paper. In both examples the original state of the bottle has been maintained. And by the way: can you see the level of wine in the second picture? There are Madeira bottles so dark that it is hard to determine the level of wine in the bottle, x-rays help get the information.
X-rays of short cork under lead capsule.
X-rays of medium sized cork under paper cover.