Earlier this year, I had a look at a geological microscope. These are special microscopes with polarising filters (blocking directly transmitted light) in them, as well as having a rotating stage, so that you can easily rotate your specimen in relation to the filter (meaning different colours show up). These microscopes are usually used to examine rock and crystal samples, but earlier this year we noticed that honey seems to have this birefringent property as well.
This is what happens when something that is birefrigent is turned against a polarising filter:
Honeybees are known to use polarised light for navigation, learning during by experience the polarisation pattern of the sky. They can detect polarisation in blue and ultraviolet colours, but not in greens and yellows.
Most honey has floral residues in it by which you can detect its origin. Most commercially available honeys are a blended mixture of honeys rather than just a pure monofloral honey.
It seems that the monofloral honeys tended to have less bits of colourful pollen in it than other honeys. To extent where Acacia honey, sometimes known as false acacia as it actually comes from the Robinia pseudoacacia tree, otherwise known as black locust, doesn’t have any at all! It looks very pretty under the microscope:
This chestnut honey seemed to have these long strands in it that were equally colourful as the small bits.
This lifemel honey, a brand of medicinal bee products, had slightly more colour, but still quite sparse.
This was a blossom honey, which could have been monofloral, but was extremely pretty and colourful – very even!
Cornish wildflower honey had lots of birefringence, but it was difficult to separate the pure liquid from the chunky honey, so it was difficult to get a nice clear image.
Manuka honey from New Zealand is also a monofloral honey and is said to be amongst the best honeys in the world. If the high pollen and colour content is something to go by, that’s a good classification – as it was by far the most beautiful of them all.
But the question we had was – why would honey need to be birefringent?