Daily Science Factlet – Glowing Glass

After a great afternoon at Bath Aqua Glass this weekend, I thought I would share some interesting glass facts that we learned there, particularly the additives that are used to create different colours.

The glass used for windows, glasses and ornaments is made by heating silica (silicon dioxide – which also makes up quartz and sand), along with other chemicals such as sodium carbonate (to lower the melting temperature) and various oxides (including calcium, magnesium and aluminium, to make the glass more durable), to around 1200 degrees C in a furnace.

Antique glass bottles, showing blue-green iron (II) oxide impurity. The darker yellow-green colour of two of the bottles is due to iron (III) oxide.

This glass can have a slightly greenish tint to it due to iron (II) oxide impurities (to see why some metal compounds can have different colours, watch my Naked Science Scrapbook on copper compounds). This colour can be removed by a combination of adding an oxidising agent, to convert the impurities to iron (III) oxide, which has a yellow-green tint, then masking this by adding small amounts of purplish and blue colour (from Nickel and Cobalt – see below).

When colouring glass, a combination of additives, oxidising agents, the temperature at which they’re heated and how the final piece is cooled affects the final colour, but here are some of the most common additives and the colours they give:

  • Chromium – The chromium (III) ion gives emerald green when added to base glass with arsenic and tin oxide.
  • Cobalt – Compounds of cobalt (II) ions give a deep blue colour when the base glass also contains potash (a mixture of potassium compounds), or pink when used with a borosilicate glass base (which is the type of very heat resistant glass used for Pyrex cooking dishes).
  • Copper – copper (II) oxide gives the turquoise blue colour of Egyptian glass, one of the first types of coloured glass to be made.
  • Gold – unlike the other colour-giving additives on this list, gold is added in its metallic form, rather than as a salt. The tiny particles scatter the light entering the glass, giving a ruby colour in high concentrations when added to lead glass with Tin and cranberry in lower concentrations.
  • Iron – Iron (II) oxide gives the green colour to beer bottles, and when mixed with Chromium, gives the deeper green glass used for wine bottles.
  • Manganese – anyone who remembers potassium permanganate from school chemistry lessons will remember its vivid pinkish purple colour. The same ion provides a purple colouration when added to glass, and was used as far back as Ancient Egypt.

An Improbable Infestation

This week I attended a book launch unlike any other. It was for Annals of Improbable Research and IgNobel Prize founder Marc Abrahams’ new book This is Improbable.

The IgNobel Prizes celebrate research that makes you laugh then make you think. Previous winners have included research that showed cows with names give more milk, and a paper that categorised the different types of belly button fluff.

This is Improbable follows in this vein – celebrating odd pieces of research from around the world. Instead of getting up and talking about the book at the launch, Marc asked several of us to choose readings from examples of improbable research that he brought with him. We had stories of the culinary merits of different tadpoles, the fight between two brothers over their bees and peaches, and how a CEO’s face shape can affect the success of his company.

I chose a paper published in 1954 in the journal Science which tells a cautionary tale from Mr Paul D. Hurd Jr. to entomologists (who study insects), entitled “‘Myiasis’ Resulting from the Use of the Aspirator Method in the Collection of Insects”. The title may not give much away, but read on for the full gruesome story…

“During the past two summers I have served as research entomologist at the Arctic Research Laboratory, Point Barrow, Alaska. Since the insect fauna is composed largely of small-sized insects….considerable use was made of the aspirator method of collecting.”

So far so normal.

“Apparently because of the use of this aspirator, a most unique case of ‘myiasis’ (or infestation) occurred.”

Ah. You may see now where this story is going. The gentleman then goes on to explain what an aspirator is…

“…An apparatus generally designed to collect insects by suction, consists of a vial into which is fitted, by means of a stopper, two pieces of copper tubing, one of which is directed towards the insect and the other is attached to a length of rubber tubing which is placed in the operator’s mouth. Across the end of the copper tubing leading towards the operator’s mouth a fine brass screen is secured.”

And now we get into the juicy part of the grim tale…

“Approximately 2 months after completion of the past summer’s work at Point Barrow I became ill. During the week following the onset of illness four major groups of insects (Coleoptera, Collembola, Diptera, Hymenoptera) were passed alive from the left antrum of the sinus [my emphasis]. These insects included three adult rove beetles, 13 fungus gnat larvae, three egg parasitic wasps and about 50 springtails.”

Yep. You read that right. This guy has written in to Science to tell them that he had insects growing inside his head after using the aspirator for 4-6 hours every day, which he suggests caused him to breathe in insect eggs that passed through the ‘fine brass screen’. Amazing. At the end of his letter, he goes on to offer advice for other entomologists so they do not suffer the same grisly shock that he did…

“Since it is likely that the aspirator will continue to be an important means for the collection of small-sized insects, I would like to suggest that those persons who utilise this apparatus so modify it that the flow of air will not be directed toward the operator’s mouth.”

He does admit that “it is almost unbelievable that the insects should have undergone several stages of their metamorphosis within the sinuses”, which I would agree with – how would you not notice? Sadly there were no independent witnesses mentioned in the paper (though a full medical write-up from Donald G. Casterline M.D. is apparently available), or any mentions of whether the incident had ongoing effects on Mr Hurd Jr.’s health.

You can also listen to my reading of this story on this week’s Pod Delusion.

Daily Science Factlet – Photonic crystal fibres

A friend and I are entering a video into the Optical Society’s Optics in a Minute video contest. We’re doing our video on photonic crystal fibres, which are allowing researchers to explore new ways of transmitting light for things like telecommunications and medical procedures.

Traditional optical fibres, that employ total internal reflection of light to carry information for things like the internet, can’t carry high powered laser light, because they would either melt, or distort the light – not great for accurately carrying data.

But unlike the solid glass traditional fibres, photonic crystal fibres are made up of a long hollow crystal of silica, so they carry the light in a different way (Fig 1). The sides of the crystal will allow certain wavelengths of light through but not others, due to an effect known as the photonic bandgap. And you can choose a crystal that reflects only the band of wavelengths you’re after (Fig 2).

This means that we can now guide powerful lasers within fibres that don’t melt and don’t distort the light.

Stay tuned for the video – we’ll put it up on youtube and I’ll post it here…

The changing (feathered) face of dinosaurs

This week, the second episode of the much-anticipated new series of the BBC’s Doctor Who saw two of the Doctor’s friends battling a group of Velociraptors on a spaceship (it’s Doctor Who, just go with it). What most excited me about this turn of events in the episode was that clearly the effects artists on the show have been keeping up to date with research on the presence of feather-like structures on dinosaurs like Velociraptor (see image).

Back in 1993, when the Velociraptors of Jurassic Park were scaring the bejesus out of kids (and adults) around the world, it was generally agreed that while species like Velociraptor were ancestors of modern birds, feathers were a classifying feature of birds as a group, and so their dino great-granddaddies didn’t have them.

The idea that birds descended from dinosaurs has been around since Thomas Henry Huxley proposed it after examining the fossils of Archaeopteryx (originally considered to be the ‘first bird’) and Compsognathus, a chicken-sized theropod dinosaur in the early 1860s, and found many corresponding anatomical features. His theory didn’t really take off however, until the discovery and description of Deinonychus (that means ‘terrible claw’ in Greek) a hundred years later. Palaeontologist John Ostrom described skeletal similarities between Deinonychus and modern birds like a fused wishbone, and similarities in the wrist and the pubic bones, which strongly suggested that birds were, in fact, living dinosaurs.

But where did their feathers come from? The place to look is the fossil record, but the problem with determining if a fossilised creature had feathers, or scales or fur, is that these features don’t tend to fossilise very well, being made of more delicate stuff than bone. This is why the ‘clever girl’ Velociraptors in Jurassic Park were shown to just have scaly skin – examples of feathered non-avian dinosaurs had simply not been found in 1993. All this changed in 1998 with the discovery of the Late-Jurassic Liaoning formation in China, and the description of two dinosaurs found there – Protoarchaeopteryx and Caudipteryx. The Liaoning formation is made up of a sediment known as Lagerstätte, a very fine-grained sediment that, conveniently, preserves features like feathers in detail (it was in this same type of sediment in Germany that the original Archaeopteryx fossil was found, along with its feathers).

This discovery was followed by many others, including the description in 2007 of characteristic quill knobs on the bones of a Velociraptor specimen, closely resembling those found in modern birds for attaching feathers.

But the question of why non-avian dinosaurs had feathers remains to be resolved. Many of them are no more than barb-like protofeathers, and their wearers could certainly not have flown. Perhaps they were for insulation – they tend to be found only in the smaller theropods, rather than the larger species like Tyrannosaurus or Allosaurus. Or perhaps they were used for display, much like the frills seen in modern lizards. This is the theory the effects artists on Doctor Who went with, showing the raptors flaring up the barbs along their back and arms when threatening Amy and Riddell.

So to what extent were species like Velociraptor covered with feathers? Did they just have a light covering of barb-like feathers (as we saw in Doctor Who), or were they larger and more extensive, like the full covering of modern-looking feathers seen in species like Archaeopteryx and Microraptor? The jury’s still out. But who knows, maybe by the time Jurassic Park IV comes out (yes, really – it’s due out in 2014), they will have given the raptors, and several of the other dinosaurs, their appropriate feathered jackets. They’ll still be just as terrifying.

Science of Food books

For everyone who came to my Bread, Brie and Booze talk at the British Science Festival, here’s the science of food books I recommended, plus the recipe for the instant homemade cheese that everyone seemed so fond of!

On Food and Cooking – McGee

The Chemistry of Food – T. P. Coultate

Culinary Reactions – Simon Quellen Field


1 pint milk, 2 tablespoons vinegar (I used distilled malt vinegar), 1/4 teaspoon salt. Mix all ingredients in a microwave-safe bowl or jug and microwave on full power for 4 minutes. Take out and stir and large clotted curds should form. Strain these out with a slotted spoon into a seive lined with several pieces of kitchen towel and drain. You will need to change the kitchen paper a couple of times, and gently pressing the cheese will get more liquid out of it.

Daily Science Factlet – crustacean colouration

Whilst chowing down on some prawns recently, someone asked me why it was that they were a blue-grey colour when raw, and a pink colour once cooked. Here’s why…

If you look closely at a raw prawn, you can see that the colouration isn’t even, but is distributed in small spots on their shell, and on the flesh underneath. The spots are made up of pigment-containing cells called chromatophores, that you can find in all kinds of organisms from bacteria to birds and plants to parrotfish. The combination of overlapping cells containing different coloured pigments gives the final colour of the organism (and making the chromatophores expand or contract is how octopus and cuttlefish are able to change their colour).

The key pigments involved in the blue-grey to red change in prawns (and lobsters) are the red astaxanthin (that also makes salmon and flamingos pink), and the blue crustacyanin. Crustacyanin is actually made up of several astaxanthin molecules tied up together with a protein molecule. In raw prawns and lobsters you have a combination of the red astaxanthin and the blue crustacyanin in the cells, giving a greyish blue.

But when you heat prawns up, the protein holding the crustacyanin together unravels, freeing up the astaxanthins. These are very heat tolerant, so just stay red on heating, making the cooked prawns look that appetising pink colour…

Daily Science Factlet – the Perfect Cheese Toastie

Sometimes nothing will do but a crispy, savoury, oozy toastie. But which are the best cheeses to use? Well, science can help you out…

First of all, to get the gooey centre, you want a cheese (or combination of cheeses – let’s go all out here) that will give a ‘good melt’. There are some cheeses that would definitely not be good for this, particularly the acid-coagulated cheeses like paneer, ricotta and cottage cheese (see my post on why they don’t melt well).

The most important factor in melting is water content. High water content in the cheese dilutes the proteins that make it solid, meaning they are more weakly bonded together and so will flow past each other and melt at a lower temperature. Moist cheeses like fontina, gruyere and monterey jack are therefore good to provide the gooiness.

Watch out for using high fat cheeses – they are more likely to leak melted fat as the protein network breaks down with heat, and can make the toastie greasy. Though to be fair, that is often part of the enjoyment. It’s not a health food.

Now to stringiness. For some, another important aspect of a toastie. The reason a cheese goes stringy is that the little balls of milk protein (called casein micelles) in the cheese get linked up into long chains by calcium.

Cheeses tend to get less stringy with age. The first reason for this is that as a cheese ages, more and more lactose sugar is converted to lactic acid. Acid dissolves the calcium holding the micelles together, stopping them from forming stringy ropes and making them fall apart and flow more easily. The second reason is that as a cheese ages enzymes start to break down the micelles into small pieces that are too small to link up into chains.

So if you’re a string fan, then cheeses like emmental, mozzarella and young-ish cheddar are good. And if you prefer just a gooey centre, just use the moist cheeses above, and maybe an aged cheddar too.