Everybody is Talking About: Glass Hair

Dr Philippa Cranwell, Technical Content Creator

Glass hair is big news at the moment, and the recent Met Gala in New York put Kim Kardashian’s glass hair look right in the spotlight. But what is glass hair, how do you get it, and how does it work (scientifically)?

Image taken from OK Magazine (UK). 

What is glass hair?

According to GHD, "Glass hair is all about creating a style that's as smooth and radiant as glass catching sunlight. Imagine hair so sleek and glossy, it reflects light like a flawlessly polished mirror”. GHD also say that achieving glass hair is all about straightening dry hair in sections with ceramic straighteners and using conditioning products. And, as hair is straightened, it should be kept taught to ensure the best results. 

The dry hair aspect is particularly important, as straightening wet hair can lead to significant damage, as outlined in our recent blog post, Hair Heat Protection Claim Support 101.

How do I get it?

Most procedures for achieving glass hair recommended use of a heat protection spray before styling, as well as applying hair serum conditioning products and a hold spray afterwards. While the efficacy of heat protection sprays is a contested area, the use of conditioning products prior to straightening and a hold spray straight afterwards are likely to be significant contributors to the ‘glassiness’ of the hair after treatment. 

Why is hair shinier after conditioning and straightening?

Hair is considered healthy by customers if it is soft and shiny. While hair shine can be improved in a variety of ways, in this case the glass-like shine is probably due to the control of hair fiber alignment through straightening, as well as the application of conditioners to the hair surface. Hair fiber alignment will likely be enhanced further if tension is maintained on the tress while the straightening iron is passed over it. 

The science part

To be more technical, it’s all to do with luster. Luster is the shiny appearance of an object that is placed in the path of a beam of light and is associated with reflection of light from the surface. However, there are variations in reflectance from one surface to another. There are two types of reflectance: specular reflectance and diffuse reflectance, Figure 1. 

Specular reflectance is when light is reflected as it is in a mirror i.e. the reflected ray of light emerges at the same angle as it enters the surface e.g. light off a puddle. Diffuse reflectance is where incident light is scattered at many angles, e.g. light off a stone statue. Diffuse reflectance makes items appear dull and not shiny.

Figure 1: Specular reflection vs diffuse reflection. Image generated by Google AI.

When light interacts with the hair’s surface, there are four things that can happen: (i) specular reflectance of light from the fiber surface, (ii) transmission of light through the fiber, (iii) specular reflectance of light from the inside of the cuticle at the back of the fiber  (also known as backside scatter), and (iv) diffuse scatter from inside the fiber and the fibre surface, Figure 2.  Specular reflectance from the hair surface is associated with the white gloss bands on the hair.  Backside scatter is associated with bright coloured bands in hair, usually sat alongside the white gloss bands.  Diffuse scatter from inside the hair is associated with the background hair colour.

Figure 2: Simple model of optical processes in a hair fiber. I0 is incident light beam, ISP is the specular reflectance (mirror-like reflection of light) from the fiber surface, ITR is light transmitted through the fiber, IDIFF(INT) is where light is reflected from the fiber interior surface (backside scatter), and IDIFF(S) is the diffuse reflectance (where an incident light ray is scattered at many angles) from the fiber interior and surface. IABS and ISC stand for light absorption and scattering both when light is entering and exiting the hair. 

Making Glass hair

Technically speaking, the main drivers of hair shine are hair alignment, surface smoothness and hair colour.

The effects of hair alignment are obvious.  Super-straight and aligned hair reflects light in a uniform way.  Curly hair just reflects specs of light.  Glass hair, therefore, usually relies on a heavy dose of hair straightening and conditioning, to get perfect alignment.

Glass hair also relies on improving surface specular reflections of light.  An increase in specular reflection leads to higher luster, where something looks more shiny. Application of products, such as shine sprays, that can spread, forming a smooth surface over the hair fiber, are known to increase surface specular reflection and therefore luster. 

Finally, glass hair relies on getting the colour right.  Darker hair colours absorb more light.  The effect of this is that the surface specular reflectance appears more intense to the eye versus the diminished diffuse reflectance and background hair colour.  This is why darker hair colours appear to give more glossy shine.  On the other hand, bleached hair, absorbs less light and has more intense diffuse reflectance, and appears overall brighter to the eye.  As a result, the specular reflectance becomes relatively less intense, and blonde hair is perceived to be less shiny than darker hair colours.   

Conclusions

So, the secret to glass hair? Better alignment of your hair fibers, a smooth reflective surface coating, and a darker hair colour. Get this right and you’re ready for glass hair!

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