Bright and shiny - refractive index question...

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Gfamily
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Re: Bright and shiny - refractive index question...

Post by Gfamily » Thu Dec 17, 2020 12:39 am

I've had a thought that the ethanol in the gin might be giving a better liquid/glass interface - if there were any traces of grease on the inside of the glass.

I'm pretty sure it's not simply a factor of refractive index; from my old copy of the CRC handbook*, the refractive index of 40% alcohol in water is about 1.36 rather than 1.33, so I wouldn't expect that to give a perceptible difference.


* available for ~£10 on second hand sites if you're prepared to wait - every home should have one.
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dyqik
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Re: Bright and shiny - refractive index question...

Post by dyqik » Thu Dec 17, 2020 1:46 am

My tequilas are blanco unaged ones.

The strongest effects were in the oaked sweet liqueurs, so sugar (one or more of sucrose, fructose and glucose, probably) was probably the dominant ingredient after water and ethanol.

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Re: Bright and shiny - refractive index question...

Post by dyqik » Thu Dec 17, 2020 1:48 am

Gfamily wrote:
Thu Dec 17, 2020 12:39 am
I've had a thought that the ethanol in the gin might be giving a better liquid/glass interface - if there were any traces of grease on the inside of the glass.

I'm pretty sure it's not simply a factor of refractive index; from my old copy of the CRC handbook*, the refractive index of 40% alcohol in water is about 1.36 rather than 1.33, so I wouldn't expect that to give a perceptible difference.


* available for ~£10 on second hand sites if you're prepared to wait - every home should have one.
That refractive index change is how brewers, distillers, and winemakers measure alcohol content. Measuring to .2% is doable with very cheap kit.

monkey
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Re: Bright and shiny - refractive index question...

Post by monkey » Thu Dec 17, 2020 3:20 am

Gfamily wrote:
Thu Dec 17, 2020 12:39 am
I've had a thought that the ethanol in the gin might be giving a better liquid/glass interface - if there were any traces of grease on the inside of the glass.

I'm pretty sure it's not simply a factor of refractive index; from my old copy of the CRC handbook*, the refractive index of 40% alcohol in water is about 1.36 rather than 1.33, so I wouldn't expect that to give a perceptible difference.


* available for ~£10 on second hand sites if you're prepared to wait - every home should have one.
That's a ~50% increase in reflectivity for the water over the ethanol solution at the liquid/glass boundary for normally incident light (Fresnel equation, assumed 1.5 for the glass, but that could be higher, depending on the glass). This reflection is weak compared to the glass/air and liquid/air boundaries, but possibly perceptible, depending on conditions. The angles of refraction and the critical angle for total internal reflection might be different by a couple of degrees too. You only need small changes to make a difference.

Refractive index is also wavelength dependent, giving you different chromatic effects for the two things, which might be more noticeable with small differences.

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