Blue Pool - colour change phenomenon

1. Jul 27, 2009

billiards

On the weekend I visited Blue Pool in Dorset, England.

This is an old abandoned clay mine that has filled with water to produce an attractive pool. Apparently the colour of the pool constantly changes colour....

http://www.bluepooltearooms.co.uk/" [Broken]

I didn't observe the colour changes myself, but I wasn't exactly making scientific observations, the changes didn't leap out at me, they are very subtle or very gradual if they exist at all.

But why does the pool change colour at all? (Assuming that it actually does change colour.) Is the explanation of fine clay particles diffracting light a viable explanation? I can't help question that explanation because surely the clay particles would all be randomly oriented, surely you would require alignment and some kind of group behaviour to get this effect?

Can anybody out there shed any light on this for me? Perhaps its a complex dynamical effect?

Thanks

Last edited by a moderator: May 4, 2017
2. Jul 27, 2009

vin300

The braggs equation of diffraction
n(lambda)=2dsin(angle)
n is the order of diffraction, lambda is wavelength, d is the width of the grating element(distance between two particles of clay)
If the distance is of the order of the wavelength of light, different colors are diffracted differently at the plane of the particles depending on all the above factors
You see different spots at different colors, since the particles are not stationary, you see changing colors

Last edited: Jul 27, 2009
3. Jul 27, 2009

DaveC426913

Is it possible that the colour changes occur over longer times than is the assumption? It sounds like you assume seconds or minutes. Is it possible it's more like hours?

4. Jul 27, 2009

billiards

I have a problem understanding why the pool as a whole changes colour. Unless, individual bits of the pool change colour and give the overall impression of a colour change? But then why don't those small individual changes just kind of balance each other out providing an overall stationary effect?

In the leaflet I had it said the changes occured over a period of minutes. I haven't found any validation of that though, and nothing online.

5. Jul 27, 2009

vin300

Did you understand the equation?
The individual molecules in water do not change color
It's diffraction, white light that comes out of the pool and hits your eyes is no more white light because its constituents split up differently according to their wavelengths only if the clay particles are close enough to satisfy the equation(of the order of 1000 AU)
The poool would be looking colorful with different spots on the surface in different colors which change if the particles change distances or you change the line of sight.
And yes, it gives a stationary effect at one spot if the wavelengths along the line of sight give VIBGYOR, but that is not quite possible

Last edited: Jul 27, 2009
6. Jul 27, 2009

DaveC426913

You are misunderstanding. No one thinks the molecules are changing colour. The mystery is why virtually the whole pool (it seems) is acting in-concert. i.e. why would the entire pool have the separation of its clay particles change simultaneously?

I think one of the problems we're encountering in this thread is that we don't have an accurate account of what is actually observed. One critical question at least: How much of the pool changes colour? Small sections? All of it at once?

Well, at that distance, they're unlikely to be orbiting the Sun, let alone affecting the Blue Pool!

7. Jul 27, 2009

vin300

No it's Armstrong unit not astronomical unit

8. Jul 27, 2009

vin300

Small sections, every point

9. Jul 27, 2009

DaveC426913

What is an Armstrong unit?

(And why would it have the same abbreviation as another distance unit?)

10. Jul 27, 2009

DaveC426913

Do you know this? Have you personally seen it, or read an account of it?

11. Jul 27, 2009

vin300

What do yoou mean? Even if they don't the pool appears colorful.Places where the particles change position change color

12. Jul 27, 2009

DaveC426913

You are guessing. I am inquiring as to the actual observed experience.

13. Jul 27, 2009

vin300

10^-10 meters it is written as an A with a small circle above

14. Jul 27, 2009

DaveC426913

Yes, it is.

So what does that have to do with AUs (Astronomical Units) or these Armstrong units you speak of?

15. Jul 28, 2009

vin300

What happens when you see sunlight through a small gap between your fingers?It splits up That is exactly what happens here see the last part in this"[URL [Broken]

Last edited by a moderator: May 4, 2017
16. Jul 28, 2009

cristo

Staff Emeritus
You mean Angstrom, not Armstrong!

17. Jul 28, 2009

vin300

Oh sorry

18. Jul 28, 2009

DaveC426913

You fun-wrecker...

19. Jul 28, 2009

vin300

He really is?

20. Jul 29, 2009

DaveC426913

Yes. He ruined my fun.

I was teasing you about AUs and about Armstrong unit (apparently, 'Armstrong' is a common misspelling of Angstrom. Don't know why).

21. Jul 29, 2009

vin300

I'm not sure about that but you were irritating

22. Jul 29, 2009

DaveC426913

All you had to do was say 'oops, my mistake(s)'.

23. Jul 29, 2009

vin300

I change the were to are
You don't get off my head now
Stop bothering

Last edited: Jul 29, 2009
24. Jul 29, 2009

Bob S

Researchers have found that a colloidal suspension of nanoparticles of iron oxide (Fe3O4) changes colours, from blue to green to red, depending on the magnitude of an applied magnetic field. See
http://www.reactivereports.com/67/67_1.html
Here is another possibility
Titre du document / Document title
Rayleigh scattering by aqueous colloidal silica as a cause for the blue color of hydrothermal water
Auteur(s) / Author(s)
OHSAWA Shinji (1) ; KAWAMURA Takao (2) ; TAKAMATSU Nobuki (2) ; YUSA Yuki (1) ;
Affiliation(s) du ou des auteurs / Author(s) Affiliation(s)
(1) Beppu Geothermal Research Laboratory, Kyoto University, Noguchibaru, Beppu 874-0903, JAPON
(2) Department of Chemistry, Faculty of Science, Toho University, 2-2-1 Miyama, Funabashi 274-8510, JAPON

Résumé / Abstract
Thermal waters in hydrothermal ponds, bathing pools and the brines of geothermal electric power plants commonly have a characteristic blue color. Although many researchers have assumed that the blue color is due to a colloidal suspension and/or absorption by dissolved ferrous iron or by water itself, there has been no specific effort to identify the physical nature of this phenomenon. We have tested, in synthetic and natural solutions, whether aqueous colloidal silica is responsible for the blue color. Aqueous colloidal silica is formed by silica polymerization in thermal waters of the neutral-chloride type which contain initially monomeric silica in concentrations up to three times above the solubilities of amorphous silica. The hue of the blue thermal waters in the pools tested agrees with that of a synthesized colloidal silica solution. Grain-size analyses of aqueous colloidal silica in the blue-colored thermal waters demonstrate that the color is caused by Rayleigh scattering from aqueous colloidal silica particles with diameters (0.1-0.45 μm) smaller than the wavelengths of visible radiation.Revue / Journal Title
Journal of volcanology and geothermal research ISSN 0377-0273 CODEN JVGRDQ

Last edited: Jul 29, 2009
25. Jul 29, 2009

billiards

Thanks for the response. The magnetic field idea is an interseting one and one that had not crossed my mind - not least because this research is new to me. Of course, the earth's magnetic field does constantly vary in intensity on the order of tens of nanoTeslas. I think there are at least three problems here: the first is does the pool have the correct chemical conditions for this phenomenon to take place? The second is does the magnetic field vary in intensity enough for these phenomenon to take place? The third is does the magnetic field variation occur at the same frequency as the phenemon?

I don't believe that it is a scattering effect simply because as far as I know scattering is a phenomenon dominated by grain size and I can think of no physical basis for a fluctuating grain size.

Cheers