Naked Science Forum
General Science => General Science => Topic started by: Simulated on 09/03/2008 19:01:24
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When you take water and rub it over wood, or just about any surface for that matter, why does it look better then it does after it dries? It looks darker and it looks just great. So why's that?
Thanks Sim :)
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I prefer dry wood. I can digest it easier.
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I think the water brings up the grain of the wood..
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Yeah since you're a beaver and all. Ha.
Ah I see thanks Karen.
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When you take water and rub it over wood, or just about any surface for that matter, why does it look better then it does after it dries? It looks darker and it looks just great. So why's that?
Thanks Sim :)
Because a layer of water reduces the difference between wood and air indexes of refraction so the wood's (or other objects) surface reflects light less and this increases the contrast.
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Thank you lightarrow :)
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This is a question for Edwood Woodwood.
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This is a question for Edwood Woodwood.
Or Leslie Ash
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it's a little like Basecoat and Clear finishes in the car trade. Basecoat is mat finish and when the laquer is applied we see the familiar metalic finishes on vehicles today.
Applying water to wood changes the colour by adding depth. So does applying Laquer, it adds depth to the eye. So maybe the colour of the wet wood changes the way light reflects from the surface as Lightarrow suggests?
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it's a little like Basecoat and Clear finishes in the car trade. Basecoat is mat finish and when the laquer is applied we see the familiar metalic finishes on vehicles today.
Applying water to wood changes the colour by adding depth. So does applying Laquer, it adds depth to the eye. So maybe the colour of the wet wood changes the way light reflects from the surface as Lightarrow suggests?
I assume it's the same with polish?
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Assuming that dry wood does little to reflect light and polished wood reflects light reasonably well, then polished wood should do the same as water and laquer. It might also be that light refracts through the wettened wood sending it in many different directions rather than simply bouncing off more uniformely from an untreated wood, which is lighter in colour ofc.
Thought. Cloudy sky prior to rain. Darkened sky as rays from the sun are prevented from reaching our eyes after bouncing off objects. Wood would absorb water at considerable depth. Deep water also blocks out rays and changes colour. Sorry just thinking aloud Doc
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I think it's the difference between specular reflection from the flat varnished surface (mostly you don't see an image of the light source-so the surface looks dark) and diffuse reflection from the dry , rough surface (whatever direction you view from, you will get some reflections from the light source so it will look light).
A wet surface will tend to be somewhat like a varnished surface - just not quite as flat. You can see a wet surface look paler and paler as it dries and the microscopic bumpy bits emerge above the water surface.
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There are probably several effects in play. I think the dominant one is that the structure of wood means that you don't generally get to see its colours properly.
Wood is made of dead cells and these (together with the pores between them) are filled with air. There's a big difference in refractive index between the air and the cellulose/ lignin from which the wood is made so most of the light is reflected before penetrationg far into the wood. Filling the holes with water reduces the difference in the refreactive index so the light gets further into the wood before being reflected. That way it can carry more information about the colour of the wood (effectively because it "sees" more timber).
In the same way wet cloth generally looks darker (and more transparent) than dry cloth.
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Thanks for you answers guys :)
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'Brushed' or scratched metal looks pale / silver, etc. whilst highly polished surfaces look dark, unless there is a specular reflection from a light source. I seriously think that a flat surface coating of water will have this effect of promoting specular reflections and suppressing diffuse reflections.
The effect of refractive index (quoting B-C) is fair enough but it relies on a fair thickness (i.e. several) of transparent layers; wood is fairly opaque, isn't it?
Filling the holes with water reduces the difference in the refractive index so the light gets further into the wood before being reflected.
Perhaps you should add the notion of light being absorbed by the pigment in the wood, rather than being reflected.
You must be right about several effects being involved, B-C.
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"wood is fairly opaque, isn't it?"
yes, but cellulose and (to an extent) lignin don't absorb visible light. It's only opaque because it's reflective.
If the light gets reflected before it penetrates into the timber it doesn't actually travel through a lot of wood. So it can't be absorbed by the coloureed stuff. If the wood's wet then the light doesn't get reflected so strongly at each "layer" so more of it gets deeper. Since more of it gets into the wood more light can be absorbed.
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OK, seems a fair enough argument- particularly as darkness seems proportional to dampness.