# Optical Water Prism

This is an optical prism made of acrylic glass and filled with water.

Despite it's far to be a perfect prism, you can use it for personal or classroom basic optical experiments.

As it is filled with water, its refractive index is of about 1.33.

If it was entirely made of glass or acrylic glass, its refractive index would be about 1.5.

Actually, in this prism, four refractions occurs :
1 - air (1.0) to glass (1.5)
2 - glass (1.5) to water (1.33)
3 - water (1.33) to glass (1.5)
4 - glass (1.5) to air (1.0)

## Step 1: What do you need ?

- a board of acrylic glass
- tools required to cut acrylic glass
- something to glue acrylic glass
- a tool to drill acrylic glass
- a rubber stopper (or anything that will do the job)
- a funnel ( see here if required : http://www.instructables.com/id/Improvised-Tiny-Funnel/ )

Note :
- It is, of course, possible to use real glass instead of acrylic glass. Though, it would be difficult to drill it.
mollster777 years ago
could i make this with window sheet glass? what is acrylic glass? where can i find it?
If you can cut (and drill) window glass, there is not problem at all I think.

Acrylic glass has various names. In my country, we generally call it Plexiglass. It's a fake glass made of plastic.

Instead of glass or plexiglass, you could make your prism with transparent CD cases if you want.
bedbugg27 years ago
i want to make one!
Me too I want to make one !! =o)
7 years ago
oh man i could just imagine combining this with that dudes tesla cutter to make a whirlpool inside it!
TKH7 years ago
Nice instructable! You could also think of filling this prism with something other than water. If you used glycerol (aka glycerin), for example, there would be little change in the index of refraction at the liquid-acrylic interface (I think the index of refraction is about 1.49 for acrylic and 1.47 for glycerol) -- one could effectively replace your 'four refractions' with two. Of course glycerol is so viscous that it might take a week to fill up the prism through a funnel that small ... :)
Thanks. =o)
Actually, I was thinking about filling it with colored water, oil, transparent shampoo etc, for various experimental purpose, but I'll wait to make some others for that ... (that could be difficult to clean).
power7 years ago
cool!!!
C-h-a-v-e-z7 years ago
dude, this is seriously stupid. building a prism from plastic stuff and gluing them and filling it with water.... couldn't you just find some old binoculars and salvaging the prisms from them?
7 years ago
This is by no means a perfect prism, mainly due to the differing refractive index of water and acrylic. However, this technique would allow you to build large prisms that would otherwise be prohibitively expensive to buy. So as an instructable I think it has real merit. Pat. Pending
7 years ago
This is not stupid by any means, in fact it was one of the principal tools that Johann Wolfgang von Goethe (1749-1832) used to demonstrate his theories on the mechanics of color, human vision and the way our brains process that information in his book, Goethe's Color Theory (1810). If you can find the book, it is totally worth reading, especially if you have a water prism at your disposal because most of the book requires a prism for the demonstrations of the theories included. Great instructable!
7 years ago
so we conclude it is a great instructable if we were living in 1810. "chooseausername" idea is only short by about two hundred years. Great Job
7 years ago
Way to show how uninformed you are lol. We still breathe air.. :O How ANTIQUATED, WE NEED TO RE RE REINVENT THE WHEEL. This is a good instructable; the internet didn't exist in 1810. The prisms in binoculars are tiny; and this is the cheapest way I know to make a pretty large prism.
dude, this is seriously stupid. building a prism from plastic stuff and gluing them and filling it with water.... couldn't you just find some old binoculars and salvaging the prisms from them?

Sure. You must be right Mister. Everyone has an old binocular at disposal ...

And every binoculars can be took apart without damaging the water proof rubber skin ...

And in case the binocular get damaged, it does not matter, because everyone has several binoculars at disposal. And if they don't, they still can buy a new one for 20 euros ...

A new cheap binocular, here, cost 20 euros.
A board of acrylic-glass, here, cost 5 euros.

The good choice is obvious ... I wonder why I'm so seriously stupid sometimes ;-)
7 years ago
you can buy used binoculars for a lot less than 20 euros. look ebay or something. i did not tell you to buy new ones. in addition, one binocular have 4 prisms inside
(I don't know where you comment is gone, but here is my reply).

you know that getting a prism from the a binocular is the way to go, plus you will get free lenses too.

I know that getting prism from a binocular is the way to go if :
- I have old binocular at disposal or if I can wait for a week for it to be shipped
- I need tiny prisms

but you are stubborn and don't want to admit defeat,

What I don't admit, it is your arrogance. Arrogance is supposed to be my specialty.

so go ahead and buy those plastic sheets and show us your skills in making giant ass prisms,

The purpose of this site is to show and teach how to make things. Don't you understand that ?
I needed to make a big prism, I made one, and I show how I did.
Now, if someone need a "giant ass prisms", this person know it's possible to make water prism.

as if somebody told you that the bigger the prism, the more easier it is to see each photon of light. you are not making a microscope you know.

I have to admit that with your telepathic abilities (as you seems to read into my mind), you must be superior to me and to the rest of the world Master Chavez. Would you like I lick your feet to show you how dutiful I am and how superior you are ? =o)
7 years ago
If I wanted to demonstrate refraction or spectral dispersion to a large group, I would use a piece of equipment just like this.

If I wanted my pupils to work with prisms in small groups, I would issue the optical prisms that we bought for less than two pounds each.

If I felt like smashing up two-five hundred pounds worth of binoculars to get a class set of prisms, that would be stupid.
myric7 years ago
Another way to cheaply separate light into bands is with a diffraction grating. A diffraction grating is much cheaper even than a prism and everyone owns a couple dozen. Pull out a CD or DVD and shine a flashlight on it. The light reflects at an angle to the incident beam and the angle depends on the color of the light. You have an instant rainbow with only a flashlight \$1.00 and a \$0.30 CD.
Yes, there is an instructable from an other member showing this technique :
http://www.instructables.com/id/Naff-Movie-into-_DVD-Spectra_/
gmoon7 years ago
For an experiment, this is rather cool....

You refer to 'refractions' twice, but they are actually reflections. Prisms and other transparent objects exhibit total internal reflection when light reaches a certain angle, relative to a surface. This phenomenon is why fibre optics work...

Refraction is the bending (changing direction, actually) of light, which your nice spectrum illustrates (different wavelengths 'bend' at different angles.)
7 years ago
No, he's right - If you're using this in the classic "Pink Floyd Album cover" set-up, then the light will be refracted four times, once at each surface of the acrylic sheets.
@Kiteman : Actually, Gmoon was not talking about the text in the intro. He was talking about the text into the first picture of the intro. The picture shows a "reflection", and I wrote "refraction". That's what he pointed out, and I corrected it ;-)
7 years ago
Refraction is the bending (changing direction, actually) of light, which your nice spectrum illustrates (different wavelengths 'bend' at different angles.)

As for the reflections, that's total internal reflectivity, like the prisms in binoculars. The light is bouncing off the refractive surface, not passing through. Some refraction is also taking place (light passing in and out of the prism), of course, but the entry and exit angles are complementary so they cancel any 'separation' fx.
7 years ago
Actually, not quite true. The internal reflectivity is distortion-free when the observer viewpoint is perpendicular to the exit face.
Thanks, for pointing it out this stupid mistake =o)
I'm going to update the instructable.
Swartzkip7 years ago
f you boil the water, than cool and boil again and than cool and fill the prism no bubbles! (got that from the clear ice instructable)