# Optical Water Prism

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## Introduction: 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 : https://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.

## Step 2: Three Rectangles ...

- Cut three rectangles of the same size.

Mine are squares of 9 by 9 centimeters, and I used a manual saw.
If you use an electric saw, be careful : acrylic glass may melt because of the friction.
Of course, it must be possible to use classical glass cutting techniques.

The adhesive tape should be inside, as you're supposed to glue the external edges.

- Glue the edges.

Be careful or you'll get leaks !

- And let it dry.

Once dry, it is possible to leave adhesive tape inside the prism. It does not really matter as long as it is transparent and don't cover too much of the surface.

## Step 3: Two Triangles ...

- Cut the two triangles that will cap your prism.

- Drill a hole into one of the two triangles.

Actually, it is possible to drill a hole in both triangles. This would help to easily flush the prism if required.
Make the hole near one of the points. This will help to easily evacuate an eventual bubble of air.

- Glue them on each side of your prism.

- Let it dry.

## Step 4: Fill It ...

- Fill it slowly with water.

I recommend not to fill it directly under the faucet (water tap). If you don't keep it dry, you may find difficult to detect eventual leaks.
You could use a funnel. If you don't have one, you could improvise one like I did.
It is also recommended to fill it with water that does not contains dissolved air (more about that in step #5).

- Plug the rubber stopper into the hole.

Try not to create a big bubble of air when doing so.

- Dry it if required, and abandon it on a dry table for few minutes to be sure there is no leaks.

In case of eventual leaks, try to fill them with glue ... Empty your prism if required ...

## Step 5: Eventually ...

Eventually, lots of tiny bubbles will appears against the inner surfaces of your prism.

They appears because of the dissolved air into the water. Patrick Pending recommend to let the water sit overnight before filling the prism with.
According to the " Make crystal clear ice ! " it is possible to get rid of the air contained into the water by boiling and letting it cooling several times.

Though, if you don't want to bother boiling water etc, I found it's possible to get rid of most bubbles (once they appeared) by shaking the prism. All the tiny bubbles will join to form a big bubble that you'll eventually evacuate through the rubber stopper.

## Step 6: Congratulations !

Voila ... It's ready for use.

Later, I will make an instructable about how to decompose light with this prism.
The pictures are ready, but it's time to sleep for me now ... =o)

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## 35 Discussions

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.

oh man i could just imagine combining this with that dudes tesla cutter to make a whirlpool inside it!

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).

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?

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

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!

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

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 ;-)

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)

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.

you know that getting a prism from a binocular is the way to go, plus you will get freebie lenses too. but you are stubborn and don't want to admit defeat, so go ahead and buy those plastic sheets and show us your skills in making giant ass prisms, 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.

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.