Rainbow Crystals

Polarized light iridizes sodium thiosulfate crystals!

15 minutes



  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
  • Observe safety precautions when working with boiling water.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

What should I do if the bottle fell out of the holder?

This likely means that the holder wasn’t fitted snugly on the bottle’s neck. Put the ring as far down bottle's neck as possible and continue.

What should I do if the Na2S2O3 solution is cloudy after 5 minutes?

At first, try repeating this step with the same bottle, but with new boiling water. Please note that the water must be boiling or, at the very least, very hot!

If after this the solution is still cloudy, then try again with another bottle of Na2S2O3.

What should I do if the solution doesn't solidify in 5 minutes?

This can happen if the solution was slightly too diluted. Press the polarizers and let stand for another 5 minutes.

I can't get the polarizer off of the cork stand. What should I do?

Don't panic! If the polarizers get stuck to the cork stand, gently pry up the bottom film. If they’re well and truly stuck, hook up with a sharp object the lower polarizer and gently lift it. Try not to bend the polarizer!

Why do the polarizers seem transparent, and the crystals dark?

This can happen if the cut corners of the polarizers don't line up. Try repeating the experiment, making sure to line up the cut corners!

Why are the crystals white?

This can happen if there was too much solution between the polarizers. Repeat the experiment, squeezing the polarizers harder.

Step-by-step instructions

Na2S2O3 pentahydrate crystals contain quite a lot of H2O molecules. If you heat these crystals, Na2S2O3 can dissolve in this water.


Na2S2O3 pentahydrate crystals possess a fascinating property–but you'll need some polarizing light filters to see it!


Apply some hot Na2S2O3 solution to one filter. Cover with the second filter.


Make sure to press the filters together to distribute the liquid evenly. This way, you'll get a nice thin layer of crystals.


Once the Na2S2O3 solution cools down, it forms crystals again. Look how cool they look through the polarizing filters!



Dispose of solid waste along with household garbage.

Scientific description

Sodium thiosulfate crystals contain five molecules of water per one unit of sodium thiosulfate Na2S2O3. Interestingly, when heated, the crystals release the water, while sodium thiosulfate dissolves in this water. This solution solidifies rapidly when cooling, forming beautiful crystals. If these crystals are put between polarizing films, they take on an iridescent sheen. This is because the polarizing films only let light with certain characteristics through, and this light in turn “iridizes” the otherwise-colorless sodium thiosulfate crystals.