Making bouncy balls from a science kit

Hi everyone,

In this tutorial, I am going to tell you the steps that my 8-year-old cousin Natalia and I took to make some bouncy balls from a science kit that she was recently given.

First of all, I am a doctor in chemical sciences, so I love these science kits and my cousin, who is my profession, always wants us to make them together because I explain to her what happens during the process from a didactic point of view.

Materials needed

• Bags of orange, green and blue crystals.
  These sachets contain crystals of sodium borate, NaB(OH)4 with some glue such as polyvinyl acetate, polyvinyl acetate or poly(ethyl ethyl ethanoate), which are the most typical glues.

• Mould for the ball

• Water

Step 1: Filling the mould

To make the bouncing ball, first add the coloured borax crystals to the mould, taking care not to overfill the mould and giving it a few taps to ensure that the crystals are well embedded.

Step 2: Dipping in water

To ensure that the borax reacts with the polymerisation of the crystals, the mould with the coloured powders inside must be immersed in water.

In this way, the sodium borate reacts with the polymerisation of the crystals to form a very elastic and malleable branched polymer.

In our case, we left the mould submerged for 10 minutes to achieve complete polymerisation.

Step 3: Removing the mould

The next step was to remove the ball from the mould.

We need to be very careful here as the ball will still be soft and we could deform it if we press too hard as the polymer will still be highly hydrated.

Step 4: Drying

We left the ball to dry for 30 minutes and noticed that it was partially hardened and the ball was bouncing.

Step 5: Further drying

To make the ball harder, we left it in the sun for two hours to dry completely, resulting in a consistent, non-deformable ball that bounces very effectively.

As a photography enthusiast, I also couldn't resist taking some macro shots to try and see those striking crystals on the surface.

I hope you enjoyed it and that it gave you an idea for a fun time with the kids making bouncy balls, because even if you don't have the science kit, you'll need the same ingredients:

• Sodium borate
• Water
• Liquid glue
• Moulding by hand
• Drying

Kind regards.