Bubbles always hold the gas or liquid inside of them with the least possible surface area.  The geometric form with the least surface area for any given volume is always a sphere.

How big was the biggest bubble you ever made? Did you see rainbow colours on it? How can you make big bubbles?

Here's the bubble recipe we use at Scitech.

You will need

• Distilled H2O (water)
• Detergent (washing up liquid)
• Glycerol
• Long piece of bendable wire (perhaps you can find an old coat hanger)

What to do

• Into a big bowl or bucket, pour the distilled H2O. Stir in the glycerol and detergent. The detergent has stabilizing agents and ethyl alcohol, which are needed for good bubbles. Allow your bubble mixture set for about 30 minutes to help it thicken.
• While you wait, make a circle out of the piece of wire, leaving enough wire on one side for a handle. (You may need grown-ups to help with this.) Practice dipping the round part in the bubble mixture and see how it works best for you.

What's happening?

• Bubbles are bits of air or gas trapped inside a liquid ball. The surface of a bubble is very thin. Bubbles are particularly fragile when a dry object touches them. That's because soap film tends to stick to the object, which puts a strain on the bubble. So if you want your bubbles to last longer, keep everything wet, even the bubble blowing tools.
• As you lift your frame out of the solution, the soap film flows into a state of minimum energy. The soap film is in this state of minimum energy when it's covering the least possible amount of surface area. The intricate shapes you see inside the frame represent the minimum area the soap film can cover. You may notice that a soap film will sometimes take on different shapes when you dip the frame into the solution again and again. That's because there may be more than one way for the soap film to form a minimum surface area.
• Bubbles consist of two thin films of soap with water in between. When white light (which contains all the colours of the rainbow) hits the soap films, it will be reflected back, but is sometimes spread out into a spectrum (or rainbow). When two sets of reflected waves meet, they can add together, cancel or partially cancel each other out depending on the thickness of the film and the initial colour of the light. When light waves of a particular colour meet and cancel each other, then that colour is subtracted from white light. For example, if the red light waves cancel, then you see white light minus red light, which you perceive as blue-green light.

More bubble creation ideas

• The basic wire loop - Take a short piece of pipecleaner and form a loop in it about 4 cm in diameter. Dip into the bubble solution and gently blow.
• Drinking straws make fairly good bubble blowers. They will hold more bubble juice if 4 short slits (about 5cm) are cut at the bubble end. The resulting tabs should splay out.
• The big bubble loop - Slide two drinking straws onto a piece of string about 1m long. Tie off the ends to form a loop. Hold the straws apart to form a big rectangle. Bring the straws together to close the rectangle and dunk it into a bucket of bubble mixture. Pull it out again and slowly separate the two straws. A film should form around the loop. If it doesn't break, pull the loop through the air to form a giant bubble.
• Make frames - Form frames using the drinking straws for the straight pieces. Connect two straws at a corner by inserting a doubled-up pipe cleaner into the end of each straw. In places where three straws meet, fold the pipe cleaners three ways. Attach a pipe cleaner handle to your frame.
• Try constructing cubes or tetrahedrons, or just let your imagination run wild. Mix the soap solution in the bucket. Make sure that you have enough solution to fully cover the frames when they are dipped.
• Dip the frames into the soap solution, and observe the fascinating geometrical shapes that the soap films form.