Colorful rain in a glass

Is it pos­si­ble to see rain in­doors? How about a vi­brant­ly col­or­ful down­pour? Here’s a sim­ple way to or­ches­trate a storm of col­ors even on the sun­ni­est day.

Safe­ty pre­cau­tions

• Con­duct this ex­per­i­ment only un­der adult su­per­vi­sion.
• Cau­tion, col­orants may leave marks on the skin and sur­faces.

Reagents and equip­ment

• 150mL veg­etable oil;
• liq­uid food col­or­ings;
• glass;
• glass con­tain­er;
• 500mL wa­ter;
• wood­en stick.

Step-by-step in­struc­tions

Pour the veg­etable oil into a glass and add some food col­or­ing. Stir vig­or­ous­ly with a wood­en stick. Then pour the oil and dyes in a glass con­tain­er filled with wa­ter. Give it some time…

Process de­scrip­tion

Since liq­uid food col­or­ings are aque­ous so­lu­tions, the col­ored droplets pass freely through the oil lay­er. But why ex­act­ly does this hap­pen? The molec­u­lar prop­er­ties of oil and wa­ter pre­vent them from mix­ing. Wa­ter con­sists of po­lar­ized mol­e­cules, i.e. each of its mol­e­cules has a pos­i­tive charge on one side and a neg­a­tive charge on the oth­er. As op­po­sites at­tract, the wa­ter mol­e­cules are at­tract­ed to each oth­er. The oil mol­e­cules are non­po­lar, so they don’t at­tract wa­ter mol­e­cules and there­fore don’t mix with them. When stirred, the large drops of food col­or­ing break up into small­er drops and “freeze” in the oil, form­ing an emul­sion. Food col­or­ing is denser than veg­etable oil, so when the emul­sion is in­tro­duced to a body of wa­ter, the drops grad­u­al­ly trick­le down to the oil-wa­ter bor­der. When the drops reach the wa­ter, the col­or­ful storm be­gins.