How to hide glass

How to hide glass from prying eyes

Safe­ty pre­cau­tions



  • 3 glass­es;
  • 3 glass rods;
  • glass test tube;
  • wa­ter;
  • veg­etable oil.

Step-by-step in­struc­tions

Fill the first glass with wa­ter, the sec­ond glass half with wa­ter and half with veg­etable oil, and the third with just veg­etable oil. Put a glass rod into each glass. Note that the rod dis­ap­pears in the oil!

Process de­scrip­tion

Re­frac­tive in­dex is a prop­er­ty char­ac­ter­iz­ing how quick­ly light spreads through a giv­en medi­um. Each medi­um – air, wa­ter, oil, and glass – has its own re­frac­tive in­dex, con­tin­gent on the medi­um's na­ture and the prop­er­ties of light. We can see trans­par­ent ob­jects be­cause they dis­tort or re­flect light in some ca­pac­i­ty and thus “ap­pear.” The greater the dif­fer­ence be­tween the re­frac­tive in­dices of light in dif­fer­ent me­dia, the high­er the dis­tor­tion. Glass dis­ap­pears in oil be­cause the two have very sim­i­lar re­frac­tive in­dices ​​(1.47 and 1.52), mean­ing that light re­mains al­most undis­tort­ed at the bor­der be­tween the oil and the glass. Wa­ter’s re­frac­tive in­dex (1.33) is sig­nif­i­cant­ly low­er than that of glass, and thus the glass rod is vis­i­ble in wa­ter.