Glass objects seem to disappear when placed in cooking oil.
For this activity, the temperature-resistant glass must be absolutely clean. After you have thoroughly washed and rinsed the small glass container with soap and water, you might need to give it a final rinse or two. Any spotting left on the glass will create telltale indicators of the invisible glass.
Scientists coined the word refraction to describe the bending of light as it passes from one medium to another. You probably have experienced the refraction of light reflected off objects submerged in water. Since the index of refraction of the oil is very nearly the same as that of the temperature-resistant glass, light is not significantly refracted as it passes from the oil through the glass, making it invisible in the oil. Common glass has a different index of refraction than the oil and therefore is slightly visible when submerged in it. Scientists often use refraction as a method of identifying the brand or composition of unknown glass.