Disappearing Glassware

When Pyrex glass is placed in vegetable oil, it becomes nearly invisible because both materials have the same refractive index.

1. Fill a large clear glass bowl with vegetable oil and place a Pyrex beaker inside so it will be hidden for a “reveal” at the end.
2. Prepare three Pyrex beakers: one with water, one with water and oil (oil on top), and one left empty.
3. Dip a Pyrex test tube into water. Point out that although it is less visible, it can still be seen.
4. Dip a second Pyrex test tube filled with vegetable oil into the bowl of oil. Remove any air bubbles and ask whether the glass is still visible.
5. Explain that Pyrex becomes invisible in oil because both have the same refractive index.
6. As a finale, pull the hidden Pyrex beaker out of the oil for a surprise reveal.
7. Discuss with students using key terms such as refraction, refractive index, and cloaking.

Index of Refraction - disappearing glassware demonstration - Homemade Science with Bruce Yeany:

The Disappearing Test Tube - MWMmaths:

📄 INVISIBLE GLASS EXPERIMENT - Puffing Billy Railway: https://puffingbillyrailway.org.au/wp-content/uploads/SCIENCE-WEEK-GLASS-EXPERIMENT-final.pdf

• Use different clear liquids (e.g., glycerin, corn syrup) to compare visibility of Pyrex.
• Try the demonstration with other transparent materials like acrylic or plastic.
• Use colored light or lasers to make the refraction effects more visible.
• Connect the demonstration to forensic science by showing how refractive index is used to match glass fragments at crime scenes.

• Take care handling oily glassware - it becomes slippery.
• Clean up spills promptly to prevent slipping hazards.
• Dispose of oil safely; do not pour large amounts down the drain.
• Use paper towels for wiping glassware; wash with soap after use.

• Why does Pyrex disappear in vegetable oil but remain visible in water?
• What is refractive index, and how does it relate to the speed of light in different materials?
• Why does light bend when moving from one medium to another?
• How could this principle be applied in real-world uses such as forensics or cloaking technology?
• What would happen if the oil and glass had slightly different refractive indices?