All you need is a simple chemical reaction to make a genuine silver holiday ornament. An oxidation-reduction (redox) deposits silver on the inside of a glass ball, essentially making a mirror inside the glass. This is a classic holiday chemistry project.
Silver Ornament Materials
These are the materials for one holiday ornament. Simply multiply the quantities to make more ornaments. The materials are readily available online as classroom kits.
- 5 ml acetone or isopropyl alcohol (optional)
- 2.5 ml 0.5 M silver nitrate solution (AgNO3)
- 2.5 ml 1.5 M ammonium nitrate solution (NH4NO3)
- 5 ml 5% dextrose solution (C6H12O6)
- 5 ml 10% sodium hydroxide solution (NaOH)
- distilled water
- clear glass ornament (2-5.8 inches diameter)
- Pipette or dropper, graduated cylinder, small beaker or test tube
- Gently remove the metal ornament hanger from the glass and set it aside. This leaves a hollow glass ball with a short neck.
- Optional: Clean the inside of the glass ball. To do this, use a dropper or pipette to pour a little (about 2 ml) acetone or isopropyl alcohol into the ball. Swirl it around and then dispose of the liquid in a water container. Let the ornament dry before proceeding. The acetone removes residue from the inside of the ornament so you get a more mirror-like silver finish.
- Measure 2.5 ml of silver nitrate solution using a graduated cylinder. Pour the solution into a small beaker or test tube. Rinse the graduated cylinder with water and discard the rinse water.
- Measure 2.5 ml of ammonium nitrate solution using a graduated cylinder. Add the ammonium nitrate solution to the container of silver nitrate solution. Rinse the graduated cylinder with water and discard the liquid.
- Swirl the beaker or test tube to mix the two solutions.
- Measure 5 ml of dextrose solution using the graduated cylinder. Pour the dextrose solution into the dry glass ornament. Rinse the graduated cylinder with water and discard the rinse.
- Measure 5 ml of sodium hydroxide solution using the graduated cylinder.
- Pour the silver nitrate and ammonium nitrate mixture into the glass ball, followed immediately by the sodium hydroxide solution. Cover the glass ball opening with a piece of parafilm and swirl the liquid in the glass ball to completely cover the interior surface. You’ll see the silver mirror coating form as your swirl the liquid.
- When the inside of the ball has an even coating, remove the parafilm and pour the liquid into a waste container.
- Important: Rinse the inside of the glass ball with distilled water and discard the liquid. If you don’t rinse the ornament, a shock-sensitive compound could form.
- Use a dropper or pipette to put about 2 ml of acetone or isopropyl alcohol inside the ornament. Swirl around the acetone and then discard it.
- Let the ornament completely dry. Once it is dry, reattach the hanger and enjoy the decoration. The silver inside this ornament will eventually darken as it oxidizes. To prevent this, you can coat the inside of the ornament with a thin layer of nail polish, varnish, or paint. It doesn’t have to be clear, since the mirror coating is opaque.
- Immediately after the project is complete, add a large volume of water to the waste liquid. The instructor can neutralize the waste by adding 1M HCl until it precipitates silver chloride (AgCl). If desired, the instructor may recover the silver chloride by filtration. The waste solution can be washed down the drain with lots of water.
How Silver Ornaments Work
The silver mirror coating results from a reaction called “Tollens’ test.” Tollens’ test is a qualitative analysis test that distinguishes between an aldehyde and a ketone. An aldehyde, such as dextrose, produces a mirror coating. A ketone does not form a mirror. Mixing the silver nitrate and ammonium nitrate solutions makes a reagent called Tollen’s reagent, which must be prepared fresh for use. The reagent contains the ion [Ag(NH3)2]+. The ion is a weak oxidizing agent, but it’s strong enough to oxidize the aldehyde (-CHO) group on dextrose for form a carboxylate ion (-COO–). The oxidation changes the Ag+ ion into neutral silver metal, which deposits onto the glass.
The overall chemical reaction is:
CH2OH(CHOH)4CHO + 2[Ag(NH3)2]+ + 3OH– → 2Ag(s) + CH2OH(CHOH)4COO– + 4NH3 + 2H2O
CH2OH(CHOH)4CHO is dextrose
[Ag(NH3)2]+ is the silver diammine ion
Read the safety information accompanying the chemicals. Avoid contact with the chemical solutions, as they irritate skin. Be sure to rinse the silvered ornament with water following the chemical reaction. Use care when removing and re-attaching the ornament hanger, as the tops of glass ornaments may be sharp. It’s best to neutralize the residual liquid with acid before disposal, but it’s essential to use copious amounts of water to rinse away the waste. Because this chemistry project uses chemicals and potentially sharp objects, it’s not suitable for very young children. It’s appropriate for middle school, high school, and college chemistry students.
A Related Project
If you have leftover silver nitrate solution, use it to grow a silver crystal holiday tree.
- Curtis, Heber D. (February 1911). “Methods of Silvering Mirrors”. Publications of the Astronomical Society of the Pacific. 23 (135): 15–19. doi:10.1086/122040
- Hart, M. (1992). Manual of scientific glassblowing. St. Helens, Merseyside [England]: British Society of Scientific Glassblowers. ISBN 0-9518216-0-1.
- Svehla, G.; Vogel, Arthur Anton (1996). Vogel’s Qualitative Inorganic Analysis. New York: Longman. ISBN 0-582-21866-7.
- Tollens, B. (1882). “Ueber ammon-alkalische Silberlösung als Reagens auf Aldehyd” [On an ammonical alkaline silver solution as a reagent for aldehydes]. Berichte der Deutschen Chemischen Gesellschaft (in German). 15 (2): 1635–1639. doi:10.1002/cber.18820150243