The changing colors seen in soap bubbles or oil floating on water are the result of thin-film interference. These are not the actual colors of the substance itself, but are color changes brought about by its structure. They are a familiar sight to children and, as a subject for study, they can excite scientific curiosity while also being fun to observe. In practical science education, there have been reports of thin-film interference in metal oxide films produced by the anodic oxidation of titanium being used for the development of teaching materials or in teacher training seminars. However, anodic oxidation requires high voltages, and there is also a need to dispose of fluid waste (e.g., phosphoric acid aqueous solution). For this reason, there are few reports of this method being used in practical classes. Within the range of our survey, the interference and diffraction of light has been covered in high school physics classes using soap bubbles, but we found no reports of practical experiments using metal oxide films. Here, we show that after an Sn–Zn binary alloy (85:15 mol%) is heated to melting point, it oxidizes upon exposure to air and interference colors can be observed as a result. The melting point of the Sn–Zn binary alloy is low (198.5 ºC), such that the alloy can be melted using a microwave oven. Furthermore, if the oxide film that forms on the surface of the metal is removed by re-heating, the alloy can be used repeatedly for the experiment. Not only does this cut down the required preparation steps and fluid waste disposal, it also reduces the environmental burden, as the experimental material is reusable. It is theoretically possible to reproduce a given target interference color by adjusting the thickness of the metal oxide film. We compare the temperature characteristics of carbon powder and copper (II) oxide as heating media, in order to determine whether an oxide film can be reliably formed. As a result, we confirm that the oxide film could be formed in a shorter time when using copper (II) oxide as the heating medium.