What temperature can be reached with a three-inch magnifying glass in direct sunlight?
1. Indium melts when directly focused on it. Indium has a melting point of 156.6 degrees Celsius. At least this temperature can be reached by focusing the light onto a shiny piece of metal.
To get a higher temperature, I needed to use a dark surface. I charred the surface of a piece of wood with the magnifying glass and placed my metal sample on the dark surface. Upon focusing the light, the metal melted.
2. Tin, bismuth, and lead easily melted. Their respective melting points are 232, 271.5, and 327.5 degrees Celsius. All of these temperature are easily reached by using this method.
3. Zinc melts with difficulty, requiring an extended period of time to warm. Zinc has a melting point of 419.4 degrees Celsius.
4. Magnesium burns with difficulty. This will not work with a large piece of magnesium; to get the magnesium to burn I cut a thin strip of the foil and focused the light on the super-thin and fragile end. Magnesium autoignites at 473 degrees Celsius. Hotter temperatures may be reachable but not very easily by such a primitive method.
5. Titanium does not burn using a dark charred wood base. The wood turns white due to ash formation and disappears from under the titanium, never allowing it to reach the maximum temperature. Titanium autoignites at 1200 degrees Celsius. A different method will need to be tried to determine if this temperature can be attainable.