Solar Furnace

A solar furnace uses polished lenses to focus light from the sun into a tight beam that can be used to heat materials to temperatures higher than a wood fire. The principle is similar to using a magnifying glass to set a piece of paper on fire, or light a pipe, but larger lenses allow more light to be focused, creating higher temperatures when there is sufficient light hitting the lense from the sun.

An article published in Mother Jones in 1974 by D.S. Halacy,^[1] shared his plans for a "DIY solar project" using a "fresnel lens", which could be used for "soldering, jewelry work (sic.) or firing pottery".

The same Mother Jones article reports that "In France a 35-foot solar furnace has operated for many years, and has performed satisfactorily in melting metals for industrial use. The largest furnace in the United States as of 1974 is that of the Army Quartermaster Corps, which is about the same size."^[2]