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<p>[QUOTE=&quot;-jeffB, post: 2001386, member: 27832&quot;]I&#039;ve got a Fresnel lens that&#039;s about 16x20 inches. It will melt silver and zinc. It <i>might</i> soften copper at noon on a cloudless day, but I&#039;ve never succeeded. It won&#039;t do much more than discolor a clad coin.</p><p><br /></p><p>A bigger lens will gather more light/head, but it&#039;ll also focus it into a larger spot -- the size of the spot is proportional to the lens&#039; focal <i>length</i>, but that focal length is usually proportional to the lens&#039; width. My lens focuses to a point larger than the blob on that dime.</p><p><br /></p><p>I suspect a small torch. Radio Shack used to sell a torch that used one cylinder of butane and one cylinder of nitrous oxide, and claimed temperatures up to 5000 degrees F. That thing would melt <i>anything</i>, as long as it was small enough not to carry away the heat too quickly.[/QUOTE]</p><p><br /></p>

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