mike fired this volley in news:kv3o58$bem$1@dont-
email.me:

I tried starting fires with most of them. g The smallest ones that
worked at all were around 6" diameter, and for that I needed a little
ball of red cedar inner bark, like you'd use with flint-and-steel fire
starters.

A 3" mirror with a proper aluminum coating will collect and focus about
4.8 Watts of energy (including losses in reflection) from noon-day sun.

The sun's disk's substended angle of about 0.5 degrees will focus to a
dot of less than 0.1" diameter. That's an area of about 0.008 square
inches. Just to be real generous, let's say 0.01 square inches (for poor
focus).

That's a heat concentration of 480 Watts per square inch. That's not
only enough, but FAR more than enough to ignite any tinder capable of
absorbing the heat.

What'd you try to light, aluminum foil?

Lloyd