I had a wooden frame ready for the purpose, which the carpenter had made for me.

Judge of my surprise and delight when I found that the star disc enlarged nearly in the same manner from each side of the focal point, thus making it extremely probable that I had accidentally hit on a near approach to the parabola in the curve of my mirror.

And such proved to be the case.

I have the mirror still, and its performance is very good indeed.
"I went no further with this mirror, for fear or spoiling it.

It is very slightly grey in the centre, but not sufficiently so as to materially injure its performance.