This piece has been effective in shielding the mantle from the stove pipe below it. Previously, the mantle was fairly warm to the touch above the pipe, when the stove was running hot. You could keep your hand on the hotter underside comfortably at all times, however. With the shield, the mantle underside is just barely warm, a very noticeable difference.
The shield is made from 14 in wide aluminum flashing from Home Depot. It's bent in an "L" shape to protect the underside and front. It's secured with 1-5/8 in drywall screws and home made spacers 1 in long, carefully cut and filed from scrap 1/4 in dia soft copper tubing. Flat washers under the screw heads prevent them from deforming the thin sheet metal. Spacing is 1 in at all points. This could have been bent a little more neatly, but it turned out 'OK' for hand work. The sharp edge of a length of 5/4 board was used to create the bend, with the piece clamped to the board. This sort of flashing cuts easily with tin snips or even stout scissors.