To make each firebox I cut 3 pieces out of the posterboard: 1 for the top, 1 for the bottom, and 1 long piece for the back and sides. To fold the back piece, I first drew the lines where the piece would be folded, then I scored it about 3/4 of the depth of the posterboard with a sharp utility knife. I glued the pieces together with carpenter's glue and a few dots of gel super glue and held the pieces in place with some masking tape.
When dry, I painted it the color of the mortar, then used the magic brick system to create the bricks. I then stippled on black paint using an old fat round brush to look like soot. When all was dry I varnished the firebox with matt varnish.
The earths and most of the surrounds are painted posterboard to look like marble. The one exception is the dining room fireplace. I had a book with pictures of palace furniture. One picture was of a "Pietra Dura" (cut stone) panel from a dresser. I cut up the sections of the picture, glued them onto the posterboard surround with spray adhesive, and then put on 3 coates of glaze. I think it looks great with the painted mantel.
In the kitchen, I wanted a copper hood for the stove. I could only find one size of copper sheet. It was very thick and I had a difficult time cutting and bending it. I had to use metal cutters and made a jig to get accurate folds. I had a piece of molding that had a good shape for the hood, so I glued the copper over it with The Ultimate Glue and finished folding in the sides.
When the piece was dry, I glued on brass strips with The Ultimate glue and gel super glue. I added the brass for 2 reasons: it looked good and it covered up any imperfect cuts or folds. I then cut wood brackets out of full size trim I had left over. It looks like they are supporting the hood and I used them to hold 2 copper cooking utensil bars. When the time came to glue the pieces into place. I first glued in the brackets because the hood was rather heavy and these would help hold it in place. As usual the Ultimate glue and gel super glue worked great. I liked the brackets very much, so I made more to hold a shelf that goes around most of the kitchen.