For Convergence 2014 at the beginning of July, my cousin was looking for a replica of the bone blade from the TV show Supernatural. Due to strict regulations, it couldn't be a real weapon. So, I found a different way to make the replica that would fit with the theme of her costume.
The first thing I did was get a piece of 2" pink insulation foam that would fit the length of the blade. I drew a very rough outline of the blade on the foam as a guide. I then began carving the general shape of the blade with a steak knife. The carving starts out incredibly rough, and I only focus on the outer boundaries at first.
I rounded the hilt and moved into the blade, making the 2" foam no wider than 1 1/2" throughout, with the hilt being the widest part of the knife. The details in the teeth and the groove were shaped throughout and provided a guide to creating the right thickness of the blade. The biggest problem was that the foam retained a very polished and finished look with only carving used to create the shape.
I then started to add paint. Instead of focusing just on color application, the spray paint used as a base melted the edges of the foam just enough to decrease the tailored look of the carved foam and add some organic shaping to the blade. Once I was sure I had a good base coat of black and beige, I used some white wall putty to smooth some of the still rough edges, and I let the white show through over the paint base layer. Then I used some acrylic paint and glazes to give it plenty of detail. To finish it up, I sprayed the whole thing with matte fixitive to help hold the color and putty in place.