Place an aluminum sheet on the work surface. Cut out two 7.5 square inch sheets with metal shears.
Mark two trapezoids on an aluminum sheet with these dimensions: 7.5 inches for the base, 9 inches for the top, and 7.5 inches for the height. Cut out the trapezoids with metal shears.
Sand the rough edges of the aluminum pieces with 600-grit sandpaper.
Spray paint the aluminum pieces with black high-temperature grill paint. Allow the paint to dry fully according to the manufacturer's instructions.
Screw one side of a self-closing cabinet hinge into a side of a theater lighting gel frame using a power drill and driver bit with 2 #6-32 3/8-inch screws. Repeat this process on all four sides of the gel frame.
Screw the opposite side of one hinge into the center of the edge of one of the 7.5-inch square pieces using a power drill and driver bit with #6-32 3/8-inch screws. Repeat this process with the remaining 7.5-inch square piece on the opposite side of the gel frame.
Hold the middle of the 7.5-inch edge of one of the trapezoidal pieces over one of the free hinges and screw it in place with a power drill and driver bit using 2 #6-32 3/8-inch screws. Repeat this process with the remaining trapezoidal piece on the remaining free hinge.
Spray paint any unpainted areas of the barn doors and allow the paint to dry fully according to the manufacturer's instructions.
Swing each hinge through its full range of movement to check that they are flexible.