Chimney sweeping brushes are an oft-needed theatre prop required for plays, particularly those set in 19th century London. Chimney brushes are not a common commodity and, thus, are rarely available for purchase; but their simple shape makes them easy for a props builder to fabricate from scratch.
Form several artificial tree branches into a disk-shaped brush top. Some artificial trees already come in pieces of this shape, but if the pieces are smaller and attached to wire, arrange them in a circle with the wire sides in, then twist together the wires at the centre using vice grips. If you need extra wire length, untwist a coat hanger and use it to wrap the pieces together. Wrap tightly to make the finished piece as secure as you can. Make sure that the edges of the disk are even; if they aren't, trim them with tin snips.
Attach the brush top to the top of the curtain rod. Place the tip of the rod in the centre circle of the disk of brushes (it's OK if the centre hole isn't big enough to insert the rod) and secure it in place with duct tape. Wrap the tape up the length of the end of the rod, over the centre of the brush disk, then down the other side of the rod. Do this many times until the brush is fastened securely enough that you can shake it about without the brushes flopping around or falling off.
Spray paint the rod and the brush. Apply black spray paint to the entire apparatus. Pay careful attention to make sure that you fully cover the green tree branches with paint. Let it dry according to the instructions on the can of paint.
Add some soot. Coat the finished chimney sweep brush with ground up paper ash to give it a grainy texture. Spray with fixative if you don't want the soot falling away from the brush during scenes, but leave it loose if you'd like to create the visual effect of the brush spreading soot to everything in its vicinity.