Knives present a perennial challenge for theatre propsmasters. As common as dramatic stabbings are in classic plays, staging this violent event in a manner that's both safe and realistic-looking requires a good prop knife. A rubber blade will safely fold against the skin when thrust, and though you can purchase rubber knives, making your own will allow you to create a knife of any shape and size.
Draft the knife shape onto tagboard. Draw freehand, trace a real knife or trace around an image. When finished, you should have a life-size, recognisable knife shape of the style knife you want. Cut out the shape with scissors.
Trace the handle portion of the knife shape only onto wood in pencil.
Cut out the knife handle shape using a scroll saw.
Fit an oscillating power tool with a grinding tip. Use this to grind down the edges of the wooden cutout so that they're rounded, as they are on a real knife. Smooth out the surface of the wood in general and continue grinding the corners until the handle is comfortable to hold. Do not round the top edges where the blade attaches; leave this portion flat.
Remove the knife blade portion from the tagboard cutout. Apply glue generously to the bottom edge of the blade and attach it to the wooden handle. Hold in place until the glue starts to set up. Set aside and let the glue dry fully.
Make a mixture of three parts liquid latex, one part grey acrylic paint; this will create a pale grey colour that will dry to a darker shade. Place the mixture in a tall cup at least as deep as the tagboard blade and deep enough to dip it.
Tie the twine securely to the wooden knife handle. Hang it from a prop or piece of furniture so that the knife blade is pointing downward.
Dip the knife blade into the latex to coat it. Place some scrap paper or a dish beneath the blade to catch drips of latex as it dries. Cover the container with the rest of the latex mixture with kitchen cling film while the latex on the blade dries (about three hours).
Repeat the dipping process to add another layer to the knife. Let dry again and continue to repeat until you've got a blade thick enough to look realistic and stand up on its own.
Untie the knife and wrap the wooden handle with masking tape.
Spray paint the knife handle with silver spray paint. Give each side two coats. Let dry. Remove the masking tape.