Where you place the card to reflect in the blade depends on the postion of the knife and the position of the camera. I typically shoot a blade at a slight angle to the camera so whatever is reflected in it will be just off to the side of the camera. I can stand a reflector card just out of the shot on the side or sometimes actually hold it over the blade just above camera range. I often use more than one card because I might be dealing with several different reflecting angles.
One thing to note. A mirror polished blade can sometimes look a little flat or even like a satin finsih with a white card reflected in it. Sometimes you want a little more reflection to show that the blade is shiny. Here is a shot where I held a white piece of cloth above the blade and the wrinkles in the cloth help show how polished the blade is.
In contrast, in the shot below I used a white card and even thought the blade was mirror polished, it really does not show how shiny it is.
Very, very interesting.
Thanks again for your tips and for sharing your obviously
extensive knowledge of knife photography!