Metals produce almost nothing but unpolarised direct reflection this can make them easy to photograph. It is also largely uncontaminated by other indirect reflections. So by learning metal we are learning to photograph direct reflection.
Use a test light /torch at the point where your camera will be. Aim the test light at the point on the metal surface which is nearest to the camera. Use also a test surface(white Card) any point where the light bounces off the test surface gives you the near limit of the family of angles. Mark these spots with tape. If in this position you illuminate all the metal then leave the light there if you do not then aim the light at the furthest point of the metal and mark this family of angles at its extremities on the test card. If the metal object is shapes you can mark several points. You will not need to do this every time however you will remember this for future projects.
NB the point reflecting the metal at the bottom of the image corresponds to the mark at the top of the test surface and vice versa this will help you to find any source of glare on any subject from now on.
So now we have the family of angles the next decision is if we want the metal to appear bright or dark in the picture. This is a critical decision as it leads to two exactly opposing light setups.
If we keep the metal black (high Key scene)
Metal bright almost white (low Key) while keeping the rest of the scene dark.
Firstly in order to have the metal bright we need a light source that fills the family of angles that produce direct reflection. Note that because polished metal produces no diffuse reflection light coming from any other angle will have no effect on the metal regardless of how bright or how long the exposure.
It is important to realise that the light which just fills the family of angles is the minimum light we can use. (later discover why to use a light larger than the minimum) Set up a light on a boom through a diffusion sheet so that the beam fills approximately the family of angles marked earlier. Or use the beam off a reflector card that fills the family of angles. third option to cover with black cards the light from the soft box which we do not require. With the metal on a piece of paper and exposed correctly as per light reading plus open 2 to three stops. You will note the background it black.
How to keep metal dark in the scene. The family of angles we determined earlier allow us to show the metal bright. we must now place our light outside of this family of angles for direct light. By doing so we are placing the light in a way that it can only show diffuse reflection and so as metal reflects almost no diffuse reflection it is almost black. The paper can produce diffuse reflection from a light from any direction and so it is rendered white.
I have tried to do the above experiment again it is difficult. In the end I have opted for a rather large light which fills all the angles necessary for direct light. I had started with a small light however it limited too much my family of angles and made it difficult to get close enough. I also started with a fork which had a rather founded dimension and this also proved difficult.
I then chose a flat piece of metal however it was not so shiny but I managed to get some results. I have first succeeded better by holding up the piece of metal at 90 degrees to the light source ie outside of the family of angles against my white wall I have a black piece of metal against a white background. I have then put the metal in front of the light at a 40 degree angle facing down and the camera by the light and the result is a white piece of metal and my wall seems grey. I have used a large light and my positions were extremes. I will need to practice in different situations to fine tune how to use this normally.
Other Interesting Books The Photographers mind
Science Experiments from Light Science and Magic.
Direct and Diffuse Light on a shiny subject
Using Diffuse Light to show shadow
Working towards assignment 4 Light