Since I can't post in the how to section for some reason, I thought I'd post here and let
Alan sort it out ?
I stumbled across a picture that illustrates exactly how I photograph my guitars usually now days. It shows just how simple this technique is. I hang my black velvet from a book case and have much less window light - hence long exposures are required (Maybe 1.5secs - but the tripod ensures sharpness).
As you see. No fancy lights required. Just a bit of care. And setting your exposure so the black comes out black - because when a camera sees all that black it assumes it's not meant to be, and wants it to be grey.
Results look like this:
If you spend a lot of time with multiple lights and flashes you can overcome some flaws in this process - like back lighting black headstocks so that there's a bit of rimlight and they don't blend into the blackness - but at an astronomical increase in complexity. Since the sun is millions of miles away, the light does not drop off as it passes across a room. An artificial light will - since the distance to the source is so small. Balancing becomes tricky. Controlling for multiple shadows become tricky. Avoiding multiple hotspots becomes tricky. I.e., a world of pain for the inexperienced.
For this you need: a black velvet cloth. A window. A tripod or method for holding the camera still. A camera that allows you to adjust the exposure (either manual modes or "exposure compensation" (often represented on cameras or phones by a +- icon).