For several days, I have immersed my art table in found objects as part of the creative process to develop an amulet design for a fantasy novel.
I use found objects as references for form and colour, observing the way light and shadow caress the surface. Handling the real object enhances my ability to portray it more convincingly in illustration.
For an accompanying knife sketch, I borrowed a leather-handled US Army knife to see how the leather wraps the handle, observed the light reflecting on its surfaces and hefted its weight.
A little realism is essential for viewers to suspend disbelief. Known realities assist the eye and brain to portray a two-dimensional drawing as a completely plausible three-dimensional object. The skill is to retain creativity in the process and to allow the medium to add its own expressive depth to an illustration.