One of my favourite mediums is pen & ink.
For several days, I have immersed my art table in found objects as part of the creative process to develop an amulet design for the cover of a fantasy novel.
I use found objects as references for form and colour, and the way light caresses the surface. Handling the real object means I can portray it more convincingly in my illustration.
For the accompanying knife sketch, I borrowed a leather-handled US Army knife to see how the leather wraps the handle, observe reflected light on different surfaces and to feel the weight of the blade.
A little realism is essential for viewers to suspend disbelief. Known realities assist the eye and brain to interpret 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.