Concept sketching is a divergent thinking process. This means you let your mind run free and you come up with many and varied ideas. This requires very quick sketches to capture the basic ideas. The drawings will be small and loosely sketched. The best media for this is pencil or marker pens but any will do. The principle is to not get caught by developing and over-working one idea but to rather just plot down as many as you can. Development follows later.
Pencil and pen capture the basics here. Notice how easily basic lines capture the mood of each figure.
Here the concept is to see how armour would look once worn. Concept sketching allows for all kinds of quick experiments.
Again pencil combining with pen allows us to see this concept for a proper sketch to follow.
Pen and marker pens for this skull idea.
A concept for a ring design inspired by a feather done in pen and marker pens.
Ring concepts leading to a final concept done in pen. Now proper design development should follow.
In the jewellery design profession, designing for a client requires concept drawings to be slightly "neater"/ more developed. This is to assist them to understand and interpret the drawings more accurately. These are all done in pen.
Concept designs for a comic book character.