Chris Oatley has a wonderful blog post about how to create realistic texture in digital painting by examining the techniques of the 19th century Hudson River School of painters. It's really important to open our eyes to history and see how past artists have tackled issues in visual image making and Chris has done a great job analyzing this particular period of realistic artists.
Here's a dump truck that rolled past my studio. Pen and watercolor on Arches hot press, 14" wide. Part of my Trucks watercolor series.