Here's another one of my architectural detail sketches, done in Cambridge in the mid-80s. This one's about 5 inches square. I would use tiny scraps of illustration board left over from cutting the pieces for larger artwork. I sketched on site using a Rapidograph pen filled with brown ink. I don't use Rapidograph much any more, since they were so hard to maintain. Faber-Castell's "Pitt" pens are my sketcher of choice. As with the other drawings, I would note the colors with water-soluble colored pencils, then go home and add watercolor to it.
In other news, By-Product readers are now invited to visit the revamped and modernized Pyracantha main website at http://www.pyracantha.com. There is art to see, and the companion art blog to this one, "Quality Art Product." There is also a music section. Other sections are still in development. Profuse thanks to my Webmistress for her patience and skill.