I too am saddened to hear of Fire's passing. I enjoyed reading his daily insights and seeing the marbles he posted for identification. His personality jumped out of every post. RIP.
Spent a little time looking at those marbles—impressive. You're right mine's a similar pattern and size but it's so earth tone and monochrome. I wonder if he made any like this.
My guess is the test pictures are shot with flash. The linked setup uses a light on either side with the flash turned off. The light from the sides helps expose the photo more evenly and keeps it from getting washed out in the center.